Phenylalanine hydroxylase deficiency: diagnosis and management guideline

Assessing the lived experiences of females with phenylketonuria in their health management

Introduction

The present study is a mixed-methods exploratory study aiming to understand the lived experiences of females with phenylketonuria (PKU) in managing their health. The study aims to identify what individual, interpersonal, and environmental factors serve as facilitators and inhibitors, and how PKU intrudes on different realms of health.

Methods

Attendees of Emory's Metabolic Camp and female users of Medical Nutrition Therapy for Prevention (MNT4P) were recruited. Participants were administered the Illness Intrusiveness Ratings Scale (IIRS) survey and qualitatively interviewed. The IIRS survey was analyzed using descriptive statistics and the interviews were coded and assessed using inductive and deductive analysis.

Results

In total, 25 participants were included in analysis (adults, n = 20; adolescents, n = 5). In the IIRS survey, diet had the highest average impact score of 5.74 (SD = 2.05) and religious expression had the lowest average impact score of 1.74 (SD = 1.65). The most salient themes that arose from the qualitative interviews were related to concerns of pregnancy (n = 25), interactions with health care providers relative to PKU care (n = 23) and independent of PKU care (n = 21), social support (n = 21) and isolation (n = 12), financial issues (n = 22), and illness intrusiveness on general health management (n = 22).

Discussion

Adolescent and adult female participants with PKU identified significant concerns in individual, interpersonal, and environmental factors affecting the management of their health. Additionally, the illness intrusiveness of PKU impacted their physical, mental, and gynecological health. Future research should further assess the unique challenges faced by females with PKU and potential interventions to better address these barriers.

Inborn Errors of Metabolism and Pregnancy

As the diagnosis and treatment of patients with inborn errors of metabolism has improved dramatically over the years, more people with these conditions are surviving into child-bearing years. Given the changes in metabolism throughout pregnancy, this time presents a unique challenge in their care. Overall metabolic shifts in pregnancy go from anabolism to catabolism driven by endocrinologic changes, along with changes in rates of gluconeogenesis, glucose consumption, amino acid transport, protein consumption, and lipid breakdown, result in a complicated metabolic picture. Additionally, maternal inborn errors of metabolism can affect a fetus, as in phenylketonuria, and fetal inborn errors of metabolism can affect the mother, as in certain fatty acid oxidation disorders. Data on these conditions is often very limited. A summary of the current literature, risks associated with pregnancy in inborn errors of metabolism, and suggestions for management of these conditions will be presented.

Revealing Metabolic Dysregulation Induced by Polypropylene Nano- and Microplastics in Nile Tilapia via Noninvasive Probing Epidermal Mucus

A noninvasive sampling technology was conceived, employing a disposable acupuncture needle in conjunction with high-resolution mass spectrometry (termed as noninvasive direct sampling extractive electrospray ionization mass spectrometry, NIDS-EESI-MS) to scrutinize the epidermal mucus of Nile tilapia for insights into the metabolic dysregulation induced by polypropylene nano- and microplastics. This analytical method initiates with the dispensing of an extraction solvent onto the needles coated with the mucus sample, almost simultaneously applying a high voltage to generate analyte ions. This innovative strategy obliterates the necessitation for laborious sample preparation, thereby simplifying the sampling process. Employing this technique facilitated the delineation of a plethora of metabolites, encompassing, but not confined to, amino acids, peptides, carbohydrates, ketones, fatty acids, and their derivatives. Follow-up pathway enrichment analysis exposed notable alterations within key metabolic pathways, including the biosynthesis of phenylalanine, tyrosine, and tryptophan, lysine degradation, as well as the biosynthesis and metabolism of valine, leucine, and isoleucine pathways in Nile tilapia, consequent to increased concentrations of polypropylene nanoplastics. These metabolic alterations portend potential implications such as immune suppression, among other deleterious outcomes. This trailblazing application of this methodology not only spares aquatic life from sacrifice but also inaugurates an ethical paradigm for conducting longitudinal studies on the same organisms, facilitating detailed investigations into the long-term effects of environmental pollutants. This technique enhances the ability to observe and understand the subtle yet significant impacts of such contaminants over time.

Restoring function to inactivating G protein-coupled receptor variants in the hypothalamic-pituitary-gonadal axis1

G protein-coupled receptors (GPCRs) are central to the functioning of the hypothalamic-pituitary-gonadal axis (HPG axis) and include the rhodopsin-like GPCR family members, neurokinin 3 receptor, kappa-opioid receptor, kisspeptin 1 receptor, gonadotropin-releasing hormone receptor, and the gonadotropin receptors, luteinizing hormone/choriogonadotropin receptor and follicle-stimulating hormone receptor. Unsurprisingly, inactivating variants of these receptors have been implicated in a spectrum of reproductive phenotypes, including failure to undergo puberty, and infertility. Clinical induction of puberty in patients harbouring such variants is possible, but restoration of fertility is not always a realisable outcome, particularly for those patients suffering from primary hypogonadism. Thus, novel pharmaceuticals and/or a fundamental change in approach to treating these patients are required. The increasing wealth of data describing the effects of coding-region genetic variants on GPCR function has highlighted that the majority appear to be dysfunctional as a result of misfolding of the encoded receptor protein, which, in turn, results in impaired receptor trafficking through the secretory pathway to the cell surface. As such, these intracellularly retained receptors may be amenable to 'rescue' using a pharmacological chaperone (PC)-based approach. PCs are small, cell permeant molecules hypothesised to interact with misfolded intracellularly retained proteins, stabilising their folding and promoting their trafficking through the secretory pathway. In support of the use of this approach as a viable therapeutic option, it has been observed that many rescued variant GPCRs retain at least a degree of functionality when 'rescued' to the cell surface. In this review, we examine the GPCR PC research landscape, focussing on the rescue of inactivating variant GPCRs with important roles in the HPG axis, and describe what is known regarding the mechanisms by which PCs restore trafficking and function. We also discuss some of the merits and obstacles associated with taking this approach forward into a clinical setting.

Emerging biosensors in Phenylketonuria

Phenylketonuria (PKU) is an autosomal recessive metabolic disorder resulting from deficient phenylalanine hydroxylase (PAH) enzyme activity, leading to impaired phenylalanine (Phe) metabolism. This condition can lead to intellectual disability, epilepsy, and behavioural issues. Treatment typically involves strict dietary restrictions on natural protein intake, supplemented with chemically manufactured protein substitutes containing amino acids other than Phe. Various approaches, including casein glycomacropeptide (GMP), tetrahydrobiopterin (BH4), phenylalanine ammonia-lyase (PAL) therapy, large neutral amino acid (LNAA) supplementation, enzyme therapy, gene therapy, and medical therapies, aim to prevent Phe transport in the brain to potentially treat PKU. Although newborn screening programs and early dietary interventions have enhanced outcomes of the potential treatment strategies, limitations still persist in this direction. These involve potent accuracy concerns in diagnosis due to the existence of antibiotics in blood of PKU patients, affecting growth of the bacteria in the bacterial inhibition assay. Monitoring involves complex methods for instance, mass spectrometry and high-pressure liquid chromatography, which involve shortcomings such as lengthy protocols and the need for specialized equipment. To address these limitations, adaptable testing formats like bio/nano sensors are emerging with their cost-effectiveness, biodegradability, and rapid, accurate, and sensitive detection capabilities, offering promising alternatives for PKU diagnosis. This review provides insights into current treatment and diagnostic approaches, emphasizing on the potential applications of the diverse sensors intended for PKU diagnosis.

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.

Management of patients with phenylketonuria (PKU) under enzyme replacement therapy: An Italian model (expert opinion)

Objective

Phenylketonuria (PKU) is a metabolic disorder necessitating lifelong management to prevent severe neurological impairments. This paper synthesises clinical practices from Italian specialist centres to delineate a unified approach for administering pegvaliase, a novel enzyme replacement therapy for PKU.

Methods

Virtual meetings convened in September 2022, gathering a steering committee (SC) of experts from five Italian centres specialising in PKU. The SC reviewed, and discussed clinical practices, and formulated recommendations for pegvaliase treatment.

Results

The SC outlined a comprehensive treatment roadmap for PKU management with pegvaliase, emphasising the importance of multidisciplinary care teams, patient selection, pre-treatment evaluation, and education. Recommendations include initial hospital-based pegvaliase administration, regular monitoring of phenylalanine and tyrosine levels, dietary adjustments, and management of adverse events. A consensus was reached on the need for a digital database to manage treatment plans and enhance communication between healthcare professionals and patients.

Conclusion

The expert panel's consensus highlights the complexity of PKU management and the necessity for a coordinated, patient-centred approach. The recommendations aim to standardise care across Italian centres and provide a framework for integrating pegvaliase therapy into clinical practice, potentially informing international guidelines. Further research is warranted to evaluate the long-term impact of these practices on patient outcomes and quality of life.

Characteristics and outcomes of pregnancies among women with phenylketonuria from the NBS Connect registry

Women with phenylketonuria (PKU) should maintain blood phenylalanine (phe) concentration within the recommended range before and during pregnancy to prevent maternal PKU syndrome (MPKUS) in their offspring. Women who gave birth to children with MPKUS symptoms were more likely to report elevated phe concentration before pregnancy, and barriers to accessing components of their dietary management during pregnancy, including blood phe testing, medical food, modified low-protein foods, and healthcare visits with PKU specialists.

Delays in Newborn Screening for Phenylketonuria from Birth to Diagnosis and Factors Affecting This

This study aims to evaluate the process of neonatal phenylketonuria (PKU) screening from birth to admission to the pediatric metabolism polyclinic, determining delays in the screening program and the factors influencing them. This study was conducted during 2021-2023. Blood collection dates, results, and probable parameters causing delays in the screening program were recorded. This study included 118 infants. Admission time to the polyclinic was (mean ± SD) 25.2 ± 12.6 days (min-max: 3.4-78.9 days). Admission time was significantly high for refugees, those whose parents were consanguineous, and those who had more heel-prick blood samples taken (p < 0.001, p = 0.005, and p < 0.001, respectively). The first heel-prick blood phenylalanine (phe) level was significantly negatively correlated with the admission time (p < 0.001). Patients' admission time whose first blood phe level < 240 μmol/L was statistically significantly higher than in those with ≥240 μmol/L (p < 0.001). We determined that there were delays in PKU screening from birth to admission to the polyclinic. Being a refugee, the presence of consanguineous marriages, the increase in the number of heel-prick tests, and blood phe levels at a range of 120-240 μmol/L were the factors that played a role in this delay. Taking steps to reduce the impact of these parameters can prevent delays in newborn PKU screening and increase the success of the screening program.

Pegvaliase therapy for phenylketonuria: Real-world case series and clinical insights

OBJECTIVE

The aim of this study is to present a series of case studies on the real-life use of pegvaliase in Italy in managing patients affected by phenylketonuria (PKU) and provide practical insight and support to healthcare professionals currently approaching and facing this novel enzyme substitution therapy.

METHODS

A panel of 11 PKU experts from seven leading Italian treatment centers attended online virtual meetings with the aim of reviewing their clinical and practical experiences with pegvaliase based on occurred cases. In selecting the cases, specific consideration was given to the nationwide representation of the centers involved and to the number of patients with PKU managed. Cases were thoroughly reviewed, with comprehensive discussions enabling the identification of key take-home messages regarding pegvaliase therapy.

RESULTS

The panel discussed 18 cases, 11 males and 7 females (age range 17-43 years). At the last follow-up (up to 111 weeks after pegvaliase initiation), 11 out of 18 patients (61%) reached Phe levels below 600 μmol/l. Outcomes varied significantly across cases. All cases underscore the potential of pegvaliase in reducing Phe levels, enhancing the quality of life, and promoting social skills and independence. Additionally, the cases highlight the challenges associated with pegvaliase therapy, including managing adverse events and ensuring patient motivation and adherence.

CONCLUSION

This is the first report about the Italian experience of managing patients affected by PKU with pegvaliase. Given the limited real-world data on the use of pegvaliase in PKU management, this case series offers valuable insights into the practical implementation and management of pegvaliase therapy in this Country. Continued research and data collection will be crucial to confirm and progress with this treatment. Despite potential challenges, pegvaliase therapy represents a substantial promise in managing PKU in Italy. Patient education, personalized treatment approaches, and careful monitoring are important to ensure optimal patient outcomes.

Complete correction of murine phenylketonuria by selection-enhanced hepatocyte transplantation

BACKGROUND AND AIMS

Hepatocyte transplantation for genetic liver diseases has several potential advantages over gene therapy. However, the low efficiency of cell engraftment has limited its clinical implementation. This problem could be overcome by selectively expanding transplanted donor cells until they replace enough of the liver mass to achieve therapeutic benefit. We previously described a gene therapy method to selectively expand hepatocytes deficient in cytochrome p450 reductase (Cypor) using acetaminophen (APAP). Because Cypor is required for the transformation of APAP to a hepatotoxic metabolite, Cypor-deficient cells are protected from toxicity and are able to expand following APAP-induced liver injury. Here, we apply this selection system to correct a mouse model of phenylketonuria by cell transplantation.

APPROACH AND RESULTS

Hepatocytes from a wild-type donor animal were edited in vitro to create Cypor deficiency and then transplanted into phenylketonuric animals. Following selection with APAP, blood phenylalanine concentrations were fully normalized and remained stable following APAP withdrawal. Cypor-deficient hepatocytes expanded from < 1% to ~14% in corrected animals, and they showed no abnormalities in blood chemistries, liver histology, or drug metabolism.

CONCLUSIONS

We conclude that APAP-mediated selection of transplanted hepatocytes is a potential therapeutic for phenylketonuria with long-term efficacy and a favorable safety profile.

Does hyperphenylalaninemia induce brain glucose hypometabolism? Cerebral spinal fluid findings in treated adult phenylketonuric patients

Despite numerous studies in human patients and animal models for phenylketonuria (PKU; OMIM#261600), the pathophysiology of PKU and the underlying causes of brain dysfunction and cognitive problems in PKU patients are not well understood. In this study, lumbar cerebral spinal fluid (CSF) was obtained immediately after blood sampling from early-treated adult PKU patients who had fasted overnight. Metabolite and amino acid concentrations in the CSF of PKU patients were compared with those of non-PKU controls. The CSF concentrations and CSF/plasma ratios for glucose and lactate were found to be below normal, similar to what has been reported for glucose transporter1 (GLUT1) deficiency patients who exhibit many of the same clinical symptoms as untreated PKU patients. CSF glucose and lactate levels were negatively correlated with CSF phenylalanine (Phe), while CSF glutamine and glutamate levels were positively correlated with CSF Phe levels. Plasma glucose levels were negatively correlated with plasma Phe concentrations in PKU subjects, which partly explains the reduced CSF glucose concentrations. Although brain glucose concentrations are unlikely to be low enough to impair brain glucose utilization, it is possible that the metabolism of Phe in the brain to produce phenyllactate, which can be transported across the blood-brain barrier to the blood, may consume glucose and/or lactate to generate the carbon backbone for glutamate. This glutamate is then converted to glutamine and carries the Phe-derived ammonia from the brain to the blood. While this mechanism remains to be tested, it may explain the correlations of CSF glutamine, glucose, and lactate concentrations with CSF Phe.

Benefits of a prolonged-release amino acid mixture in four pregnant women with phenylketonuria

Background: Maternal phenylketonuria (mPKU) is a pathologic condition occurring in the fetus of a mother with PKU that is caused by prolonged elevated intrauterine blood phenylalanine (Phe) levels, which can lead to congenital abnormalities and mental retardation of newborns. Management of PKU during pregnancy can be challenging as protein substitutes may exacerbate nausea, vomiting, and gastrointestinal symptoms. Aim: To report the successful management of four PKU pregnant women. Methods: The patients were administered with prolonged-release amino acid supplementation and were recommended to follow a strict diet. Blood Phe concentration, adherence to diet, and occurrence of adverse events were monitored. Results: All patients achieved safe levels of blood Phe concentration (120-360 µmol/L) since preconception and during pregnancy (mean Phe concentration values of 143.34 ± 137.59, 226.48 ± 194.57, 186.68 ± 133.67, and 187.47 ± 42.59 µmol/L). During the first trimester of pregnancy, all patients manifested gastrointestinal symptoms such as nausea, gastrointestinal reflux, and abdominal bloating, which were managed by either changing protein substitute or extending the time window between different meals and amino acid mixtures administration. The four women continued their pregnancies without experiencing further complications and delivered neonates with normal growth parameters and no malformations. Conclusion: Findings of this case series suggest that the intake of a prolonged-release amino acid mixture in granules is well tolerated by pregnant PKU patients, eventually leading to good metabolic control and fetal growth within normal ranges.

Cognition after a 4-week high phenylalanine intake in adults with phenylketonuria - a randomized controlled trial

BACKGROUND

Phenylketonuria (PKU) is an autosomal recessive metabolic disorder characterized by increased phenylalanine (Phe) concentrations in the blood and brain. Despite wide agreement on treatment during childhood, recommendations for adults are still controversial.

OBJECTIVE

To assess the impact of a 4-week increase in Phe intake (simulating normal dietary Phe consumption) on cognition, mood, and depression in early-treated adults with PKU in a double-blind, randomized controlled trial (RCT).

METHODS

In a single-site crossover trial, 30 adult patients with classical PKU diagnosed at birth were recruited. All patients underwent a 4-week period of oral Phe administration (1500-3000 mg Phe/d) and a 4-week placebo period in a randomly assigned order with age, sex, and place of usual medical care as stratification factors. Analyses were based on the intention-to-treat (ITT) and per protocol (PP) approach to claim noninferiority (noninferiority margin -4%), with working memory accuracy as the primary endpoint and additional cognitive domains, mood, and depression as secondary endpoints.

RESULTS

For the primary endpoint, a 4-week increase of Phe intake was noninferior to placebo with respect to working memory accuracy in both the ITT [point estimate 0.49; lower limit 95% confidence interval (CI): -1.99] and the PP analysis (point estimate -1.22; lower limit 95% CI: -2.60). Secondary outcomes (working memory reaction time, manual dexterity, mood, and depression) did not significantly differ between the Phe and placebo period, except for sustained attention (point estimate 31.0; lower limit 95% CI: 9.0). Adverse events were more frequent during the Phe than during the placebo period (95% CI: 1.03, 2.28, P = 0.037).

CONCLUSIONS

In early-treated adult patients with PKU, a 4-week high Phe intake was noninferior to continuing Phe restriction regarding working memory accuracy, and secondary outcomes did not differ except for sustained attention. Longer-term RCTs are required to determine whether low Phe levels need to be maintained throughout different periods of adulthood. This trial was registered at the clinicaltrials.gov as NCT03788343.

First successful outcomes of pegvaliase (PALYNZIQ) in children

BACKGROUND

PKU is an autosomal recessive hereditary inborn error of metabolism caused by a lack of phenylalanine hydroxylase enzyme activity. Pegvaliase (PALYNZIQ®) treatment has been approved to reduce blood Phe concentrations in adult phenylketonuria patients with uncontrolled blood Phe concentrations greater than 600 micromol/L on current management. However, data regarding individuals under the age of 16 is still unavailable.

CASE REPORT

We report a 12-year-old Saudi girl who underwent pegvaliase therapy and was closely monitored for one year. Remarkably, a positive therapeutic response became apparent six months after commencing pegvaliase treatment. Phenylalanine (Phe) levels showed significant improvement, stabilising within the < 5 to 14 µmol/L range on a regular diet without any restriction. At her current age of 12, the patient maintains an unrestricted dietary regimen, consuming a diverse selection of foods, including poultry, meat, and protein sources, all while consistently maintaining normal Phe levels with no change in mental status after treatment. The parents gave their written, informed consent in allowing the research study to be carried out and clinical data to be published.

CONCLUSIONS

This report addresses the potential broader applications of Pegvaliase in children, as well as its safety and tolerability in this age group. However, larger sample sizes and robust methodologies are required to validate such findings.

Efficacy and safety of sapropterin before and during pregnancy: Final analysis of the Kuvan® Adult Maternal Paediatric European Registry (KAMPER) maternal and Phenylketonuria Developmental Outcomes and Safety (PKUDOS) PKU-MOMs sub-registries

Infants born to mothers with phenylketonuria (PKU) may develop congenital abnormalities because of elevated phenylalanine (Phe) levels in the mother during pregnancy. Maintenance of blood Phe levels between 120 and 360 μmol/L reduces risks of birth defects. Sapropterin dihydrochloride helps maintain blood Phe control, but there is limited evidence on its risk-benefit ratio when used during pregnancy. Data from the maternal sub-registries-KAMPER (NCT01016392) and PKUDOS (NCT00778206; PKU-MOMs sub-registry)-were collected to assess the long-term safety and efficacy of sapropterin in pregnant women in a real-life setting. Pregnancy and infant outcomes, and the safety of sapropterin were assessed. Final data from 79 pregnancies in 57 women with PKU are reported. Sapropterin dose was fairly constant before and during pregnancy, with blood Phe levels maintained in the recommended target range during the majority (82%) of pregnancies. Most pregnancies were carried to term, and the majority of liveborn infants were reported as 'normal' at birth. Few adverse and serious adverse events were considered related to sapropterin, with these occurring in participants with high blood Phe levels. This report represents the largest population of pregnant women with PKU exposed to sapropterin. Results demonstrate that exposure to sapropterin during pregnancy was well-tolerated and facilitated maintenance of blood Phe levels within the target range, resulting in normal delivery. This critical real-world data may facilitate physicians and patients to make informed treatment decisions about using sapropterin in pregnant women with PKU and in women of childbearing age with PKU who are responsive to sapropterin.

Maximal dietary responsiveness after tetrahydrobiopterin (BH4) in 19 phenylalanine hydroxylase deficiency patients: What super-responders can expect

Background

Inherited phenylalanine hydroxylase deficiency, also known as phenylketonuria (PKU), causes poor growth and neurologic deficits in the untreated state. After ascertainment through newborn screen and dietary phenylalanine (Phe) restriction to achieve plasma Phe in the range of 120-360 μmol/L, these disease manifestations can be prevented. Poor compliance with protein restricted diets supported by medical food is typical in later years, beginning in the late toddler and teenage years. Pharmacologic doses of oral tetrahydrobiopterin (BH4; sapropterin dihydrochloride) is effective in reducing plasma Phe in about 40-50% of PKU patients but effectiveness is highly variable.

Objective

To assess the maximal responsiveness to 20 mg/kg/day oral BH4 as it affects plasma Phe and dietary Phe allowance in PKU patients.

Materials and methods

This was a single-center, retrospective observational study, combining case reports of individual patients. We reported an outcome of 85 patients with PKU who were trialed on BH4. Phe levels and dietary records of 19 BH4 "super-responders" were analyzed.

Results

Overall, 63.5% of the patients (54/85) were considered BH4 responders. However, we quantitated the dietary liberalization of 19 of our responsive patients (35%), those with at least a 2-fold increase in dietary Phe and maintenance of plasma Phe in treatment range. In these "super-responders", the mean plasma Phe at baseline was 371 ± 237 μmol/L and decreased to 284 ± 273 μmol/L after 1 year on BH4. Mean dietary Phe tolerance increased significantly from 595 ± 256 to 2260 ± 1414 mg/day (p ≤0.0001), while maintaining mean plasma Phe levels within treatment range. Four patients no longer required dietary Phe restriction and could discontinue medical food. The majority of patients had at least one BH4-responsive genotype.

Conclusion

This cohort demonstrates the maximally achievable dietary liberalization which some PKU patients may expect with BH4 therapy. Health benefits are considered to accrue in patients with increased intact protein.

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.

Outcomes in 14 live births resulting from Pegvaliase-treated pregnancies in PKU-affected females

BACKGROUND

Adults with PKU have difficulty maintaining plasma phenylalanine (Phe) in the range that is safe for neurologic function. Elevated plasma Phe is a risk factor for congenital anomalies and developmental delay in offspring resulting from pregnancies with poor Phe control in women with PKU. Enzyme supplementation with pegvaliase allows adults with PKU to eat an unrestricted diet and have plasma Phe levels in a safe range for pregnancy but pegvaliase has not been approved for use in pregnant females with PKU. We report the results of chart review of 14 living offspring of females affected with PKU who were responsive to pegvaliase and chose to remain on pegvaliase throughout their pregnancy.

METHODS

Fourteen pregnancies (one triplet pregnancy) and their offspring were identified at eight PKU treatment centers and medical records from pregnancy and birth were submitted for this study. Institutional Review Board approval was obtained. Responses to a dataset were provided to a single center and analyzed.

RESULTS

Six females and eight males were born without congenital anomalies and all offspring had normal growth parameters. While mothers had preexisting comorbidities, no additional comorbidities were reported in the offspring. Four of eleven infants (excluding triplet pregnancies) were delivered preterm (36%), a higher rate than the general population (12%). A single first trimester (eight weeks) miscarriage in a 40y was not counted in this cohort of 14 live born infants.

CONCLUSION

This retrospective study suggests that pegvaliase is effective at maintaining safe maternal blood Phe levels during pregnancy without deleterious effects on mother or child. A tendency toward premature birth (4/11; 36%) is higher than expected.

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.

Construction of an ultrasensitive dual-mode chiral molecules sensing platform based on molecularly imprinted polymer modified bipolar electrode

Chiral molecules are abundant in nature. Phenylketonuria (PKU) is caused by the abnormal transformation of chiral molecules L-phenylalanine (L-Phe) in the human blood, which can cause irreversible harm to the human body. In this work, we documented an electrochemiluminescent (ECL) dual-mode sensor platform based on molecularly imprinted polymer (MIP) modified closed bipolar electrodes for high sensitivity detection of L-Phe and D-phenylalanine (D-Phe). In the anode chamber of a bipolar electrode modified with phenylalanine imprinting, Ru (bpy)32+ underwent a redox reaction to produce a chemiluminescence response under the stimulation of a driving voltage. At the same time, the reduction of the cathode film of the bipolar electrode was promoted, and the color changed from dark blue to nearly white. Thus, the dual-mode detection of target molecules is realized. The detection range of the sensor for phenylalanine reached 0.01-10,000 nM, and the detection limits of L-Phe and D-Phe were 3.9 pM and 4.6 pM (S/N = 3), respectively. This dual-mode system achieved high stability and high specificity, and also successfully realized the detection of actual samples, which is expected to achieve future clinical applications.

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.

The value of waist circumference as a preditor of cardiovascular risk in adult patients with classic phenylketonuria

BACKGROUND AND AIMS

We aimed to evaluate the differences in some cardiovascular risk (CVR) factors between adult patients without and with phenylketonuria (PKU) and to explore the correlation between waist circumference (WC) and body mass index (BMI) with the previous variables.

METHODS

This was an observational case-control study that included patients older than 18 years with a diagnosis of classic PKU. The controls were age- and sex-matched individuals. We collected demographic, epidemiological, clinical, and laboratory variables, including WC, BMI, and lipid profile parameters.

RESULTS

A total of 72 patients (25 controls and 47 cases) were included with a mean age of 36 years, of which 45 (62%) were women. Adult PKU patients showed lower high-density lipoprotein cholesterol (HDL-c) and higher triglyceride (TG) levels than the control group. We found an association between WC and uric acid (B=0.024, P=0.013, 95%CI: 0.005-0.043), TG (B=0.768, P=0.024, 95%CI: 0.107-1.428), and HDL-c (B=-0.254, P=0.026, 95%CI: -0.477 to (-0.032)) levels in PKU patients. However, we did not find any trend between WC and uric acid, TG and HDL-c levels that reached statistical significance (P<0.05) in patients without PKU.

CONCLUSIONS

Waist circumference rather than BMI may better represent the CVR in patients with PKU.

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.

Relationship satisfaction in adults with phenylketonuria is positively associated with following recommended treatment, having a partner involved in management, and maintaining good health

RATIONALE

Phenylketonuria (PKU) is a metabolic condition that requires treatment for life. There is increasing evidence that chronic illnesses put strain on relationships and marriages. However, no studies have examined the unique factors that metabolic conditions have on affected individuals and their relationship satisfaction. We surveyed a population of adult patients with PKU and assessed how management, treatment, and lifestyle factors impact their relationship satisfaction.

PURPOSE

The purpose of our study was to explore whether factors such as involvement of partner in PKU management, impact of challenges unique to PKU (e.g., diet, family planning, mood disturbances), and PKU treatment types were associated with the degree of relationship satisfaction.

METHOD

We surveyed adult patients with PKU (n = 82) who were either currently in or had previously been in a long-term relationship. We developed a 78-question survey that included unique questions regarding lifestyle, treatment, and management of their PKU in addition to a validated Relationship Assessment Score. Questions included single choice, multiple choice, and 3 open-ended questions.

RESULTS

We found that higher relationship satisfaction was associated with increased partner involvement, increased health, and adherence to recommended PKU treatments. Participants utilizing both diet and pharmaceutical treatment had the highest relationship satisfaction. Finally, participants who reported that their PKU did not contribute to the ending of a previous relationship reported higher relationship satisfaction scores.

CONCLUSION

This study suggests that involvement of partners in the management and treatment of a chronic illness and adherence to recommended treatments can significantly improve relationship satisfaction.

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.

Total Protein Intake in Patients with PKU: Adequacy Evaluation According to the European PKU Guidelines from 2017

In PKU, the protein requirements are contentious. In 2018, we evaluated the protein intake in patients with PKU. Ninety-nine early treated patients aged 19.3 ± 8.2 years (54% males) were studied. A total of 24 had hyperphenylalaninemia (HPA), 48 mild and 27 classical PKU. All had an annual nutritional status evaluation. A total of 83% were on diet therapy only, and 17% were on diet with tetrahydrobiopterin therapy. Anthropometry, metabolic control and nutritional intake [total protein (TP, g/kg), natural protein (NP, g/kg), protein equivalent from protein substitutes (PE, g/kg)] were collected. TP adequacy (TPA) was calculated as a % of WHO (2007) safe levels of protein intake. Results were compared with the European PKU Guidelines (EPG). The median % contribution NP of TP intake was 53% [31-100]. Most patients (78%) had a TP intake above the EPG recommendations. The median TPA was 171% [146-203], with 79% [51-165] from NP and 84% [0-109] from PE. A TPA of 100-140% was observed in 16 (16%) patients. Only n = 6 (6%) patients had a TPA < 100%. These results emphasize the heterogeneity of PKU. More research is needed to understand the necessity of a single protein recommendation for all, as a 'one-size-fits-all' solution might not be appropriate.

New challenges in management of phenylketonuria in pregnancy: a case report

BACKGROUND

Phenylketonuria (PKU) is an autosomal recessive disease that belongs to a group of disorders resulting from inborn errors of protein metabolism. It was the first disease included in neonatal screening. Neonatal screening has allowed an early diagnosis and treatment of the disease. As a result, an increasing number of women diagnosed with phenylketonuria have reached the reproductive phase of life in good health, and management of pregnancy in women with PKU is becoming more frequent.

CASE PRESENTATION

In this study, we report the case of a 28-year-old Caucasian patient being followed up for phenylketonuria at Ramón y Cajal Hospital's Metabolic Diseases Unit. We describe the patient's gestation, impacted by her and her partner's diagnosis of PKU, classic and mild phenotypes, respectively, resulting in the fetus affectation.

CONCLUSIONS

The description of PKU management-diagnosis, follow-up, and treatment-for both that of patient and that of the gestation with fetus affectation covers a wide sample scenario that shows the effectiveness of pregnancy planning and monitoring of females with PKU and questions the need to carry out a genetic study of gene PKU in the study of fertility.

The treatment of biochemical genetic diseases: From substrate reduction to nucleic acid therapies

Newborn screening (NBS) began a revolution in the management of biochemical genetic diseases, greatly increasing the number of patients for whom dietary therapy would be beneficial in preventing complications in phenylketonuria as well as in a few similar disorders. The advent of next generation sequencing and expansion of NBS have markedly increased the number of biochemical genetic diseases as well as the number of patients identified each year. With the avalanche of new and proposed therapies, a second wave of options for the treatment of biochemical genetic disorders has emerged. These therapies range from simple substrate reduction to enzyme replacement, and now ex vivo gene therapy with autologous cell transplantation. In some instances, it may be optimal to introduce nucleic acid therapy during the prenatal period to avoid fetopathy. However, as with any new therapy, complications may occur. It is important for physicians and other caregivers, along with ethicists, to determine what new therapies might be beneficial to the patient, and which therapies have to be avoided for those individuals who have less severe problems and for which standard treatments are available. The purpose of this review is to discuss the "Standard" treatment plans that have been in place for many years and to identify the newest and upcoming therapies, to assist the physician and other healthcare workers in making the right decisions regarding the initiation of both the "Standard" and new therapies. We have utilized several diseases to illustrate the applications of these different modalities and discussed for which disorders they may be suitable. The future is bright, but optimal care of the patient, including and especially the newborn infant, requires a deep knowledge of the disease process and careful consideration of the necessary treatment plan, not just based on the different genetic defects but also with regards to different variants within a gene itself.

Inborn errors of amino acid metabolism - from underlying pathophysiology to therapeutic advances

Amino acids are organic molecules that serve as basic substrates for protein synthesis and have additional key roles in a diverse array of cellular functions, including cell signaling, gene expression, energy production and molecular biosynthesis. Genetic defects in the synthesis, catabolism or transport of amino acids underlie a diverse class of diseases known as inborn errors of amino acid metabolism. Individually, these disorders are rare, but collectively, they represent an important group of potentially treatable disorders. In this Clinical Puzzle, we discuss the pathophysiology, clinical features and management of three disorders that showcase the diverse clinical presentations of disorders of amino acid metabolism: phenylketonuria, lysinuric protein intolerance and homocystinuria due to cystathionine β-synthase (CBS) deficiency. Understanding the biochemical perturbations caused by defects in amino acid metabolism will contribute to ongoing development of diagnostic and management strategies aimed at improving the morbidity and mortality associated with this diverse group of disorders.

Towards precision medicine for phenylketonuria: The effect of restoring a strict metabolic control in adult patients with early-treated phenylketonuria

BACKGROUND AND OBJECTIVE

Neonatal screening and early treatment have changed the natural history of PKU, preventing severe neurological and intellectual disability. Nevertheless, the outcome of the disease in early-treated adult patients (ETPKU) is less than optimal, the predictive value of metabolic biomarkers is feeble, and the recommended levels of blood phenylalanine (Phe) for adulthood are controversial. A crucial question whose answer will improve our understanding and treatment of PKU is whether cognitive outcomes can be modulated by levels of Phe even in early-treated adults. To address this question, we carried out an interventional study in seven ETPKU women planning a pregnancy.

METHODS

They underwent an extensive neurocognitive assessment at baseline, and 3 and 6 months after having attained the blood Phe concentration recommended to prevent PKU fetopathy, but before pregnancy.

RESULTS

After 3 and 6 months with a stable blood Phe level of about 240 μmol/L, all participants experienced significant improvements in almost all neurocognitive domains and tasks. IQ also increased of 11 to 21 points from the last assessment before enrolment. This pattern remained strong and consistent after correction for multiple comparisons.

CONCLUSION

Our results indicate that a) strong cognitive improvement is possible even in adulthood and may be demonstrated by lowering Phe near normal levels; b) testing cognition under different metabolic conditions may unveil an individual vulnerability to Phe. These results pave the way for personalised treatment of the disease in adults with ETPKU.

Predictors of eventual requirement of phenylalanine-restricted diet in young infants with phenylalanine hydroxylase deficiency initially managed with sapropterin monotherapy

BACKGROUND

Phenylalanine (Phe)-restricted diet is associated with lower quality of life for patients with phenylketonuria (PKU), and a concern for caregivers of recently-diagnosed infants. Sapropterin is an oral drug used as an alternative or adjunct to dietary treatment. We have observed that some of the young infants initially managed successfully with sapropterin monotherapy have required dietary treatment in long-term follow-up. We aimed to determine the baseline factors associated with future initiation of dietary treatment in these patients.

METHODS

Data were obtained retrospectively from the medical records of 80 PKU patients started on sapropterin monotherapy before 3 months of age between 2011 and 2021.

RESULTS

The patients were followed for a median of 3.9 years (Q1-Q3: 2.5-5.75 years). Sapropterin was tapered down and discontinued in 5 patients (6.3%) as their Phe levels remained below 360 μmol/L without treatment. Sapropterin monotherapy was sufficient in 62 patients (77.5%), while 13 (16.2%) required dietary treatment. Phe and tyrosine (Tyr) levels, and Phe:Tyr ratios differed significantly among the patients maintained on sapropterin monotherapy and those started on dietary treatment, but the Phe:Tyr ratio at diagnosis was the most important independent baseline variable (OR: 1.61, 95% CI: 1.15-2.27, p = 0.006), with Phe:Tyr ratio at diagnosis >5.25 associated with dietary treatment (sensitivity: 90.0%, specificity: 81.8%). Genotypic phenotype value (GPV), unavailable at baseline, was also associated with dietary treatment (median GPV 9.2 vs. 3.8, p = 0.006), but some genotypes were not specific to the final treatment modality.

DISCUSSION

We propose that the Phe:Tyr ratio at diagnosis is an important indicator to predict dietary requirement in young infants initially managed with sapropterin monotherapy.

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.

Harmonization of distributed multi-center analysis based on dried blood spot reference materials supporting the screening of neonatal inherited metabolic disorders

BACKGROUND

The standardization of quantification data is critical for ensuring the reliability and measurement traceability in the screening of neonatal inherited metabolic disorders. However, the availability of national certified reference materials is limited in China.

METHODS

In this study, we developed a series of dried blood spot (DBS) reference materials containing 9 amino acids (AA) and 10 acylcarnitines (AC) for neonatal screening. Four levels of the reference materials were measured with tandem mass spectrometry (MS/MS) by seven laboratories using different commercial In Vitro Diagnostic Device (IVD) kits. Then, 100 clinical samples were measured using both derivatization and non-derivatization methods by the same laboratory.

RESULTS

We found high homogeneity and stability at all levels of the reference materials, with the coefficient of variation (CV) of the analytes less than 15%. These reference materials can be used to assess the testing capabilities of different laboratories. Our test also revealed that the correction factors (CF) calculated by the reference materials, along with clinical samples, could increase the consistency for different kits.

CONCLUSION

The DBS reference materials proposed in this study provide reliability for the harmonization in multi-center analysis for the screening of neonatal inherited metabolic disorders. And applying our correction method for the screening could improve the data consistency of the DBS samples prepared by different methods.

Deubiquitinase USP19 enhances phenylalanine hydroxylase protein stability and its enzymatic activity

Phenylalanine hydroxylase (PAH) is the key enzyme in phenylalanine metabolism, deficiency of which is associated with the most common metabolic phenotype of phenylketonuria (PKU) and hyperphenylalaninemia (HPA). A bulk of PKU disease-associated missense mutations in the PAH gene have been studied, and the consequence of each PAH variant vary immensely. Prior research established that PKU-associated variants possess defects in protein folding with reduced cellular stability leading to rapid degradation. However, recent evidence revealed that PAH tetramers exist as a mixture of resting state and activated state whose transition depends upon the phenylalanine concentration and certain PAH variants that fail to modulate the structural equilibrium are associated with PKU disease. Collectively, these findings framed our understanding of the complex genotype-phenotype correlation in PKU. In the current study, we substantiate a link between PAH protein stability and its degradation by the ubiquitin-mediated proteasomal degradation system. Here, we provide an evidence that PAH protein undergoes ubiquitination and proteasomal degradation, which can be reversed by deubiquitinating enzymes (DUBs). We identified USP19 as a novel DUB that regulates PAH protein stability. We found that ectopic expression of USP19 increased PAH protein level, whereas depletion of USP19 promoted PAH protein degradation. Our study indicates that USP19 interacts with PAH and prevents polyubiquitination of PAH subsequently extending the half-life of PAH protein. Finally, the increase in the level of PAH protein by the deubiquitinating activity of USP19 resulted in enhanced metabolic function of PAH. In summary, our study identifies the role of USP19 in regulating PAH protein stability and promotes its metabolic activity. Graphical highlights 1. E3 ligase Cdh1 promotes PAH protein degradation leading to insufficient cellular amount of PAH causing PKU. 2. A balance between E3 ligase and DUB is important to regulate the proteostasis of PAH. 3. USP19 deubiquitinates and stabilizes PAH further protecting it from rapid degradation. 4. USP19 increases the enzymatic activity of PAH, thus maintaining normal Phe levels.

Efficacy and safety of a synthetic biotic for treatment of phenylketonuria: a phase 2 clinical trial

Despite available treatment options, many patients with phenylketonuria (PKU) cannot achieve target plasma phenylalanine (Phe) levels1. We previously modified Escherichia coli Nissle 1917 to metabolize Phe in the gut after oral administration (SYNB1618) and designed a second strain (SYNB1934) with enhanced activity of phenylalanine ammonia lyase2,3. In a 14-day open-label dose-escalation study (Synpheny-1, NCT04534842 ), we test a primary endpoint of change from baseline in labeled Phe (D5-Phe AUC0-24; D5-Phe area under the curve (AUC) over 24 hours after D5-Phe administration) in plasma after D5-Phe challenge in adult participants with screening Phe of greater than 600 µM. Secondary endpoints were the change from baseline in fasting plasma Phe and the incidence of treatment-emergent adverse events. A total of 20 participants (ten male and ten female) were enrolled and 15 completed the study treatment. Here, we show that both strains lower Phe levels in participants with PKU: D5-Phe AUC0-24 was reduced by 43% from baseline with SYNB1934 and by 34% from baseline with SYNB1618. SYNB1934 led to a decrease in fasting plasma Phe of 40% (95% CI, -52, -24). There were no serious adverse events or infections. Four participants discontinued because of adverse events, and one withdrew during the baseline period. We show that synthetic biotics can metabolize Phe in the gut, lower post-prandial plasma Phe levels and lower fasting plasma Phe in patients with PKU.

Long-Term Renal Function in Adult Patients with Phenylketonuria

INTRODUCTION

In phenylketonuria (PKU), toxic phenylalanine (Phe) can harm other organs beyond the brain. Furthermore, the lifelong therapy of PKU consists of consumption of increased amounts of amino-acid mixture that provoke hyperfiltration in the glomeruli. Therefore, the adherence to therapy in PKU might influence the long-term kidney function in PKU patients.

METHODS

Data from 41 adult, early treated PKU patients were analyzed in this 10-year, retrospective, monocentric study. Two subgroups were created according to their therapy adherence: one with long-term blood Phe levels in the therapeutic range (<600 µmol/L), and one with suboptimal blood Phe levels. Renal function and metabolic parameters were collected over 10 years. Kidney function parameters were compared between the two groups and associations between blood Phe levels and kidney function were tested.

RESULTS

After 10 years, serum creatinine levels (p = 0.369) and estimated glomerular filtration rate (eGFR) (p = 0.723) did not change significantly from baseline in the good therapeutic group. The suboptimal therapeutic group's eGFR decreased in the same period (from 110.4 ± 14 mL/min/1.73 m2 to 94.2 ± 16 mL/min/1.73 m2, p = 0.017). At 10 years, the suboptimal therapeutic group had an increased serum creatinine level (81 ± 14.4 μmol/L vs. 71.5 ± 13 μmol/L, p = 0.038), and a decreased eGFR (94.2 ± 16 mL/min/1.73 m2 vs. 103.3 ± 13 mL/min/1.73 m2p = 0.031) compared to the good adhering group. Significant negative correlation between Phe levels and eGFR (r = -0.41, p = 0.008) was observed.

CONCLUSION

Long-term suboptimal therapy adherence in PKU patients with high blood Phe levels may lead to deterioration in kidney function.

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.

Utilising the precision nutrition toolkit in the path towards precision medicine

The overall aim of precision nutrition is to replace the 'one size fits all' approach to dietary advice with recommendations that are more specific to the individual in order to improve the prevention or management of chronic disease. Interest in precision nutrition has grown with advancements in technologies such as genomics, proteomics, metabolomics and measurement of the gut microbiome. Precision nutrition initiatives have three major applications in precision medicine. First, they aim to provide more 'precision' dietary assessments through artificial intelligence, wearable devices or by employing omic technologies to characterise diet more precisely. Secondly, precision nutrition allows us to understand the underlying mechanisms of how diet influences disease risk and identify individuals who are more susceptible to disease due to gene-diet or microbiota-diet interactions. Third, precision nutrition can be used for 'personalised nutrition' advice where machine-learning algorithms can integrate data from omic profiles with other personal and clinical measures to improve disease risk. Proteomics and metabolomics especially provide the ability to discover new biomarkers of food or nutrient intake, proteomic or metabolomic signatures of diet and disease, and discover potential mechanisms of diet-disease interactions. Although there are several challenges that must be overcome to improve the reproducibility, cost-effectiveness and efficacy of these approaches, precision nutrition methodologies have great potential for nutrition research and clinical application.

Mutational landscape of phenylketonuria in Iran

To date more than 1000 different variants in the PAH gene have been identified in patients with phenylketonuria (PKU). In Iran, several studies have been performed to investigate the genetics bases of the PKU in different parts of the country. In this study, we have analysed and present an update of the mutational landscape of the PAH gene as well as the population genetics and frequencies of detected variants for each cohort. Published articles on PKU mutations in Iran were identified through a comprehensive PubMed, Google Scholar, Web of Science (ISI), SCOPUS, Elsevier, Wiley Online Library and SID literature search using the terms: "phenylketonuria", "hyperphenylalaninemia", and "PKU" in combination with "Iran", "Iranian population", "mutation analysis", and "Molecular genetics". Among the literature-related to genetics of PKU, 18 studies were on the PKU mutations. According to these studies, in different populations of Iran 1497 patients were included for mutation detection that resulted in detection of 129 different mutations. Results of genetic analysis of the different cohorts of Iranian PKU patients show that the most prevalent mutation in Iran is the pathogenic splice variant c.1066-11G > A, occurring in 19.54% of alleles in the cohort. Four other common mutations were p.Arg261Gln, p.Pro281Leu, c.168 + 5G > C and p.Arg243Ter (8.18%, 6.45%, 5.88% and 3.7%, respectively). One notable feature of the studied populations is its high rate of consanguineous marriages. Considering this feature, determining the prevalent PKU mutations could be advantageous for designing screening and diagnostic panels in Iran.

Influence of blood phenylalanine level variations on the development of executive functions and social cognition in children with phenylketonuria

OBJECTIVE

To investigate the performance of 27 children with phenylketonuria (PKU) in tests of Executive Functions (EF) and Social Cognition (SC), and their associations with metabolic control inferred by phenylalanine (Phe) levels.

METHODS

The PKU group was dichotomized according to baseline Phe-levels into; "classical PKU"(n = 14), with Phe-levels above 1200 μmol/L (> 20 mg/dL); and "mild PKU" (n = 13) with Phe-between 360 and 1200 μmol/L (6-20 mg/dL). The neuropsychological assessment focused on the EF and SC subtests of the NEPSY-II battery and intellectual performance. Children were compared to age-matched healthy participants.

RESULTS

Participants with PKU presented significantly lower Intellectual Quotient (IQ) compared to controls (p = 0.001). Regarding EF analysis adjusted by age and IQ, significant differences between groups were observed only in the executive attention subtests (p = 0.029). The SC set of variables was significantly different between groups (p = 0.003), as in the affective recognition task (p < 0.001). In the PKU group, the relative variation of Phe-achieved 32.1 ± 21.0%. Relative Phe-variation was correlated only with measures of Working Memory (p < 0.001), Verbal Fluency (p = 0.004), Inhibitory Control (p = 0.035) and Theory of Mind (p = 0.003).

CONCLUSIONS

Phonological Verbal Fluency, Working Memory, Inhibitory Control, and Theory of Mind were shown to be most vulnerable when there is non-ideal metabolic control. Variations in the level of Phe-may have a selective negative effect on Executive Functions and Social Cognition, but not on intellectual performance.

Classical phenylketonuria presenting as maternal PKU syndrome in the offspring of an intellectually normal woman

Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism resulting from a deficiency of phenylalanine hydroxylase (PAH). If untreated by dietary restriction of phenylalanine intake, impaired postnatal cognitive development results from the neurotoxic effects of excessive phenylalanine (Phe). Signs and symptoms include severe intellectual disability and behavior problems with a high frequency of seizures and variable microcephaly. Maternal PKU syndrome refers to fetal damage resulting in congenital abnormalities when the mother has untreated PKU during pregnancy. Here, we report an intellectually normal 32-year-old female who presented with recurrent pregnancy loss and two neonatal deaths with congenital heart disease, microcephaly, intrauterine growth restriction, and respiratory distress. She was diagnosed with PKU through exome sequencing performed for carrier testing with a homozygous pathogenic variant in the PAH gene, c.169_171del, p.(Glu57del) that is associated with classical PKU. Consistent with the genetic finding, she had a markedly increased plasma phenylalanine concentration of 1642 μmol/L (normal <100). This case demonstrates that recurrent pregnancy loss due to untreated maternal PKU may present as an initial finding in otherwise unsuspected classical PKU and illustrates that extreme degrees of variable expressivity may occur in classical PKU. Moreover, this case illustrates the value of genomic sequencing of women who experience recurrent pregnancy loss or neonatal anomalies.