Adherence to clinic recommendations among patients with phenylketonuria in the United States

Effects of oral sepiapterin on blood Phe concentration in a broad range of patients with phenylketonuria (APHENITY): results of an international, phase 3, randomised, double-blind, placebo-controlled trial

BACKGROUND

Phenylketonuria is an inherited condition characterised by neurotoxic accumulation of phenylalanine (Phe). APHENITY assessed the efficacy and safety of orally administered synthetic sepiapterin in children and adults with phenylketonuria.

METHODS

APHENITY was a phase 3, randomised, double-blind, placebo-controlled study performed at 34 clinics, hospitals, and university sites in 13 countries. Individuals of all ages with a clinical diagnosis of phenylketonuria were eligible for inclusion if they had a blood Phe concentration of 360 μmol/L or higher at study entry, whereas individuals with hyperphenylalaninaemia due to pathogenic variants in GCH1, PTS, QDPR, SPR, and PCBD1, consistent with a diagnosis of primary BH4 deficiency, were excluded. Part 1 was a 14-day open-label assessment of blood Phe concentration response to sepiapterin. In part 2, sepiapterin-responsive participants were randomly assigned (1:1) by a web-response system based on a block randomisation schedule (permuted block size of 2 and 4) to 6 weeks of sepiapterin (forced-dose escalation: 20, 40, and 60 mg/kg per day per consecutive 2-week period) or placebo. The investigational drug and placebo were identical in their appearance and delivery. Dried blood samples were collected for analysis of Phe concentration on days -1, 1 (before dose was administered), 5, 10, 14, 19, 24, 28, 33, 38, and 42 in part 2, either in-clinic or at home. The primary endpoint for part 2, mean change from baseline in blood Phe after 6 weeks, was assessed in the primary analysis set of participants with at least a 30% reduction in blood Phe concentration in part 1, who took at least one dose in part 2. Safety was evaluated in all participants receiving at least one dose of treatment. The completed study is registered at EudraCT (2021-000474-29) and ClinicalTrials.gov (NCT05099640).

FINDINGS

APHENITY was conducted between Sept 30, 2021, and April 3, 2023. 187 people were assessed for eligibility, of whom 157 were enrolled. In part 1, 156 participants were assessed or evaluated, of whom 114 (73%) were sepiapterin-responsive (ie, ≥15% reduction in blood Phe from baseline). In part 2, 98 participants (49 in the placebo group and 49 in the sepiapterin group) were in the primary analysis set. There was a significant reduction of blood Phe concentration after 6 weeks of sepiapterin (-63%, SD 20) compared with placebo (1%, 29; least squares mean change -395·9 μmol/L, SE 33·8; p<0·0001). Treatment-emergent adverse events were reported in 33 (59%) of 56 participants who received sepiapterin and 18 (33%) of 54 participants who received placebo. Most treatment-emergent adverse events were mild gastrointestinal events (11 [20%] of 56 participants who received sepiapterin and ten [19%] of 54 participants who received placebo) that resolved quickly. There were no deaths and no serious or severe adverse events.

INTERPRETATION

Sepiapterin is a promising oral therapy for individuals with phenylketonuria, was well tolerated, and resulted in significant and clinically meaningful reductions in blood Phe concentration in participants with varying disease severity.

FUNDING

PTC Therapeutics.

Liver gene transfer for metabolite detoxification in inherited metabolic diseases

Inherited metabolic disorders (IMDs) are a growing group of genetic diseases caused by defects in enzymes that mediate cellular metabolism, often resulting in the accumulation of toxic substrates. The liver is a highly metabolically active organ that hosts several thousands of chemical reactions. As such, it is an organ frequently affected in IMDs. In this article, we review current approaches for liver-directed gene-based therapy aimed at metabolite detoxification in a variety of IMDs. Moreover, we discuss current unresolved challenges in gene-based therapies for IMDs.

Factors Affecting Adherence to a Low Phenylalanine Diet in Patients with Phenylketonuria: A Systematic Review

Phenylketonuria (PKU) is an inherited metabolic disorder that requires lifelong adherence to a low-phenylalanine (Phe) diet to prevent severe neurological complications. However, maintaining dietary adherence can be challenging for patients and their families. This systematic review aimed to comprehensively evaluate the factors affecting adherence to a low-Phe diet in patients with PKU. A systematic search of multiple databases was conducted, and 49 studies were included in the final analysis. The quality of evidence was assessed using the Joanna Briggs Institute levels of evidence and the Quality Assessment with Diverse Studies tool. The review identified four main categories of factors influencing dietary adherence: family-related factors (social, psychological, behavioral, and educational), patient-specific factors (psychological, behavioral, educational, and demographic), environmental factors (healthcare professional support, educational and camp-based interventions, and the COVID-19 pandemic), and therapy-related factors (protein substitute formulation, clinic visits, blood tests, and telemedicine). The findings highlight the complex interplay between elements contributing to dietary adherence in PKU patients and underscore the importance of a multifaceted approach to support patients and their families. Future research should prioritize high-quality longitudinal and experimental studies to provide stronger evidence for the PKU community.

Meta-analysis of bone mineral density in adults with phenylketonuria

BACKGROUND

Lifelong management of phenylketonuria (PKU) centers on medical nutrition therapy, including dietary phenylalanine (Phe) restriction in addition to Phe-free or low-Phe medical foods/protein substitutes. Studies have reported low bone mineral density (BMD) in mixed-age PKU populations, possibly related to long-term Phe restriction. Therefore, a meta-analysis investigating BMD specifically in adults with PKU was conducted.

METHODS

Studies reporting BMD-related outcomes were identified from a systematic literature review evaluating somatic comorbidities experienced by adults with PKU on a Phe-restricted diet (searched February 1, 2022, updated November 1, 2023). Risk of study bias was assessed (Scottish Intercollegiate Guidelines Network checklists). The primary outcome of the meta-analysis was pooled mean BMD Z-scores of different bones. Secondary outcomes were the prevalence of low BMD Z-scores at pre-specified thresholds. Subgroup analyses of mean BMD Z-scores (decade of study publication, controlled versus uncontrolled blood Phe levels, gender) were conducted.

RESULTS

BMD-related data from 4097 individuals across 10 studies rated as at least acceptable quality were included. Mean BMD Z-scores were statistically significantly lower compared with an age-matched control or reference (non-PKU) population, across bones, but still within the expected range for age (> -2.0): lumbar spine (seven studies, n = 304), -0.63 (95% confidence interval (CI): -0.74, -0.52); femoral neck (four studies, n = 170), -0.74 (95% CI: -1.25, -0.22); radius (three studies, n = 114), -0.77 (95% CI: -1.21, -0.32); total body (four studies, n = 157), -0.61 (95% CI: -0.77, -0.45). The small number of observations in the subgroup analyses resulted in a high degree of uncertainty, limiting interpretation. Estimated prevalence of BMD Z-scores ≤ -2.0 was 8% (95% CI: 5%, 13%; four studies, n = 221) and < -1.0 was 42% (95% CI: 35%, 51%; five studies, n = 144).

CONCLUSIONS

Adults with PKU had lower BMD Z-scores than the reference (non-PKU) population but < 1 in 10 were below the expected range for age. The low number of studies prevents identification of which population characteristics are most impacting BMD. This meta-analysis was supported by BioMarin Pharmaceutical Inc., Novato, CA and is registered with the Research Registry (reviewregistry1476).

The challenge of adults with phenylketonuria who have been lost to care; a single center's attempt to reach those diagnosed with PKU over 60 years of newborn screening

Background

Those diagnosed with PKU in the early years of newborn screening (NBS) were often discharged from clinic in childhood. Long-term lost to clinic patients may be impacted by untreated PKU and uninformed about current recommendations. We aimed to contact adults away from clinic for 5-50+ years, share current recommendations, offer clinical care, and elicit factors underlying not returning to clinic.

Methods

Former patients were identified and offered a virtual meeting with a physician and dietitian for structured interview and education about current guidelines and treatments.

Results

We identified 53 eligible patients who had PKU and had not returned to clinic in ≥5 years. Of those 53, 27 were successfully contacted, 16 completed the educational intervention, and 5/16 returned to clinic. Reasons for having been away from clinic included discharge from clinic in childhood and inadequate insurance coverage. Experiences varied and some denied negative impacts after diet discontinuation. Individuals expressed a desire for convenient treatments that aligned with overall health goals. Most participants who completed the educational intervention expressed interest in returning to clinic; however, most did not return within the timeframe of the project. All 27 individuals successfully contacted agreed to be re-contacted with future updates or research opportunities.

Discussion

We successfully contacted half of individuals identified as having been lost to clinic follow-up long-term. Limitations included inability to make initial contact, and unwillingness to re-engage by some we reached. Those who agreed to participation desired ongoing PKU clinic and community connection. This experience will inform our process to engage current patients and re-engage those currently lost to care.

Initial results from the PHEFREE longitudinal natural history study: Cross-sectional observations in a cohort of individuals with phenylalanine hydroxylase (PAH) deficiency

Over fifty years have passed since the last large scale longitudinal study of individuals with PAH deficiency in the U.S. Since then, there have been significant changes in terms of treatment recommendations as well as treatment options. The Phenylalanine Families and Researchers Exploring Evidence (PHEFREE) Consortium was recently established to collect a more up-to-date and extensive longitudinal natural history in individuals with phenylketonuria across the lifespan. In the present paper, we describe the structure and methods of the PHEFREE longitudinal study protocol and report cross-sectional data from an initial sample of 73 individuals (5 months to 54 years of age) with PAH deficiency who have enrolled. Looking forward, the study holds the promise for advancing the field on several fronts including the validation of novel neurocognitive tools for assessment in individuals with PKU as well as evaluation of the long-term effects of changes in metabolic control (e.g., effects of Phe-lowering therapies) on outcome.

Executive functions & metabolic control in phenylketonuria (PKU) and mild hyperphenylalaninemia (mHPA)

BACKGROUND

Due to newborn screening and early treatment, patients with phenylketonuria (PKU) and mild hyperphenylalaninemia (mHPA) develop largely normal, in terms of IQ testing and academic attainment. However, the impact of metabolic control in various stages of development on more complex cognitive abilities, i.e. executive functions (EF), is still unclear.

METHODS

EFs were tested in 28 patients with PKU/mHPA, aged 8-17 years, identified by newborn screening and continuously treated. The relation to current (testing day & past 10 phenylalanine (Phe) values) and long-term metabolic control (age periods: childhood <6, 6-10, adolescence >10 years, lifetime Phe) was analyzed.

RESULTS

EFs were in the lower normative range (IQR of T-values: 47.35-51.00). Patients reaction time was significantly slower than the population mean (divided attention/TAP: median 40, p < 0.01). Both, long-term and current metabolic control correlated with performance in EF tests: Higher current Phe impaired reaction times (Go/No-Go, r = -0.387; working memory, r = -0.425; p < 0.05) and performance in planning ability (ToL r = -0.465, p < 0.01). Higher long-term Phe values both in childhood and adolescence mainly affected attention (omissions/TAP r = -0.357 and - 0.490, respectively, both p < 0.05) as well as planning ability (ToL r = -0.422 and - 0.387, adolescence and lifetime, p < 0.05).

CONCLUSION

Current and long-term metabolic control in PKU/mHPA, including the adolescent period, influence EFs, especially affecting reaction time and planning abilities. This should be taken into account in patient counselling.

Patient and carer perceptions of video, telephone and in-person clinics for Phenylketonuria (PKU)

BACKGROUND

In phenylketonuria (PKU), attending multidisciplinary clinic reviews is an important aspect of life-long care. Since the COVID-19 pandemic, video and telephone clinics are used as alternative methods for people with PKU to have contact with their care team. There is limited research concerning patient preference, experience and perceptions of alternative types of clinic review. Individuals from the UK with PKU and their caregivers were invited to complete an online questionnaire, hosted on the National Society for PKU (NSPKU) website and social media platform.

RESULTS

Data was available from 203 respondents. Forty one per cent of respondents (n = 49/119) preferred in-person clinics; 41% (n = 49) a hybrid of in-person, video and telephone clinics; 9% (n = 11) video clinics only, 6% (n = 7) telephone only and 3% (n = 3) were unsure. The main respondent obstacles to in-person clinics were costs, travel and time, but this was balanced by the benefits of a physical examination and better patient engagement/motivation. Twenty one per cent (n = 36/169) of respondents were uncomfortable with the number of healthcare professionals (HCPs) in a clinic room. Patients were less likely to consult with a doctor on video (64%, n = 91/143) or phone (50%, n = 59/119) reviews compared to in-person (80%, n = 146/183). Issues with video and telephone reviews included the shorter time length of review, distractions, technical issues and poor patient engagement.

CONCLUSIONS

Online video and telephone clinic platforms were effective in overcoming the challenging circumstances in management, monitoring and treatment of patients with PKU during the COVID-19 pandemic. However, in-person clinics remain the preferred respondent option. It is important that HCPs are flexible, enabling people with PKU a choice of clinic options according to their individual clinical need and circumstances.

Nutrient Status and Intakes of Adults with Phenylketonuria

A phenylalanine-restricted diet, supplemented with protein substitutes (PSs), remains the cornerstone of phenylketonuria (PKU) management. However, adherence is challenging in adulthood, and data on the nutritional status of early and continuously treated adults with PKU (ETAwPKU) are scarce. A total of 34 ETAwPKU (16 females; mean ± SD, age: 28 ± 9 years, phenylalanine concentration: 847 ± 285 µmol/L) and 34 age- and sex-matched control subjects were compared regarding their blood nutrient status, self-reported dietary intake, and cognitive wellbeing. Though diet adherence varied, all ETAwPKU were taking a PS. No significant differences were found for blood DHA, calcium, ferritin, transferrin, and zinc concentrations. However, selenium and ubiquinone concentrations were 16% and 29% lower in ETAwPKU, respectively (p < 0.01 and <0.0001). Vitamin concentrations (D, B12, B6, and folic acid) were significantly higher in ETAwPKU except for alpha-tocopherol. Amino acid (AA) concentrations differed between ETAwPKU and controls: they were significantly lower for 12 AAs and higher for phenylalanine and glycine. ETAwPKU had a significantly higher intake of most minerals and vitamins, except for niacin and phosphorus (no difference). Depending on the nutrient, PSs represented 52-100% of patients' daily intake and 19% of total daily energy intake. Compared with controls, ETAwPKU scored significantly lower in three of the four subscales of the cognitive wellbeing questionnaire. Overall, the blood DHA and micronutrient status of ETAwPKU was adequate, except for selenium, with higher intakes than controls for most micronutrients. Patients relied heavily on PSs to meet the recommended intakes for protein, DHA, and micronutrients. The potential clinical impact of differences found in AA status should be further studied.

Systematic literature review of the somatic comorbidities experienced by adults with phenylketonuria

BACKGROUND

Phenylketonuria (PKU) is an inborn error of phenylalanine (Phe) metabolism that, if untreated, causes Phe accumulation in the brain leading to neurophysiologic alterations and poor outcomes. Lifelong management centers on dietary Phe restriction, yet long-term complete metabolic control is unachievable for many adults. High blood Phe levels or chronic Phe and intact protein restriction in the diet may lead to somatic comorbidities. A systematic literature review was conducted to evaluate somatic comorbidities experienced by adults with PKU.

METHODS

Clinical and observational studies reporting somatic comorbidities experienced by individuals with PKU aged ≥ 16 years (or classified as adults) evaluating a Phe-restricted diet with or without pharmacologic therapy versus no therapeutic intervention (including healthy controls), or pharmacologic therapy versus a Phe-restricted diet alone, were identified. PubMed® was searched (February 1, 2022 and updated November 1, 2023), using a pre-defined search strategy, followed by two-stage screening and data extraction. Included studies were grouped by PKU population comparison.

RESULTS

1185 records were screened; 51 studies across 12,602 individuals were extracted. Bone-related abnormalities were the most reported outcome (n = 21); several outcome measures were used. Original study groupings included: Phe-restricted diet versus healthy controls or reference values (n = 40); treatment-adherent versus those non-adherent (n = 12). Additional groups added as part of a protocol amendment included: different Phe-restricted diets (n = 4); severe versus less severe disease (n = 5). Vote counting indicated a higher burden of ≥ 1 comorbidity (or outcome measure) for the Phe-restricted diet group by 37 of 38 studies included in the analysis of Phe-restricted diet versus healthy controls; higher burden in healthy controls was reported in 12 studies. Vote counting was similar between those treatment adherent (n = 7) versus non-adherent (n = 10).

CONCLUSIONS

Adults with PKU have a higher comorbidity burden than a non-PKU population. More robust studies are needed to better understand the relationship between effective metabolic control and comorbidity burden, using consistent outcome measures. This SLR was supported by BioMarin Pharmaceutical Inc., Novato, CA, and is registered with the Research Registry (reviewregistry1476).

Navigating social determinants of health barriers in the management of phenylketonuria

Phenylketonuria (PKU) is an inborn error of amino acid metabolism that is typically identified by newborn screening. With lifelong treatment consisting of dietary management, frequent laboratory monitoring, and regular metabolic clinic visits, patients with PKU can maintain good health and metabolic control. Here, we describe the case of an 8-year-old patient with PKU who has been followed by a metabolic clinic since birth. Despite responsiveness to sapropterin, this patient has had periods of poor metabolic control throughout her life due to her family's economic hardships, including limited access to transportation, housing, food, and health insurance. This case illustrates how social determinants of health may negatively affect rare disease management and potential strategies for addressing barriers to care.

Evaluating Therapy and Growth in Children with Phenylketonuria: A Retrospective Longitudinal Study from Two Romanian Centers

Background and Objectives: Phenylketonuria (PKU) is a rare genetic disorder characterized by the inability to convert the essential amino acid phenylalanine into tyrosine. Early dietary treatment can successfully prevent complications, but controversies still exist regarding the attainment of normal growth in these patients. Materials and Methods: Eighteen patients with PKU from two Romanian reference centers were compared to eighteen non-PKU controls, matched for age and gender. The comparisons used weight-for-height, weight-for-age, height/length-for-age, and body mass index-for-age z-scores from birth to three years of age. Results: The PKU study group consisted of nine boys and nine girls, with a median follow-up period of thirty-six months (interquartile range = 9.75). While median values of all four growth metrics remained within the normal range across the entire study period, weight-for-age z-scores were significantly lower in PKU patients throughout most of the study (p < 0.001). Conclusions: The persistent lower weight-for-age z-scores of the PKU patients compared to controls indicate that ongoing monitoring and potential adjustments in dietary therapy may be necessary to further optimize growth outcomes.

Blood Phenylalanine Levels in Patients with Phenylketonuria from Europe between 2012 and 2018: Is It a Changing Landscape?

BACKGROUND

In 2011, a European phenylketonuria (PKU) survey reported that the blood phenylalanine (Phe) levels were well controlled in early life but deteriorated with age. Other studies have shown similar results across the globe. Different target blood Phe levels have been used throughout the years, and, in 2017, the European PKU guidelines defined new targets for blood Phe levels. This study aimed to evaluate blood Phe control in patients with PKU across Europe.

METHODS

nine centres managing PKU in Europe and Turkey participated. Data were collected retrospectively from medical and dietetic records between 2012 and 2018 on blood Phe levels, PKU severity, and medications.

RESULTS

A total of 1323 patients (age range:1-57, 51% male) participated. Patient numbers ranged from 59 to 320 in each centre. The most common phenotype was classical PKU (n = 625, 48%), followed by mild PKU (n = 357, 27%) and hyperphenylalaninemia (HPA) (n = 325, 25%). The mean percentage of blood Phe levels within the target range ranged from 65 ± 54% to 88 ± 49% for all centres. The percentage of Phe levels within the target range declined with increasing age (<2 years: 89%; 2-5 years: 84%; 6-12 years: 73%; 13-18 years: 85%; 19-30 years: 64%; 31-40 years: 59%; and ≥41 years: 40%). The mean blood Phe levels were significantly lower and the percentage within the target range was significantly higher (p < 0.001) in patients with HPA (290 ± 325 μmol/L; 96 ± 24%) and mild PKU (365 ± 224 μmol/L; 77 ± 36%) compared to classical PKU (458 ± 350 μmol/L, 54 ± 46%). There was no difference between males and females in the mean blood Phe levels (p = 0.939), but the percentage of Phe levels within the target range was higher in females among school-age children (6-12 years; 83% in females vs. 78% in males; p = 0.005), adolescents (13-18 years; 62% in females vs. 59% in males; p = 0.034) and adults (31-40 years; 65% in females vs. 41% in males; p < 0.001 and >41 years; 43% in females vs. 28% in males; p < 0.001). Patients treated with sapropterin (n = 222) had statistically significantly lower Phe levels compared to diet-only-treated patients (mean 391 ± 334 μmol/L; percentage within target 84 ± 39% vs. 406 ± 334 μmol/L; 73 ± 41%; p < 0.001), although a blood Phe mean difference of 15 µmol/L may not be clinically relevant. An increased frequency of blood Phe monitoring was associated with better metabolic control (p < 0.05). The mean blood Phe (% Phe levels within target) from blood Phe samples collected weekly was 271 ± 204 μmol/L, (81 ± 33%); for once every 2 weeks, it was 376 ± 262 μmol/L, (78 ± 42%); for once every 4 weeks, it was 426 ± 282 μmol/L, (71 ± 50%); and less than monthly samples, it was 534 ± 468 μmol/L, (70 ± 58%).

CONCLUSIONS

Overall, blood Phe control deteriorated with age. A higher frequency of blood sampling was associated with better blood Phe control with less variability. The severity of PKU and the available treatments and resources may impact the blood Phe control achieved by each treatment centre.

Pegvaliase for the treatment of phenylketonuria: Final results of a long-term phase 3 clinical trial program

Phenylketonuria (PKU) is a genetic disorder caused by deficiency of the enzyme phenylalanine hydroxylase (PAH), which results in phenylalanine (Phe) accumulation in the blood and brain, and requires lifelong treatment to keep blood Phe in a safe range. Pegvaliase is an enzyme-substitution therapy approved for individuals with PKU and uncontrolled blood Phe concentrations (>600 μmol/L) despite prior management. Aggregated results from the PRISM clinical trials demonstrated substantial and sustained reductions in blood Phe with a manageable safety profile, but also noted individual variation in time to and dose needed for a first response. This analysis reports longer-term aggregate findings and characterizes individual participant responses to pegvaliase using final data from the randomized trials PRISM-1 (NCT01819727) and PRISM-2 (NCT01889862), and the open-label extension study 165-304 (NCT03694353). In 261 adult participants with a mean of 36.6 months of pegvaliase treatment, 71.3%, 65.1%, and 59.4% achieved clinically significant blood Phe levels of ≤600, ≤360, and ≤ 120 μmol/L, respectively. Some participants achieved blood Phe reductions with <20 mg/day pegvaliase, although most required higher doses. Based on Kaplan-Meier analysis, median (minimum, maximum) time to first achievement of a blood Phe threshold of ≤600, ≤360, or ≤ 120 μmol/L was 4.4 (0.0, 54.0), 8.0 (0.0, 57.0), and 11.6 (0.0, 66.0) months, respectively. Once achieved, blood Phe levels remained below clinical threshold in most participants. Sustained Phe response (SPR), a new method described within for measuring durability of blood Phe response, was achieved by 85.5%, 84.7%, and 78.1% of blood Phe responders at blood Phe thresholds of ≤600, ≤360, or ≤ 120 μmol/L, respectively. Longer-term safety data were consistent with previous reports, with the most common adverse events (AEs) being arthralgia, injection site reactions, headache, and injection site erythema. The incidence of most AEs, including hypersensitivity AEs, was higher during the early treatment phase (≤6 months) than later during treatment. In conclusion, using data from three key pegvaliase clinical trials, participants treated with pegvaliase were able to reach clinically significant blood Phe reductions to clinical thresholds of ≤600, ≤360, or ≤ 120 μmol/L during early treatment, with safety profiles improving from early to sustained treatment. This study also supports the use of participant-level data and new ways of looking at durable blood Phe responses to better characterize patients' individual PKU treatment journeys.

Poor adherence during adolescence is a risk factor for becoming lost-to-follow-up in patients with phenylketonuria

Purpose

A high rate of lost to follow-up (LTFU) in patients with phenylketonuria (PKU) represents a main challenge. In this study, we investigated potential risk factors for becoming LTFU related to adolescence as a critical period of life.

Methods

We retrospectively analyzed longitudinal data collected from 1993 to 2019 of patients diagnosed with classic PKU that were followed at our center during adolescence (14-18 y) and at least once in adulthood (>18 y). Patients who interrupted their contact with our center after the 18th birthday for at least 2 years were classified as LTFU. We performed a multivariate regression analysis to investigate following potential risk factors for becoming LTFU in adult life: sex, dietary compliance during adolescence assessed through the mean of the annual medians of phenylalanine plasma values, average number of contacts with the center during adolescence and age at first visit after the 18th birthday.

Results

93 patients (52 males, 41 females) were included in the study. 58% became LTFU during adulthood. The mean age at the last visit before becoming LTFU was 26.2 ± 5.1 years. In the multivariate Cox regression analysis we found that poor dietary compliance during adolescence was significantly associated with a higher risk of becoming LTFU during adulthood (p-value = 0.028).

Discussion

Adult patients who displayed poor treatment adherence during adolescence should be identified and carefully monitored to prevent loss of contact.

Vitamin Status in Patients with Phenylketonuria: A Systematic Review and Meta-Analysis

The published data on the vitamin status of patients with phenylketonuria (PKU) is contradictory; therefore, this systematic review and meta-analysis evaluated the vitamin status of PKU patients. A comprehensive search of multiple databases (PubMed, Web of Sciences, Cochrane, and Scopus) was finished in March 2024. The included studies compared vitamin levels between individuals diagnosed with early-treated PKU and healthy controls while excluding pregnant and lactating women, untreated PKU or hyperphenylalaninemia cases, control groups receiving vitamin supplementation, PKU patients receiving tetrahydrobiopterin or pegvaliase, and conference abstracts. The risk of bias in the included studies was assessed by the Newcastle-Ottawa scale. The effect sizes were expressed as standardised mean differences. The calculation of effect sizes with 95% CI using fixed-effects models and random-effects models was performed. A p-value < 0.05 was considered statistically significant. The study protocol was registered in the PROSPERO database (CRD42024519589). Out of the initially identified 11,086 articles, 24 met the criteria. The total number of participants comprised 770 individuals with PKU and 2387 healthy controls. The meta-analyses of cross-sectional and case-control studies were conducted for vitamin B12, D, A, E, B6 and folate levels. PKU patients demonstrated significantly higher folate levels (random-effects model, SMD: 1.378, 95% CI: 0.436, 2.320, p = 0.004) and 1,25-dihydroxyvitamin D concentrations (random-effects model, SMD: 2.059, 95% CI: 0.250, 3.868, p = 0.026) compared to the controls. There were no significant differences in vitamin A, E, B6, B12 or 25-dihydroxyvitamin D levels. The main limitations of the evidence include a limited number of studies and their heterogeneity and variability in patients' compliance. Our findings suggest that individuals with PKU under nutritional guidance can achieve a vitamin status comparable to that of healthy subjects. Our study provides valuable insights into the nutritional status of PKU patients, but further research is required to confirm these findings and explore additional factors influencing vitamin status in PKU.

Satisfaction with home blood sampling methods and expectations for future point-of-care testing in phenylketonuria: Perspectives from patients and professionals

INTRODUCTION

Phenylketonuria (PKU) requires regular phenylalanine monitoring to ensure optimal outcome. However, home sampling methods used for monitoring suffer high pre-analytical variability, inter-laboratory variability and turn-around-times, highlighting the need for alternative methods of home sampling or monitoring.

METHODS

A survey was distributed through email and social media to (parents of) PKU patients and professionals working in inherited metabolic diseases in Denmark, The Netherlands, and United Kingdom regarding satisfaction with current home sampling methods and expectations for future point-of-care testing (POCT).

RESULTS

210 parents, 156 patients and 95 professionals completed the survey. Countries, and parents and patients were analysed together, in absence of significant group differences for most questions. Important results are: 1) Many patients take less home samples than advised. 2) The majority of (parents of) PKU patients are (somewhat) dissatisfied with their home sampling method, especially with turn-around-times (3-5 days). 3) 37% of professionals are dissatisfied with their home sampling method and 45% with the turn-around-times. 4) All responders are positive towards developments for POCT: 97% (n = 332) of (parents of) patients is willing to use a POC-device and 76% (n = 61) of professionals would recommend their patients to use a POC-device. 5) Concerns from all participants for future POC-devices are costs/reimbursements and accuracy, and to professionals specifically, accessibility to results, over-testing, patient anxiety, and patients adjusting their diet without consultation.

CONCLUSION

The PKU community is (somewhat) dissatisfied with current home sampling methods, highlighting the need for alternatives of Phe monitoring. POCT might be such an alternative and the community is eager for its arrival.

Relative Oral Bioavailability and Food Effects of Two Sepiapterin Formulations in Healthy Participants

Sepiapterin is an orally administered drug in development for the treatment of phenylketonuria, an inborn error of metabolism characterized by the deficiency of the phenylalanine-metabolizing enzyme phenylalanine hydroxylase. This study characterized the pharmacokinetics, safety, and tolerability of 2 clinical sepiapterin formulations (Phase 1/2, Phase 3) and the effects of food on the pharmacokinetics of the Phase 3 formulation in healthy participants. In Part A, 18 participants were randomized to one of 2 treatment sequences, each with 4 dosing periods comprising a single dose (20 or 60 mg/kg) of the Phase 1/2 or the Phase 3 formulation with a low-fat diet. In Part B, 14 participants were randomized to one of 2 sequences, each comprising 4 dosing periods of a single dose (20 or 60 mg/kg) of the Phase 3 formulation under fed (high-fat) or fasted conditions. Following oral administration, sepiapterin was quickly absorbed and rapidly and extensively converted to tetrahydrobiopterin (BH4). BH4 was the major circulating active moiety. Under low-fat conditions, the Phase 3 formulation was bioequivalent to the Phase 1/2 formulation at 20 mg/kg, while slightly lower BH4 exposure (approximately 0.81×) for the Phase 3 formulation was observed at 60 mg/kg. BH4 exposure increased to approximately 1.7× under the low-fat condition and approximately 2.8× under the high-fat condition at a dose of either 20 or 60 mg/kg for the Phase 3 formulation, compared with the fasted condition. Both sepiapterin formulations were well tolerated, with no serious or severe adverse events reported. All treatment-emergent adverse events were mild or moderate in severity.

Evaluating change in diet with pegvaliase treatment in adults with phenylketonuria: Analysis of phase 3 clinical trial data

Phenylketonuria (PKU), a genetic disorder characterized by phenylalanine hydroxylase (PAH) deficiency and phenylalanine (Phe) accumulation, is primarily managed with a protein-restricted diet and PKU-specific medical foods. Pegvaliase is an enzyme substitution therapy approved for individuals with PKU and uncontrolled blood Phe concentrations (>600 μmol/L) despite prior management. This analysis assessed the effect of pegvaliase on dietary intake using data from the Phase 3 PRISM-1 (NCT01819727), PRISM-2 (NCT01889862), and 165-304 (NCT03694353) clinical trials. Participants (N = 250) had a baseline diet assessment, blood Phe ≥600 μmol/L, and had discontinued sapropterin; they were not required to follow a Phe-restricted diet. Outcomes were analyzed by baseline dietary group, categorized as >75%, some (>0% but ≤75%), or no protein intake from medical food. At baseline, mean age was 29.1 years, 49.2% were female, mean body mass index was 28.4 kg/m2, and mean blood Phe was 1237.0 μmol/L. Total protein intake was stable up to 48 months for all 3 baseline dietary groups. Over this time, intact protein intake increased in all groups, and medical protein intake decreased in those who consumed any medical protein at baseline. Of participants consuming some or >75% medical protein at baseline, 49.1% and 34.1% were consuming no medical protein at last assessment, respectively. Following a first hypophenylalaninemia (HypoPhe; 2 consecutive blood Phe measurements <30 μmol/L) event, consumption of medical protein decreased and consumption of intact protein increased. Substantial and sustained Phe reductions were achieved in all 3 baseline dietary groups. The probability of achieving sustained Phe response (SPR) at ≤600 μmol/L was significantly greater for participants consuming medical protein versus no medical protein in an unadjusted analysis, but no statistically significant difference between groups was observed for probability of achieving SPR ≤360 or SPR ≤120 μmol/L. Participants with alopecia (n = 49) had longer pegvaliase treatment durations, reached HypoPhe sooner, and spent longer in HypoPhe than those who did not have alopecia. Most (87.8%) had an identifiable blood Phe drop before their first alopecia episode, and 51.0% (n = 21/41) of first alopecia episodes with known duration resolved before the end of the HypoPhe episode. In conclusion, pegvaliase treatment allowed adults with PKU to lower their blood Phe, reduce their reliance on medical protein, and increase their intact and total protein intake. Results also suggest that HypoPhe does not increase the risk of protein malnutrition in adults with PKU receiving pegvaliase.

Supplementation for Performance and Health in Patients with Phenylketonuria: An Exercise-Based Approach to Improving Dietary Adherence

Supplementation is crucial for improving performance and health in phenylketonuria (PKU) patients, who face dietary challenges. Proteins are vital for athletes, supporting muscle growth, minimizing catabolism, and aiding muscle repair and glycogen replenishment post-exercise. However, PKU individuals must limit phenylalanine (Phe) intake, requiring supplementation with Phe-free amino acids or glycomacropeptides. Tailored to meet nutritional needs, these substitutes lack Phe but fulfill protein requirements. Due to limited supplement availability, athletes with PKU may need higher protein intake. Various factors affect tolerated Phe levels, including supplement quantity and age. Adhering to supplement regimens optimizes performance and addresses PKU challenges. Strategically-timed protein substitutes can safely enhance muscle synthesis and sports performance. Individualized intake is essential for optimal outcomes, recognizing proteins' multifaceted role. Here, we explore protein substitute supplementation in PKU patients within the context of physical activity, considering limited evidence.

The investigation of serum phenylalanine levels based on infant feeding method: a cross-sectional study of children less than two years old with phenylketonuria (PKU)

BACKGROUND

Clinical advice may suggest discontinuing breastfeeding after the diagnosis of phenylketonuria in infants as the only effective way to monitor the newborn's intake and accurate measurement of phenylalanine (Phe). This study aims to investigate the prevalence and duration of breastfeeding, as well as its effect on serum Phe levels in infants with phenylketonuria at Education and Therapy Medical Center, Be'sat Hospital, Iran.

METHODS

We conducted a cross-sectional study of 34 children under two years old diagnosed with phenylketonuria between September 2018 and December 2022. Infants were categorized as breastfed and non-breastfed (bottle-fed) based on their feeding method after diagnosis. Data on age at diagnosis, medical records, demographic information, and anthropometric indices were collected, and infants with incomplete data or mixed feeding (formula + breast milk) were excluded from the study.

RESULTS

Of 94 infants managed in our hospital, 34 had complete medical records. Among the all patients 13 (38%) continued to be breastfed combined with phenylalanine-free amino acid-based protein substitute, while 21 (62%) were did not receive breast milk. The mean duration of breastfeeding was 2.57 ± 0.59 (1-3) months. The mean age at diagnosis was 22.6 ± 18.4 days. Phenylalanine concentrations at diagnosis were mean 10, SD 5.44; range 4-24 mg/dL [0.22-1.33 μmol/L] in the breastfed group and mean 14.3, SD 10.2; range 5-37 mg/dL [0.27-2.05 μmol/L] in the non-breastfed group.Non-breastfed infants had lower serum Phe levels than breastfed infants: mean 3.76, SD 2.10; range 1-7 mg/dL [0.05-0.38 μmol/L] and mean 4.89, SD 3.68; range 2-19 mg/dL [0.11-1.05 μmol/L], respectively, although not statistically significant [(t (34) = 118.0, P = 0.51]. Also we found no significant associations in body measurements for weight, height, and head circumference at birth and final assessment.

CONCLUSIONS

In conclusion, during treatment, there were no statistically significant associations between breastfeeding and serum Phe levels with growth in children with phenylketonuria.

Odimet®: A Pioneering Tele-Health Tool to Empower Dietary Treatment and the Acute Management of Inborn Errors of Metabolism-An Assessment of Its Effectiveness during the COVID Pandemic

Strict adherence to a diet is an essential pillar of long-term treatment for many inborn errors of metabolism (IEMs). Tools that educate patients about dietary management can positively condition adherence and prevent morbidity. We designed a free online dietary calculation program (Odimet®, version 2.1.) for IEMs patients in 2008, updated in 2022, that provides detailed information on the content of amino acids, protein, lipids, carbohydrates, vitamins and minerals in >3000 food products, including specific medical foods for IEM. We analyzed the statistics on visits to Odimet® to evaluate its usefulness for long-term dietary management during a 5-year period focusing on three periods: pre-pandemic (15 March 2018-14 March 2020); pandemic 1 (15 March 2020-14 March 2021); and pandemic 2 period (15 March 2021-15 March 2023), in 120 patients with the following distribution: 84 patients with phenylketonuria (PKU); 12 with maple syrup urine disease (MSUD); 11 with urea cycle disorders (UCDs); and 13 with classical galactosemia. The evolutionary levels of their specific metabolic markers were evaluated, showing that globally, both pediatric and adult patients maintain a good metabolic control, even during a pandemic (median levels of phenylalanine in pediatric PKU patients 213.4 µmol/L and 482.3 µmol/L in adults; of leucine in MSUD patients: 144.2 µmol/L; of glutamine in UCDs: 726.8 µmol/L; and of galactose 1-phosphate levels in galactosemia: 0.08 µmol/L). The proportion of patients using Odimet® ranges from 78-100%. An increase in the number of diets being calculated was observed during COVID-19 pandemic. Currently, 14,825 products have been introduced (3094 from the general database, and 11,731 added by users to their own profiles). In 2023 63 emergency dietary adjustments in the studied intoxication-type pathologies were calculated in Odimet®. Our results suggest that its regular use contributes to maintaining metabolic stability in IEMs patients, allowing them to adapt their menus to their lifestyle, and represents a powerful complementary tele-health tool which can be used to perform remote real-time dietary follow-up.

A base editing strategy using mRNA-LNPs for in vivo correction of the most frequent phenylketonuria variant

The c.1222C>T (p.Arg408Trp) phenylalanine hydroxylase (PAH) variant is the most frequent cause of phenylketonuria (PKU), an autosomal recessive disorder characterized by accumulation of blood phenylalanine (Phe) to neurotoxic levels. Here we devised a therapeutic base editing strategy to correct the variant, using prime-edited hepatocyte cell lines engineered with the c.1222C>T variant to screen a variety of adenine base editors and guide RNAs in vitro, followed by assessment in c.1222C>T humanized mice in vivo. We found that upon delivery of a selected adenine base editor mRNA/guide RNA combination into mice via lipid nanoparticles (LNPs), there was sufficient PAH editing in the liver to fully normalize blood Phe levels within 48 h. This work establishes the viability of a base editing strategy to correct the most common pathogenic variant found in individuals with the most common inborn error of metabolism, albeit with potential limitations compared with other genome editing approaches.

Best practice recommendations for the management of anxiety during the pegvaliase journey

BACKGROUND

Pegvaliase, an enzyme substitution therapy, is a treatment option for phenylketonuria (PKU). Due to the neuropathophysiology and disease burden of PKU, individuals can experience baseline anxiety unrelated to pegvaliase therapy. In addition, there are aspects of pegvaliase therapy that may be anxiety-inducing for those considering or receiving treatment. The aim of this manuscript is to present best practice recommendations for the identification and management of anxiety symptoms that can occur along the pegvaliase journey.

METHODS

A modified Delphi approach was used to seek consensus among a multidisciplinary panel of experts. To this end, an in-person meeting was held that was preceded by a medical specialist- and patient-specific survey to develop preliminary recommendations on ways to address anxiety along the pegvaliase journey. After the meeting, an additional survey was conducted to rank the proposed solutions and mitigation strategies from which a set of recommendations was developed. All recommendations were voted on with the aim of consensus generation, defined as achieving ≥75% agreement among experts.

RESULTS

The panel reached consensus on a total of 28 best practice recommendations for the management of anxiety during the pre-treatment, induction and titration, early maintenance (pre-efficacy), and late maintenance (post-efficacy) stages. The recommendations offer strategies to identify and address the most common causes of pegvaliase-related anxiety, including self-injection, side effects, the titration schedule, prescribed dietary changes, and variable time to efficacy. Overall, managing anxiety in those considering or receiving pegvaliase involves patient-centered communication, shared decision-making, and personalized treatment plans.

CONCLUSIONS

The best practice recommendations described herein can guide healthcare providers in proactively addressing anxiety during the different stages of pegvaliase treatment, and support providers with initiating and managing pegvaliase in individuals who may experience baseline and treatment-related anxiety.

Long-term comparative effectiveness of pegvaliase versus medical nutrition therapy with and without sapropterin in adults with phenylketonuria

Phenylketonuria is characterized by intellectual disability and behavioral, psychiatric, and movement disorders resulting from phenylalanine (Phe) accumulation. Standard-of-care treatment involves a Phe-restricted diet plus medical nutrition therapy (MNT), with or without sapropterin dihydrochloride, to reduce blood Phe levels. Pegvaliase is an injectable enzyme substitution treatment approved for adult patients with blood Phe >600 μmol/L despite ongoing management. A previous comparative effectiveness analysis using data from the Phase 3 PRISM trials of pegvaliase (NCT01819727 and NCT01889862) and the Phenylketonuria Demographics, Outcomes and Safety Registry (PKUDOS; NCT00778206) suggested that pegvaliase was more effective at lowering mean blood Phe levels than sapropterin + MNT or MNT alone at 1 and 2 years of treatment. The current work augments and complements the previous analysis by including additional follow-up from the completed studies, robust methods reflecting careful consideration of issues with the distribution of Phe, and alternative methods for adjustment that are important for control of potential confounding in comparative effectiveness. Median blood Phe levels were lower, and median intact protein intakes were higher, in the pegvaliase group (n = 183) than in the sapropterin + MNT (n = 82) and MNT (n = 67) groups at Years 1, 2, and 3. In the pegvaliase group, median blood Phe levels decreased from baseline (1244 μmol/L) to Year 1 (535 μmol/L), Year 2 (142 μmol/L), and Year 3 (167 μmol/L). In the sapropterin + MNT group, median blood Phe levels decreased from baseline (900 μmol/L) to Year 1 (588 μmol/L) and Year 2 (592 μmol/L), and increased at Year 3 (660 μmol/L). In the MNT group, median blood Phe levels decreased slightly from baseline (984 μmol/L) to Year 1 (939 μmol/L) and Year 2 (941 μmol/L), and exceeded baseline levels at Year 3 (1157 μmol/L). The model-estimated proportions of participants achieving blood Phe ≤600 μmol/L were 41%, 100%, and 100% in the pegvaliase group at Years 1, 2, and 3, respectively, compared with 55%, 58%, and 38% in the sapropterin + MNT group and 5%, 16%, and 0% in the MNT group. The estimated proportions of participants achieving more stringent blood Phe targets of ≤360 μmol/L and ≤120 μmol/L were also higher in the pegvaliase group than in the other groups at Years 2 and 3. Overall, our results indicate that, compared with standard therapy, pegvaliase induces a substantial, progressive, and sustained decrease in blood Phe levels - to a much greater extent than sapropterin + MNT or MNT alone - which is expected to improve long-term outcomes in patients with phenylketonuria.

State-of-the-art 2023 on gene therapy for phenylketonuria

Phenylketonuria (PKU) or hyperphenylalaninemia is considered a paradigm for an inherited (metabolic) liver defect and is, based on murine models that replicate all human pathology, an exemplar model for experimental studies on liver gene therapy. Variants in the PAH gene that lead to hyperphenylalaninemia are never fatal (although devastating if untreated), newborn screening has been available for two generations, and dietary treatment has been considered for a long time as therapeutic and satisfactory. However, significant shortcomings of contemporary dietary treatment of PKU remain. A long list of various gene therapeutic experimental approaches using the classical model for human PKU, the homozygous enu2/2 mouse, witnesses the value of this model to develop treatment for a genetic liver defect. The list of experiments for proof of principle includes recombinant viral (AdV, AAV, and LV) and non-viral (naked DNA or LNP-mRNA) vector delivery methods, combined with gene addition, genome, gene or base editing, and gene insertion or replacement. In addition, a list of current and planned clinical trials for PKU gene therapy is included. This review summarizes, compares, and evaluates the various approaches for the sake of scientific understanding and efficacy testing that may eventually pave the way for safe and efficient human application.

Efficient in vivo prime editing corrects the most frequent phenylketonuria variant, associated with high unmet medical need

The c.1222C>T (p.Arg408Trp) variant in the phenylalanine hydroxylase gene (PAH) is the most frequent cause of phenylketonuria (PKU), the most common inborn error of metabolism. This autosomal-recessive disorder is characterized by accumulation of blood phenylalanine (Phe) to neurotoxic levels. Using real-world data, we observed that despite dietary and medical interventions, most PKU individuals harboring at least one c.1222C>T variant experience chronic, severe Phe elevations and do not comply with Phe monitoring guidelines. Motivated by these findings, we generated an edited c.1222C>T hepatocyte cell line and humanized c.1222C>T mouse models, with which we demonstrated efficient in vitro and in vivo correction of the variant with prime editing. Delivery via adeno-associated viral (AAV) vectors reproducibly achieved complete normalization of blood Phe levels in PKU mice, with up to 52% whole-liver corrective PAH editing. These studies validate a strategy involving prime editing as a potential treatment for a large proportion of individuals with PKU.

Pharmacodynamics, safety, tolerability and pharmacokinetics of a single oral dose of an engineered phenylalanine ammonia-lyase in patients with phenylketonuria

The cornerstone treatment of hyperphenylalaninemia (HPA) and phenylketonuria (PKU) is a lifelong low-protein diet with phenylalanine (Phe) free L-amino acid supplements. However, the PKU diet has significant shortcomings, and there is a clinically unmet need for new therapeutics to improve patient outcomes. CDX-6114 is a modified phenylalanine ammonia-lyase (PAL) enzyme obtained by a mutation in the Anabaena variabilis PAL sequence. CodeEvolver® protein engineering technology has been applied to improve the degradation resistance of the enzyme. In our first phase I trial, 19 patients were given a single oral dose of CDX-6114 at 7.5 g, 2.5 g, 0.7 g, or placebo in a cross-over design. After an overnight fast, patients received a standardised breakfast of 20 g of protein, thus exceeding the dietary recommendations for a single meal in patients with PKU. Plasma levels of Phe and cinnamic acid (CA) were measured over a 5-h period following CDX-6114 dosing. During the development of CDX-6114, a stability assessment using reverse-phase high-performance liquid chromatography (HPLC) assay revealed two peaks. The second peak was identified as CA. It was not previously known that as part of the mechanism of action, the CA remained associated with the protein following the conversion of Phe. Thus, recalculating the historical PAL enzyme amounts in CDX-6114 bulk substance was necessary. An updated extinction coefficient was achieved by applying a correction factor of 0.771 to previously reported doses. Postprandial plasma levels of Phe increased in all dose cohorts over time between 10% and 30% from baseline, although the actual peak of Phe levels was not achieved within the 5-h observation. When accounting for the interquartile ranges, these concentrations were similar to the placebo. As plasma levels of Phe were no longer a reliable marker for pharmacodynamics, the consistently detectable amount of CA seen in all patients who received CDX-6114 provided proof of the enzymatic activity of CDX-6114 in metabolising gastrointestinal Phe. Peak levels of CA were seen shortly after CDX-6114 intake, with a rapid decline, and remained low compared with the plasma Phe levels. This pattern indicates a short half-life, possibly due to the liquid formulation or the inability to withstand the lower pH in the human stomach compared with animal models in earlier studies. This was the first trial in patients with PKU to establish the safety and tolerability of CDX-6114. A single dose of CDX-6114 was safe and well tolerated, with no serious adverse events or presence of anti-drug antibodies detected. Efficacy will be explored in future trials using an optimised formulation.

Nutritional status of adults with phenylketonuria on pegvaliase: A 15-month prospective study

Background

Pegvaliase has allowed many adults with phenylketonuria (PKU) to achieve acceptable blood Phe control while eating an unrestricted diet. However, little is known about potential differences in nutritional status and eating behaviors after transitioning from a phenylalanine (Phe)-restricted to an unrestricted diet. Here we assessed change in nutritional status in adults with early-treated PKU who were consuming a Phe-restricted diet (intact protein ≤0.8 g/kg/day) prior to starting pegvaliase.

Methods

A 15-month, prospective, longitudinal study to assess change in anthropometrics, dietary intake, laboratory indices of nutritional status, bone mineral density (BMD), body composition, measured resting energy expenditure (REE), and eating behaviors between baseline and Month 15.

Results

Eleven adults (n = 7 female) aged 19.5-52.9 years completed the study. Six participants had a substantial blood Phe reduction (responders) and five participants had a modest blood Phe reduction (partial responders) by Month 15. Intact protein intake increased by an average of 49.4 g/day and 26.7 g/day in responders and partial responders, respectively. Plasma concentrations of most vitamins, minerals, and essential fatty acids assessed were normal, though micronutrient intakes decreased as participants decreased or discontinued PKU medical food(s). Responders had a more variable change in body mass index (BMI) and lean mass index (LMI) compared to partial responders, though there were no clear trends in BMD or body composition changes. Total protein intake was positively correlated with LMI. Responders, but not partial responders, self-reported increased in enjoyment of food and decreased food neophobia, uncontrolled eating, and emotional eating.

Discussion

Participants transitioning to an unrestricted diet while on pegvaliase maintained adequate nutritional status overall with no clinically significant changes in cardiovascular or glycemic markers. Responders reported improvements in eating behaviors, including reduced food neophobia, uncontrolled eating, and emotional eating, and increased enjoyment of food. There were no consistent trends in BMD, body composition, or BMI changes. A larger sample size and longer follow-up period are needed to further assess potential changes.

Natural Protein Intake in Children with Phenylketonuria: Prescription vs. Actual Intakes

In phenylketonuria (PKU), an important component of the UK dietary management system is a 50 mg phenylalanine (Phe)/1 g protein exchange system used to allocate the Phe/natural protein intakes according to individual patient tolerance. Any foods containing protein ≤ 0.5 g/100 g or fruits/vegetables containing Phe ≤ 75 mg/100 g are allowed without measurement or limit. In children with PKU, we aimed to assess the difference between the prescribed natural protein intake and their actual consumed intake, and to calculate the natural protein/Phe intake from foods given without measurement or restriction. Over a 6-month duration, three one-day diet diaries were collected every month by caregivers of children with PKU at the beginning of a follow-up study. Dietary intakes of Phe, as well as natural and total protein intakes, were calculated using Nutritics® (v5.09). Weekly blood Phe spots were collected by caregivers. The target blood Phe level was ≤360 μmol/L for ages up to 12 years and ≤600 μmol/L for ages ≥12 years. Sixteen early treated children (69% females) with PKU were recruited. The median age was 11 years (range: 9-13), and most had classical PKU (n = 14/16). A median of 18 (range 12-18) one-day diaries and 22 blood spots were analysed for each subject over 6 months. The median prescribed natural protein was 6 g/day (range: 3-27), but when calculated, the actual median intake from all foods consumed was 10 g/day (range: 4-37). The median prescribed Phe was 300 mg/day (range: 150-1350), but the actual median intake was 500 mg/day (range: 200-1850). The median difference between the prescribed and actual natural protein daily intakes was +4 g/day (range: -2.5 to +11.5), with a median percentage increase of 40% for natural protein/Phe intake (p < 0.001). The median blood Phe level was 250 μmol/L (range 20-750), with 91% of blood Phe levels within the target range. Only one patient (11 years) had less than 75% of their blood Phe levels within the target range. The UK Phe exchange system provides flexibility in the dietary management of PKU. With this method, the actual natural protein intake was 167% higher than the prescribed amount. Although this led to a variable daily protein intake, the majority of children (n = 15/16) experienced no deterioration in their metabolic control.

Two-year interim safety and efficacy of pegvaliase in Japanese adults with phenylketonuria

Phenylketonuria (PKU) is an inborn error of metabolism caused by deficiency of phenylalanine hydroxylase, resulting in high blood phenylalanine (Phe) concentrations with potential for impaired neurocognition. Pegvaliase, a pegylated recombinant phenylalanine ammonia lyase that metabolizes Phe, is approved for use in adults with PKU and high blood Phe despite prior management. In the Phase 3 PRISM studies conducted in the United States, pegvaliase induction/titration/maintenance dosing led to clinically meaningful and statistically significant blood Phe reductions versus placebo, with a manageable safety profile. Here we report the primary endpoint, change in blood Phe levels from baseline to Week 52, and 2-year interim efficacy and safety results (to Week 144; data cut-off March 31, 2022) of an ongoing, open-label study in a Japanese PKU population (JapicCTI-194,642). Participants were 12 adults with PKU from Japan aged 18-70 years with blood Phe levels >600 μmol/L. In Part 1, participants received subcutaneous 2.5 mg pegvaliase once weekly for 4 weeks (induction), followed by titration up to 20 mg/day, then dose adjustment to a maximum 40 mg/day to achieve blood Phe efficacy (≤360 μmol/L); this maintenance dose was continued to Week 52. In Part 2, participants continued pegvaliase with dose adjustments up to a maximum 60 mg/day for up to 168 weeks. Among 11 participants evaluable for efficacy, mean (standard deviation) blood Phe concentration decreased from 1025.9 (172.7) μmol/L at baseline to 448.3 (458.8) μmol/L at Week 52 (mean 57.5% decrease). Up to Week 104, all 11 (100%) efficacy-evaluable participants achieved blood Phe levels ≤600 μmol/L, 9 (81.8%) achieved ≤360 μmol/L, and 8 (72.7%) achieved ≤120 μmol/L. All 12 participants reported ≥1 adverse event (AE), most commonly injection site erythema and injection site swelling (n = 10, 83.3% each). The pegvaliase exposure-adjusted AE rate was 23.5 per person-years overall, 41.2 per person-years during induction/titration, and 13.5 per person-years during maintenance. All participants developed pegvaliase-induced antibody responses. There were no AEs leading to discontinuation, no deaths, and no anaphylaxis events. Although interim, these results support the use of pegvaliase in Japanese adults with PKU with elevated blood Phe levels and are consistent with results from the Phase 3 PRISM studies.

Adult PKU Clinics in the UK-Users' Experiences and Perspectives

Adults with PKU require life-long management, and ideally, their care should be in a specialised adult metabolic clinic. Their outcomes and co-morbidities have received much attention, but data are lacking on their experience, satisfaction and expectations about the care they receive. This survey reports the experiences and care adults with PKU receive from specialist metabolic clinics in the UK. The online survey developed by the UK NSPKU (National Society for Phenylketonuria), was placed on the NSPKU website from February 2021 to December 2022, and was completed by adults with PKU (≥18 years) or their carers/family members. Sixty-five adult PKU patients and 9 caregivers of adult patients completed the questionnaire (63% female in total). Only 32% of respondents were following a Phe-restricted diet with protein substitute intake as prescribed; the rest were partially adherent or not on dietary restrictions. Nineteen per cent (n = 14/74) had not been reviewed in clinic for two years. Half of the respondents (50%) described their experience in adult clinics as "good". Half of the patients were unable to contact their dietitians with questions or concerns, and only 24% considered that they received adequate support. Clinic reviews usually included anthropometric (82%) and dietary assessments (64%), discussion on management of PKU in daily life (78%) and a blood test (71%). Eighty-eight per cent reported they had at least one neurocognitive, mental health or behavioural co-morbidity but less than half of the patients reported an assessment on their neurocognitive functioning or mental health issues. Adult male patients appeared to have less detailed clinic review than females. Less than half (44%) of the respondents reported that they performed a blood spot for blood Phe at least monthly, but only 32% considered they had been informed about the risk of high Phe levels in adulthood. Although time, cost and stress related to travelling were barriers to a face-to-face review, more than 40% of patients had concerns about remote appointments. The frequency and extent of monitoring of adults with PKU, attending specialist adult services, were less than those specified by the PKU European guidelines. The care of women of reproductive age is prioritised over men. Adult metabolic health services require further attention, development and resources to provide a high standard and equitable service to patients with PKU.

Expert Consensus on the Long-Term Effectiveness of Medical Nutrition Therapy and Its Impact on the Outcomes of Adults with Phenylketonuria

Many adults with phenylketonuria (PKU) rely on medical nutrition therapy (MNT; low phenylalanine (Phe) diet with protein substitutes/medical foods) to maintain blood Phe concentrations within recommended ranges and prevent PKU-associated comorbidities. Despite disease detection through newborn screening and introduction of MNT as early as birth, adherence to MNT often deteriorates from childhood onwards, complicating the assessment of its effectiveness in the long term. Via a modified Delphi process, consensus (≥70% agreement) was sought on 19 statements among an international, multidisciplinary 13-member expert panel. After three iterative voting rounds, the panel achieved consensus on 17 statements related to the limitations of the long-term effectiveness of MNT (7), the burden of long-term reliance on MNT (4), and its potential long-term detrimental health effects (6). According to the expert panel, the effectiveness of MNT is limited in the long term, is associated with a high treatment burden, and demonstrates that adults with PKU are often unable to achieve metabolic control through dietary management alone, creating an unmet need in the adult PKU population.

Neuropsychiatric Function Improvement in Pediatric Patients with Phenylketonuria

OBJECTIVE

To evaluate effects of sapropterin dihydrochloride on blood phenylalanine (Phe) and symptoms of neuropsychiatric impairment in children and adolescents with phenylketonuria (PKU).

STUDY DESIGN

PKU subjects 8-17 years of age (n = 86) were randomized to double-blind treatment with sapropterin (n = 43) or placebo (n = 43) for 13 weeks, then all received open-label sapropterin therapy for an additional 13 weeks. Blood Phe and symptoms of inattention, hyperactivity/impulsivity (Attention-Deficit/Hyperactivity Disorder Rating Scale IV [ADHD RS-IV]), executive functioning (Behavior Rating Inventory of Executive Function), depression (Hamilton Rating Scale for Depression), and anxiety (Hamilton Rating Scale for Anxiety) were assessed.

RESULTS

Following the 13-week randomization phase, the sapropterin and placebo groups had mean changes in blood Phe of -20.9% and +2.9%, respectively. Corresponding least square mean differences in ADHD RS-IV scores were significantly greater for the sapropterin vs the placebo group: Total (-3.2 points, P = .02), Inattention subscale (-1.8 points, P = .04), and Hyperactivity/Impulsivity subscale (-1.6 points, P = .02). Forest plots favored sapropterin treatment over placebo for all ADHD RS-IV and Behavior Rating Inventory of Executive Function indices. There were no significant differences in reported problems with attention or executive function between the 2 groups at baseline or at week 26 following the 13-week open-label treatment period. Anxiety and depression scores did not differ significantly between cohorts at any time. Sapropterin was well tolerated, with a favorable safety profile.

CONCLUSIONS

Sapropterin reduced blood Phe and was associated with significant improvement in parent-reported symptoms of inattention, hyperactivity/impulsivity, and executive functioning in children and adolescents with PKU.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01114737. Registered 27 April 2010, https://clinicaltrials.gov/ct2/show/NCT01114737.

Evaluation of a New 'Mix-In' Style Glycomacropeptide-Based Protein Substitute for Food and Drinks in Patients with Phenylketonuria and Tyrosinemia

(1) Background: Poor palatability, large volume, and lack of variety of some liquid and powdered protein substitutes (PSs) for patients with phenylketonuria (PKU) and tyrosinemia (TYR) can result in poor adherence. This study aimed to evaluate a new unflavoured, powdered GMP-based PS designed to be mixed into drinks, foods, or with other PSs, in patients with PKU and TYR. (2) Methods: Paediatric and adult community-based patients were recruited from eight metabolic centres and prescribed ≥1 sachet/day (10 g protein equivalent (PE)) of the Mix-In-style PS over 28 days. Adherence, palatability, GI tolerance, and metabolic control were recorded at baseline and follow-up. Patients who completed at least 7 days of intervention were included in the final analysis. (3) Results: Eighteen patients (3-45 years, nine males) with PKU (n = 12) and TYR (n = 6) used the Mix-In-style PS for ≥7 days (mean 26.4 days (SD 4.6), range 11-28 days) alongside their previous PS, with a mean intake of 16.7 g (SD 7.7) PE/day. Adherence was 86% (SD 25), and GI tolerance was stable, with n = 14 experiencing no/no new symptoms and n = 3 showing improved symptoms compared to baseline. Overall palatability was rated satisfactory by 78% of patients, who successfully used the Mix-In-style PS in various foods and drinks, including smoothies, squash, and milk alternatives, as a top-up to meet their protein needs. There was no concern regarding safety/metabolic control during the intervention. (4) Conclusions: The 'Mix-In'-style PS was well adhered to, accepted, and tolerated. Collectively, these data show that providing a flexible, convenient, and novel format of PS can help with adherence and meet patients' protein needs.

Evaluation of a New Glycomacropeptide-Based Protein Substitute in Powdered and Liquid Format in Patients with PKU

(1) Background: Good adherence to a Phe-restricted diet supplemented with an adequate amount of a protein substitute (PS) is important for good clinical outcomes in PKU. Glycomacropeptide (cGMP)-PSs are innovative, palatable alternatives to amino acid-based PSs (AA-PS). This study aimed to evaluate a new cGMP-PS in liquid and powder formats in PKU. (2) Methods: Children and adults with PKU recruited from eight centres were prescribed at least one serving/day of cGMP-PS for 7-28 days. Adherence, acceptability, and gastrointestinal tolerance were recorded at baseline and the end of the intervention. The blood Phe levels reported as part of routine care during the intervention were recorded. (3) Results: In total, 23 patients (powder group, n = 13; liquid group, n = 10) completed the study. The majority assessed the products to be palatable (77% of powder group; 100% of liquid group) and well tolerated; the adherence to the product prescription was good. A total of 14 patients provided blood Phe results during the intervention, which were within the target therapeutic range for most patients (n = 11) at baseline and during the intervention. (4) Conclusions: These new cGMP-PSs were well accepted and tolerated, and their use did not adversely affect blood Phe control.

Total choline intake and working memory performance in adults with phenylketonuria

BACKGROUND

Despite early diagnosis and compliance with phenylalanine (Phe)-restricted diets, many individuals with phenylketonuria (PKU) still exhibit neurological changes and experience deficits in working memory and other executive functions. Suboptimal choline intake may contribute to these impairments, but this relationship has not been previously investigated in PKU. The objective of this study was to determine if choline intake is correlated with working memory performance, and if this relationship is modified by diagnosis and metabolic control.

METHODS

This was a cross-sectional study that included 40 adults with PKU and 40 demographically matched healthy adults. Web-based neurocognitive tests were used to assess working memory performance and 3-day dietary records were collected to evaluate nutrient intake. Recent and historical blood Phe concentrations were collected as measures of metabolic control.

RESULTS

Working memory performance was 0.32 z-scores (95% CI 0.06, 0.58) lower, on average, in participants with PKU compared to participants without PKU, and this difference was not modified by total choline intake (F[1,75] = 0.85, p = 0.36). However, in a subgroup with complete historical blood Phe data, increased total choline intake was related to improved working memory outcomes among participants with well controlled PKU (Phe = 360 µmol/L) after adjusting for intellectual ability and mid-childhood Phe concentrations (average change in working memory per 100 mg change in choline = 0.11; 95% CI 0.02, 0.20; p = 0.02). There also was a trend, albeit nonsignificant (p = 0.10), for this association to be attenuated with increased Phe concentrations.

CONCLUSIONS

Clinical monitoring of choline intake is essential for all individuals with PKU but may have important implications for working memory functioning among patients with good metabolic control. Results from this study should be confirmed in a larger controlled trial in people living with PKU.

Nutrition management of PKU with pegvaliase therapy: update of the web-based PKU nutrition management guideline recommendations

BACKGROUND

The web-based GMDI/SERN PKU Nutrition Management Guideline, published before approval of pegvaliase pharmacotherapy, offers guidance for nutrition management of individuals with phenylketonuria (PKU) treated with dietary therapy and/or sapropterin. An update of this guideline aims to provide recommendations that improve clinical outcomes and promote consistency and best practice in the nutrition management of individuals with PKU receiving pegvaliase therapy. Methodology includes: formulation of a research question; review, critical appraisal, and abstraction of peer-reviewed studies and unpublished practice literature; expert input through Delphi surveys and a Nominal Group process; and external review by metabolic experts.

RESULTS

Recommendations, summary statements, and strength of evidence are included for each of the following topics: (1) initiating a pegvaliase response trial, (2) monitoring therapy response and nutritional status, (3) managing pegvaliase treatment after response to therapy, (4) education and support for optimal nutrition with pegvaliase therapy, and (5) pegvaliase therapy during pregnancy, lactation, and adolescence. Findings, supported by evidence and consensus, provide guidance for nutrition management of individuals receiving pegvaliase therapy for PKU. Recommendations focus on nutrition management by clinicians, as well as the challenges for individuals with PKU as a result of therapy changes.

CONCLUSIONS

Successful pegvaliase therapy allows the possibility for individuals with PKU to consume an unrestricted diet while still maintaining the benefits of blood phenylalanine control. This necessitates a perspective change in education and support provided to individuals in order to achieve healthy nutrient intake that supports optimal nutritional status. The updated guideline, and companion Toolkit for practical implementation of recommendations, is web-based, allowing for utilization by health care providers, researchers, and collaborators who advocate and care for individuals with PKU. These guidelines are meant to be followed always taking into account the provider's clinical judgement and considering the individual's specific circumstances. Open access is available at the Genetic Metabolic Dietitians International ( https://GMDI.org ) and Southeast Regional Genetics Network ( https://managementguidelines.net ) websites.

A method for phenylalanine self-monitoring using phenylalanine ammonia-lyase and a pre-existing portable ammonia detection system

Phenylketonuria is an inborn error of phenylalanine metabolism caused by a phenylalanine hydroxylase deficiency. To prevent the occurrence of neurological symptoms and maternal complications resulting from phenylketonuria, patients must adhere to a strict diet therapy, tetrahydrobiopterin supplementation, or pegvaliase injection to maintain blood phenylalanine levels within a recommended range throughout their lives. Therefore, monitoring blood phenylalanine levels is necessary to determine the recent metabolic status of phenylalanine in patients with PKU; however, there are no available instruments for individuals to monitor their own blood phenylalanine levels using whole fingertip blood. We developed a phenylalanine monitoring system (designated as PheCheck) that included a pre-existing portable ammonia detection device and phenylalanine ammonia-lyase, which converts phenylalanine to trans-cinnamic acid and ammonia. This system was able to remove 86.7% ± 0.03% of the ammonia contained in fingertip blood and successfully reduce background ammonia levels. A good correlation was found between the estimated plasma phenylalanine levels detected by PheCheck and plasma phenylalanine levels detected by high-performance liquid chromatography (R² 0.97). The entire PheCheck process for measuring blood phenylalanine takes only 20 min. PheCheck can lay the foundation for home phenylalanine monitoring with high feasibility because all the components are easily accessible. Further studies with a more user-friendly PheCheck optimized for practice are needed to improve blood phenylalanine control, reduce the burden on patients and/or caregivers, and prevent the sequelae associated with phenylketonuria.

Nutrient Status among Latvian Children with Phenylketonuria

(1) Introduction: Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism. The main treatment for PKU is to manage nutrition, thereby restricting phenylalanine intake. Part of patient management is analyzing eating habits to substitute missing nutrients and limit the overdose of nutrients. This is mainly done by analyzing food diaries. This is the first review of Latvian PKU patients eating habits performed by analyzing 72-h food diaries (FD). (2) Materials and Methods: This study included individuals between the ages of 18 and 31 years, PKU patients and 31 age- and sex-matched control groups. All respondents kept 72-h food diaries (FD) and underwent testing for zinc, selenium and ferritin levels in the blood. Food diary data were analyzed by Nutritics software to calculate the theoretical intake of nutrients, and these values were compared with the Ministry of Health of the Republic of Latvia's recommended values. (3) Results: A lack of motivation and diet therapy compliance in PKU patients was observed during this research. A total of 32% of PKU patients refused to fill out their FD or filled it out incorrectly. The analysis of nutrient intake was observed, and there was a statistically significant difference between PKU patients in the 1-3 age group and the control group in fat intake. Fat intake in PKU patients was below MRHL recommendations. The intake of iron was found to be surplus in all PKU patients in the age group of 1-3, 91% of PKU patients in the age group of 4-6 years, 63% in the age group of 7-12 and 71% in the 13-18 year age group. Although there were no instances in the PKU patients nor the control group who had ferritin levels above the normal range. Selenium intake was surplus in 80% of PKU patients in the 1-3 age group, 91% in PKU patients in the 4-6 age group, 88% in the 7-12 age group and 86% in the 13-18 age group. None of the patients had Se levels in the blood above the normal range. Zn intake was surplus in 100% of PKU patients in the 1-3 age group, 82% in PKU patients in the 4-6 age group, 88% in the 7-12 age group and 57% in the 13-18 age group, and no PKU patients had high Zn levels. None of the control group participants had levels below the normal range of Zn and Se while 11% of PKU patients in the 13-18 age group had inadequate levels of Se, although Se intake based on their FD was optimal. (4) Conclusions: Regular PKU patient nutritional status evaluation is important to define and prevent possible nutrient deficiency, and further investigation should be continued to find out the mechanism of nutrient absorption in PKU patients. To prevent macronutrient deficiency such as fat and micronutrient deficiency in PKU patients, one could use supplements or try an improved nutrient content of Phe-free formula in the future.

Risk of Developing Insulin Resistance in Adult Subjects with Phenylketonuria: Machine Learning Model Reveals an Association with Phenylalanine Concentrations in Dried Blood Spots

Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism where high phenylalanine (Phe) concentrations cause irreversible intellectual disability that can be prevented by newborn screening and early treatment. Evidence suggests that PKU subjects not adherent to treatment could be at risk of insulin resistance (IR). We studied how Phe concentrations (PheCs) relate to IR using machine learning (ML) and derived potential biomarkers. In our cross-sectional study, we analyzed subjects with neonatal diagnoses of PKU, grouped as follows: 10 subjects who adhered to treatment (G1); 14 subjects who suspended treatment (G2); and 24 control subjects (G3). We analyzed plasma biochemical variables, as well as profiles of amino acids and acylcarnitines in dried blood spots (DBSs). Higher PheCs and plasma insulin levels were observed in the G2 group compared to the other groups. Additionally, a positive correlation between the PheCs and homeostatic measurement assessments (HOMA-IRs) was found, as well as a negative correlation between the HOMA-Sensitivity (%) and quantitative insulin sensitivity check index (QUICKI) scores. An ML model was then trained to predict abnormal HOMA-IRs using the panel of metabolites measured from DBSs. Notably, ranking the features' importance placed PheCs as the second most important feature after BMI for predicting abnormal HOMA-IRs. Our results indicate that low adherence to PKU treatment could affect insulin signaling, decrease glucose utilization, and lead to IR.

Characterisation and differential diagnosis of neurological complications in adults with phenylketonuria: literature review and expert opinion

OBJECTIVE

Phenylketonuria (PKU) is a rare inherited metabolic disorder characterised by elevated phenylalanine (Phe) concentrations that can exert neurotoxic effects if untreated or upon treatment discontinuation. This systematic review supported by expert opinion aims to raise awareness among the neurological community on neurological complications experienced by adults with PKU (AwPKU).

METHODS

The PubMed database was searched for articles on neurological signs and symptoms in AwPKU published before March 2022. In addition, two virtual advisory boards were held with a panel of seven neurologists and two metabolic physicians from Germany and Austria. Findings are supported by three illustrative patient cases.

RESULTS

Thirty-nine articles were included. Despite early diagnosis and treatment, neurological signs and symptoms (e.g. ataxia, brisk tendon reflexes, tremor, visual impairment) can emerge in adulthood, especially if treatment has been discontinued after childhood. In PKU, late-onset neurological deficits often co-occur with cognitive impairment and psychiatric symptoms, all of which can be completely or partially reversed through resumption of treatment.

CONCLUSION

Ideally, neurologists should be part of the PKU multidisciplinary team, either to bring lost to follow-up patients back to clinic or to manage symptoms in referred patients, considering that symptoms are often reversible upon regaining metabolic control. The current findings have been combined in a leaflet that will be disseminated among neurologists in Germany and Austria to create awareness.

Two years of pegvaliase in Germany:Experiences and best practice recommendations

BACKGROUND

In 2019, pegvaliase was approved in Europe for the treatment of phenylketonuria (PKU) in patients aged 16 years and older with blood phenylalanine (Phe) concentrations above 600 μmol/L despite prior management with available treatment options. Since its European approval, German metabolic centres have gained valuable experience, which may be of benefit to other treatment centres managing patients on pegvaliase.

METHODS

After a virtual meeting that was attended by nine German physicians, three German dietitians and one American physician, a follow-up discussion was held via an online platform to develop a set of recommendations on the use of pegvaliase in Germany. Eight German physicians contributed to the follow-up discussion and subsequent consensus voting, using a modified Delphi technique. The recommendations were supported by literature and retrospectively collected patient data.

RESULTS

Consensus (≥75% agreement) was achieved on 25 recommendations, covering seven topics deemed relevant by the expert panel when considering pegvaliase an option for the treatment of patients with PKU. In addition to the recommendations, a retrospective chart review was conducted in seven of the centres and included 71 patients who initiated treatment with pegvaliase. Twenty-seven patients had been treated for at least 24 months and 23 (85.2%) had achieved blood Phe ≤600 μmol/L with some degree of diet normalisation. Of these patients, 14 had physiological blood Phe on a normalised diet.

CONCLUSION

The practical consensus recommendations provide guidance on the different steps along the pegvaliase journey from clinical site requirements to treatment goals and outcomes. The recommendations are intended to support less experienced European metabolic centres with the implementation of pegvaliase, emphasising that a core treatment team consisting of at least a dietitian and metabolic physician is sufficient to initiate pegvaliase and support patients during their treatment journey.

Real-world treatment, dosing, and discontinuation patterns among patients treated with pegvaliase for phenylketonuria: Evidence from dispensing data

Background

Phenylketonuria (PKU) is an inborn metabolic error characterized by a deficiency of the enzyme required for the metabolism of phenylalanine, an essential amino acid found in most protein-containing foods. Pegvaliase (Palynziq®) is an enzyme substitution therapy approved for adults with PKU who have inadequate blood phenylalanine control (≥600 μmol/L) on existing management.

Objective

To characterize the treatment, discontinuation, and dosing patterns in patients treated with pegvaliase in real-world practice settings in the United States following commercial availability in 2018.

Study design

Retrospective cohort study using BioMarin's proprietary drug dispense database associated with the pegvaliase REMS program.

Methods

Sample construction identified all patients who properly initiated pegvaliase in real world settings (‘full cohort’) and a subset of patients (‘extended follow-up cohort’) with ≥12 months between first dispense of maximum dose and last pegvaliase dispense. Key outcomes were quantified across patients in both cohorts: maximum daily dose; time to maximum daily dose; maximum daily syringes; and dose escalation over time. The overall dose at discontinuation and time to discontinuation were calculated. Patients who subsequently reinitiated therapy were identified. For the extended follow-up cohort, 12-month changes in dose and syringes and dispensing gaps during the 12 months after maximum dose were quantified across all patients and were further stratified by maximum dose.

Results

Overall, 1596 patients associated with 33,814 dispenses were reflected in the pegvaliase dispense dataset during the study period from July 9, 2018, through December 31, 2021; 1280 patients associated with 25,973 dispenses met inclusion criteria for the full cohort, with 19.9 dispenses each on average. Of these patients, 483 patients associated with 15,149 dispenses also met the extended follow-up criteria, with an average of 31.4 dispenses.

Average treatment duration in the full cohort was 82.2 weeks, including 50.8 weeks after maximum daily dose was achieved. The average maximum daily dose was 30 mg with an average time to maximum dose of 31.8 weeks: 43.0% of patients had a maximum dose of 20 mg, 31.3% a maximum dose of 40 mg, and 12.0% a maximum dose of 60 mg. At data cut-off, 289 patients (22.6%) had discontinued; within this group, 126 patients (43.6%) discontinued within the first 6 months after reaching maximum dose.

The overall average treatment duration for patients in the extended follow up cohort at data cut off was 131.2 weeks, including 98.6 weeks after maximum dose was achieved. The average maximum daily dose across the cohort was 32.9 mg: 42.4% of patients had a maximum dose of 20 mg, 41.0% a maximum dose of 40 mg, and 11.2% a maximum dose of 60 mg. At 12 months after achieving maximum dose, 35% of patients had down-dosed, with a 46.8% decrease (on average) from their maximum dose.

Conclusions

Real-world use of pegvaliase reflects longer titration periods than in the dosing schedule based on trial experience. Over time, a substantial number of patients are able to reduce their daily dose by titrating down from their maximum dose, a finding of great interest to clinicians and patients alike.

Pegvaliase dose escalation to 80 mg daily may lead to efficacy in patients who do not exhibit an optimal response at lower doses

In 2018, pegvaliase was approved as the first enzyme substitution treatment for phenylketonuria (PKU) and is now the second medication available for PKU patients since the approval of sapropterin dihydrochloride in 2007. Historically, dietary management has been the mainstay of treatment for PKU. While sapropterin response rate is limited to approximately 50% of PKU patients, pegvaliase has the potential to reduce phenylalanine levels in all PKU patients (Vockley et al., 2014; Longo et al., 2019 [1,3]). Current FDA labeling for pegvaliase includes a dose maximum of 60 mg daily (Longo et al., 2019; BioMarin Pharmaceutical Inc., 2020 [3,4]). We report a case series of four phenylalanine hydroxylase (PAH) deficient patients, previously treated with dietary management only, who initiated treatment with pegvaliase and were titrated to 80 mg daily dosing. The safety profile in these four cases did not differ from lower maintenance dosing (Longo et al., 2019 [3]). Subsequent decreases in Phe levels were observed on 80 mg maintenance dosing, allowing for individualized dietary liberalization in three out of four patients. We conclude that pegvaliase dosing must be personalized to achieve therapeutic goals and that some patients may require higher doses than those included on the product label.

Management of early treated adolescents and young adults with phenylketonuria: Development of international consensus recommendations using a modified Delphi approach

BACKGROUND

Early treated patients with phenylketonuria (PKU) often become lost to follow-up from adolescence onwards due to the historical focus of PKU care on the pediatric population and lack of programs facilitating the transition to adulthood. As a result, evidence on the management of adolescents and young adults with PKU is limited.

METHODS

Two meetings were held with a multidisciplinary international panel of 25 experts in PKU and comorbidities frequently experienced by patients with PKU. Based on the outcomes of the first meeting, a set of statements were developed. During the second meeting, these statements were voted on for consensus generation (≥70% agreement), using a modified Delphi approach.

RESULTS

A total of 37 consensus recommendations were developed across five areas that were deemed important in the management of adolescents and young adults with PKU: (1) general physical health, (2) mental health and neurocognitive functioning, (3) blood Phe target range, (4) PKU-specific challenges, and (5) transition to adult care. The consensus recommendations reflect the personal opinions and experiences from the participating experts supported with evidence when available. Overall, clinicians managing adolescents and young adults with PKU should be aware of the wide variety of PKU-associated comorbidities, initiating screening at an early age. In addition, management of adolescents/young adults should be a joint effort between the patient, clinical center, and parents/caregivers supporting adolescents with gradually gaining independent control of their disease during the transition to adulthood.

CONCLUSIONS

A multidisciplinary international group of experts used a modified Delphi approach to develop a set of consensus recommendations with the aim of providing guidance and offering tools to clinics to aid with supporting adolescents and young adults with PKU.

The impact on quality of life of diet restrictions and disease symptoms associated with phenylketonuria: a time trade-off and discrete choice experiment study

Phenylketonuria (PKU) is a metabolic disorder leading to a deficiency in the metabolism of phenylalanine (Phe). Elevated Phe levels in the blood, tissue and brain may lead to emotional, cognitive, and physical symptoms in adults. To control blood Phe levels, most individuals with PKU need to follow a strict, life-long Phe-restricted diet. The main objective of this study was to estimate the impact of PKU-related disease symptoms and dietary restrictions on health-related quality of life (HRQoL). This study was designed as a web-based survey using the methods of Time Trade-Off (TTO) and Discrete Choice Experiment with duration (DCE_TTO) in a survey of the Swedish general population and population with PKU. Data were collected using questionnaires for TTO diet (n = 509), TTO symptoms (n = 507), and DCE_TTO (n = 1117). The disutility of diet restrictions ranged from 0.050 for a partially restricted diet without medical food to 0.193 for a fully restricted diet with medical food in the TTO (DCE: 0.043-0.108). The disutility of experiencing symptoms (emotional, cognitive and physical) ranged from 0.148 for mild symptoms to 0.593 for severe symptoms in the TTO (DCE: 0.122-1.522). The study shows that both diet and symptoms have a significant negative impact on HRQoL in PKU and that utility estimates are largely consistent across methods and samples.