Protein Substitutes in PKU; Their Historical Evolution

Current Advances and Material Innovations in the Search for Novel Treatments of Phenylketonuria

Phenylketonuria (PKU) is a genetically inherited disease caused by a mutation of the gene encoding phenylalanine hydroxylase (PAH) and is the most common inborn error of amino acid metabolism. A deficiency of PAH leads to increased blood and brain levels of phenylalanine (Phe), which may cause permanent neurocognitive symptoms and developmental delays if untreated. Current management strategies for PKU consist of early detection through neonatal screening and implementation of a restrictive diet with minimal amounts of natural protein in combination with Phe-free supplements and low-protein foods to meet nutritional requirements. For milder forms of PKU, oral treatment with synthetic sapropterin (BH4), the cofactor of PAH, may improve metabolic control of Phe and allow for more natural protein to be included in the patient's diet. For more severe forms, daily injections of pegvaliase, a PEGylated variant of phenylalanine ammonia-lyase (PAL), may allow for normalization of blood Phe levels. However, the latter treatment has considerable drawbacks, notably a strong immunogenicity of the exogenous enzyme and the attached polymeric chains. Research for novel therapies of PKU makes use of innovative materials for drug delivery and state-of-the-art protein engineering techniques to develop treatments which are safer, more effective, and potentially permanent.

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.

Quality of Life in Patients with Phenylketonuria: A Systematic Review

The impact of phenylketonuria (PKU) on Quality of life (QoL) has been a topic of interest in recent research. This article reviews current researches on the impact of PKU on QoL. The review examines factors that may influence QoL, such as age, metabolic control, and treatment adherence. In this systematic review study, relevant articles were identified using a search strategy built with the keywords phenylketonuria, PKU, or hyperphenylalaninemia (or their synonyms) and QoL in Web of Science, Scopus, and PubMed databases. After identifying the articles, duplicates, reviews, scientific abstracts, articles published in languages other than English, and non relevant studies were excluded. The search strategy identified 951 records from databases, and after excluding duplicates, irrelevant studies, and those published in non English languages, 26 records were left that contained data on 1816 patients with PKU/hyperphenylalaninemia. The studies included both children/adolescents and adults. Overall, the studies found that the QoL of PKU patients was comparable to normative data, but some aspects such as emotional health and school functioning were lower. Metabolic control was found to significantly correlate with QoL. Younger patients and men had better QoL in several studies, while late treated patients and those with lower education had worse outcomes. It is concluded that QOL in patients with PKU is similar to the general population. However, given the chronic nature of the condition, it is important to pay special attention to their QoL. Poor QOL is associated with female gender, lower education, older age, and poor metabolic control.

Management of phenylketonuria in European PKU centres remains heterogeneous

Phenylketonuria (PKU) is a genetic disorder that follows an autosomal recessive inheritance pattern. Dietary treatment is the cornerstone of therapy and is based on natural protein restriction, Phe-free L-amino acid supplements (protein substitutes) and low protein foods. The aim of this project was to collect information about the clinical management of patients with PKU, focusing on understudied or unresolved issues such as blood phenylalanine (Phe) fluctuations and clinical symptoms, particularly gastro intestinal (GI) discomfort and sleep problems. The survey consisted of 10 open-ended and 12 multiple-choice questions that collected information about size of the PKU population in each center, the center's clinical practices and the outcomes observed by the center concerning adherence, clinical and biochemical abnormalities and clinical symptoms (GI and sleep). The questionnaire was sent to 72 experts from metabolic centers in 11 European countries. Thirty-three centers answered. The results of this survey provide information about the clinical practice in different age groups, concentrating on dietary tolerance, treatment adherence, and metabolic control. All the centers prescribed a Phe-restricted diet, with Phe-free/low Phe protein substitutes and low protein foods. Daily doses given of protein substitutes varied from 1 to 5, with adherence to the prescribed amounts decreasing with increasing age. Respondents identified that improvement in the flavor, taste, volume and smell of protein substitutes may improve adherence. Finally, the survey showed that clinical symptoms, such as GI discomfort and sleep problems occur in patients with PKU but are not systematically evaluated. Twenty-four-hour Phe fluctuations were not routinely assessed. The results highlight a strong heterogeneity of approach to management despite international PKU guidelines. More clinical attention should be given to gastrointestinal and sleep problems in PKU.

Body Composition Evaluation and Clinical Markers of Cardiometabolic Risk in Patients with Phenylketonuria

Cardiovascular diseases are the main cause of mortality worldwide. Patients with phenylketonuria (PKU) may be at increased cardiovascular risk. This review provides an overview of clinical and metabolic cardiovascular risk factors, explores the connections between body composition (including fat mass and ectopic fat) and cardiovascular risk, and examines various methods for evaluating body composition. It particularly focuses on nutritional ultrasound, given its emerging availability and practical utility in clinical settings. Possible causes of increased cardiometabolic risk in PKU are also explored, including an increased intake of carbohydrates, chronic exposure to amino acids, and characteristics of microbiota. It is important to evaluate cardiovascular risk factors and body composition in patients with PKU. We suggest systematic monitoring of body composition to develop nutritional management and hydration strategies to optimize performance within the limits of nutritional therapy.

Dietary Inflammatory Potential in Pediatric Diseases: A Narrative Review

Inflammatory status is one of the main drivers in the development of non-communicable diseases (NCDs). Specific unhealthy dietary patterns and the growing consumption of ultra-processed foods (UPFs) may influence the inflammation process, which negatively modulates the gut microbiota and increases the risk of NCDs. Moreover, several chronic health conditions require special long-term dietary treatment, characterized by altered ratios of the intake of nutrients or by the consumption of disease-specific foods. In this narrative review, we aimed to collect the latest evidence on the pro-inflammatory potential of dietary patterns, foods, and nutrients in children affected by multifactorial diseases but also on the dietetic approaches used as treatment for specific diseases. Considering multifactorial diet-related diseases, the triggering effect of pro-inflammatory diets has been addressed for metabolic syndrome and inflammatory bowel diseases, and the latter for adults only. Future research is required on multiple sclerosis, type 1 diabetes, and pediatric cancer, in which the role of inflammation is emerging. For diseases requiring special diets, the role of single or multiple foods, possibly associated with inflammation, was assessed, but more studies are needed. The evidence collected highlighted the need for health professionals to consider the entire dietary pattern, providing balanced and healthy diets not only to permit the metabolic control of the disease itself, but also to prevent the development of NCDs in adolescence and adulthood. Personalized nutritional approaches, in close collaboration between the hospital, country, and families, must always be promoted together with the development of new methods for the assessment of pro-inflammatory dietary habits in pediatric age and the implementation of telemedicine.

Micronutrient Deficiency in Inherited Metabolic Disorders Requiring Diet Regimen: A Brief Critical Review

Many inherited metabolic disorders (IMDs), including disorders of amino acid, fatty acid, and carbohydrate metabolism, are treated with a dietary reduction or exclusion of certain macronutrients, putting one at risk of a reduced intake of micronutrients. In this review, we aim to provide available evidence on the most common micronutrient deficits related to specific dietary approaches and on the management of their deficiency, in the meanwhile discussing the main critical points of each nutritional supplementation. The emerging concepts are that a great heterogeneity in clinical practice exists, as well as no univocal evidence on the most common micronutrient abnormalities. In phenylketonuria, for example, micronutrients are recommended to be supplemented through protein substitutes; however, not all formulas are equally supplemented and some of them are not added with micronutrients. Data on pyridoxine and riboflavin status in these patients are particularly scarce. In long-chain fatty acid oxidation disorders, no specific recommendations on micronutrient supplementation are available. Regarding carbohydrate metabolism disorders, the difficult-to-ascertain sugar content in supplementation formulas is still a matter of concern. A ketogenic diet may predispose one to both oligoelement deficits and their overload, and therefore deserves specific formulations. In conclusion, our overview points out the lack of unanimous approaches to micronutrient deficiencies, the need for specific formulations for IMDs, and the necessity of high-quality studies, particularly for some under-investigated deficits.

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.

Glycomacropeptide (GMP) rescued the oxidative and inflammatory activity of free L-AAs in human Caco-2 cells: New insights that support GMP as a valid and health-promoting product for the dietary management of phenylketonuria (PKU) patients

Phenylketonuria represents the most prevalent inborn error of amino acid metabolism. In early diagnosed patients adequate and continued dietary treatment results in a good neurologic outcome. However, due to the natural protein and phenylalanine-restricted diet, oxidative stress represents a concern in phenylketonuric patients. Clear evidences suggest that the pathophysiology of PKU is also dependent by mitochondrial impairment and oxidative stress. In this context due to the tight connection between oxidative and inflammatory stress and noncommunicable diseases (NCDs) development, it is reasonable to hypothesize that PKU patients may present a higher risk to develop NCDs during their life. Currently available protein substitutes on the market include free amino acids (L-AAs), prolonged-release protein substitute and formula containing glycomacropeptide (GMP). Our results suggest that free L-AAs significanlty worsens the intestinal hydrogen peroxide (H2O2) and lipopolysaccharides (LPS)-induced oxidative and inflammatory status in Caco-2 cells, which are significantly restored towards physiological condition by GMP alone and when present in a 1:1 mixture with free L-AAs, providing new preclinical piece of information which can shed a shadow on the mechanism of action of these products on PKU patients and their future management.

Health-related quality of life in a european sample of adults with early-treated classical PKU

BACKGROUND

Phenylketonuria (PKU) is a rare inborn error of metabolism affecting the catabolism of phenylalanine (Phe). To date, findings regarding health-related quality of life (HRQoL) in adults with early-treated classical PKU are discrepant. Moreover, little is known about metabolic, demographic, and cognitive factors associated with HRQoL. Hence, we aimed to investigate HRQoL and its association with demographic, metabolic, and cognitive characteristics in a large European sample of adults with early-treated classical PKU.

RESULTS

This cross-sectional study included 124 adults with early-treated classical PKU from Hungary, Italy, Spain, Switzerland, and Turkey. All participants prospectively completed the PKU quality of life questionnaire (PKU-QoL), a questionnaire specifically designed to evaluate the impact of PKU and its treatment on HRQoL in individuals with PKU. In addition, information about Phe levels (concurrent and past year), demographic (age and sex), and cognitive variables (intelligence quotient, IQ) were collected. Most domains revealed little or no impact of PKU on HRQoL and more than three-quarters of the patients rated their health status as good, very good, or excellent. Nevertheless, some areas of concern for patients were identified. Patients were worried about the guilt that they experience if they do not adhere to the dietary protein restriction and they were most concerned about high Phe levels during pregnancy. Further, tiredness was the most affected symptom, and the supplements' taste was considered a main issue for individuals with PKU. The overall impact of PKU on HRQoL was higher in women (U = 1315.5, p = .012) and in adults with a lower IQ (rs = - 0.448, p = .005). The overall impact of dietary protein restriction was higher in adults with higher concurrent Phe levels (rs = 0.272, p = .007) and higher Phe levels during the past year (rs = 0.280, p = .009).

CONCLUSION

The impact of PKU on most domains assessed in the PKU-QoL was considered to be low. These results likely reflect the successful implementation of the newborn screening resulting in the prevention of severe adverse long-term outcomes. However, a particular clinical focus should be given to patients with lower IQ, higher Phe levels, and women, as these variables were associated with a lower HRQoL.

Low bone mineralization in phenylketonuria may be due to undiagnosed metabolic acidosis

Background

Dietary intervention is to date the mainstay treatment to prevent toxic phenylalanine (Phe) accumulation in PKU patients. Despite success preventing central nervous system damage, there is increasing evidence of possible other unfavorable outcomes affecting other systems, e.g. kidney and bone; underlying mechanisms are yet to be fully elucidated.

Methods

This observational, cross-sectional and descriptive study investigated 20 adult with PKU evaluating biochemical parameters, BMD measurements and extrapolating data from 3-days food records and protein substitutes (PS) and special low protein foods (SLPF) composition.

Results

Blood gas venous analysis (VBG) indices were indicative of metabolic acidosis in 60% of PKU patients and VBG pH significantly correlated with BMD's Z-score (p-value = 0.022) even if its overall mean was in range (-1.29). Low bone mineral density for chronological age (Z-score < - 2.0) was found in 4 patients (20%). Indices of kidney function were not impaired. All used PS had a moderate excess of acidity, while SLPF were alkalizing and type/variety of consumed vegetables did not determine significant changes in acid-base equilibrium. Total intakes of potassium and magnesium were lower than expected.

Discussion

PKU patients seem to be at risk of metabolic acidosis, directly linked to possible low bone mineralization. This may be related to the acidic composition of PS, potentially capable of acidifying the entire diet. Reported low intakes of potassium and magnesium may be relevant to these observations. Further studies are needed to better address these topics.

A food pyramid for adult patients with phenylketonuria and a systematic review on the current evidences regarding the optimal dietary treatment of adult patients with PKU

Early dietary treatment is mind-saving in patients with phenylketonuria. A "diet-for-life" is advocated, aimed to prevent effects of chronic exposure to hyperphenylalaninemia. While adherence to diet is significant during childhood as patients are followed-up at specialized metabolic centers, during adolescence and adulthood percentage of patients discontinuing diet and/or lost at follow-up is still high. The process of passing skills and responsibilities from pediatric team to adult team is defined "transition". The goal of transition clinics is to set up specific multidisciplinary care pathways and guarantee continuity of care and compliance of patients to care. In 2017, "The complete European guidelines on phenylketonuria" were published. These guidelines, however, do not provide an easy way to illustrate to adult patients how to follow correct dietary approach. The purpose of this review is to evaluate current evidence on optimum dietary treatment of adults with phenylketonuria and to provide food pyramid for this population. The pyramid built shows that carbohydrates should be consumed every day (3 portions), together with fruits and vegetables (5 portions), extra virgin olive oil, and calcium water (almost 1 L/day); weekly portions can include 150 g potatoes walnuts and hazelnuts (20 g). At top of pyramid, there are two pennants. The green means that, based on individual metabolic phenotype and daily phenylalanine tolerance, patients need personalized supplementation (specific phenylalanine free amino acid mixtures, vitamins and omega 3 fatty acids); the one red indicates foods that are banned from diet (aspartame and protein foods exceeding individual dietary phenylalanine tolerance).

The BMI Z-Score and Protein Energy Ratio in Early- and Late-Diagnosed PKU Patients from a Single Reference Center in Mexico

The relationship between protein and energy and their appropriate proportions in hyperphenylalaninemia (HPA) or phenylketonuria (PKU) patients in terms of growth have been poorly studied, especially in those diagnosed late. We aimed to describe the protein energy ratio (P:E) and its association with body mass index (BMI) in 638 dietetic and anthropometric assessments from 54 early- or late-diagnosed HPA/PKU patients. Dietetic and anthropometric data were analyzed and classified according to BMI Z-Score and type of diagnosis, early by newborn screening (NBS) or late. Correlation between BMI Z-Score and P:E ratio was established. Percent of dietary protein from Phe-free metabolic formula was analyzed. According to the BMI Z-Score, the majority of assessments were eutrophic (69.4%). The median P:E ratio was >4 in most of the overweight assessments. Remarkably, the underweight group consumed the highest proportion of Phe-free metabolic formula (74.5%). A positive correlation between BMI Z-Score and P:E ratio was found. The highest proportion of underweight was found in the late-diagnosed patients. Our findings might be related to their nutritional history previous to the HPA/PKU treatment. Thus, complex nutritional outcome of the late-diagnosed HPA/PKU patients deserves actions to guarantee the early diagnosis, closer nutritional follow-up and alternative therapeutic approaches.

Phenylalanine free infant formula in the dietary management of phenylketonuria

BACKGROUND

Phenylalanine-free infant formula is an essential source of safe protein in a phenylalanine restricted diet, but its efficacy is rarely studied. We report a multicentre, open, longitudinal, prospective intervention study on a phenylalanine-free infant formula (PKU Start: Vitaflo International Ltd.).

RESULTS

This was a 2-part study: part I (28 days short term evaluation) and part II (12 months extension). Data was collected on infant blood phenylalanine concentrations, dietary intake, growth, and gastrointestinal tolerance. Ten infants (n = 8 males, 80%), with a median age of 14 weeks (range 4-36 weeks) were recruited from 3 treatment centres in the UK. Nine of ten infants completed the 28-day follow-up (one caregiver preferred the usual phenylalanine-free formula and discontinued the study formula after day 14) and 7/9 participated in study part II. The phenylalanine-free infant formula contributed a median of 57% (IQR 50-62%) energy and 53% (IQR 33-66%) of total protein intake from baseline to the end of the part II extension study. During the 12-month follow-up, infants maintained normal growth and satisfactory blood phenylalanine control. Any early gastrointestinal symptoms (constipation, colic, vomiting and poor feeding) improved with time.

CONCLUSION

The study formula was well tolerated, helped maintain good metabolic control, and normal growth in infants with PKU. The long-term efficacy of phenylalanine-free infant formula should continue to be observed and monitored.

Clinical, genetic, and experimental research of hyperphenylalaninemia

Hyperphenylalaninemia (HPA) is the most common amino acid metabolism defect in humans. It is an autosomal-recessive disorder of the phenylalanine (Phe) metabolism, in which high Phe concentrations and low tyrosine (Tyr) concentrations in the blood cause phenylketonuria (PKU), brain dysfunction, light pigmentation and musty odor. Newborn screening data of HPA have revealed that the prevalence varies worldwide, with an average of 1:10,000. Most cases of HPA result from phenylalanine hydroxylase (PAH) deficiency, while a small number of HPA are caused by defects in the tetrahydrobiopterin (BH4) metabolism and DnaJ heat shock protein family (Hsp40) member C12 (DNAJC12) deficiency. Currently, the molecular pathophysiology of the neuropathology associated with HPA remains incompletely understood. Dietary restriction of Phe has been highly successful, although outcomes are still suboptimal and patients find it difficult to adhere to the treatment. Pharmacological treatments, such as BH4 and phenylalanine ammonia lyase, are available. Gene therapy for HPA is still in development.

Transitioning of protein substitutes in patients with phenylketonuria: evaluation of current practice

Background

In children with phenylketonuria (PKU), transitioning protein substitutes at the appropriate developmental age is essential to help with their long-term acceptance and ease of administration. We assessed the parental experiences in transitioning from a second stage to third stage liquid or powdered protein substitute in patients with PKU.

Results

Sixteen interviews (23 open-ended questions) were carried out with parents/caregivers of children with PKU (8 females, 50%) with a median age of 8 years (range 5–11 years), continuously treated with diet, and on a third stage protein substitute. Parents/caregivers identified common facilitators and barriers during the third stage protein substitute transition process. The main facilitators were: child and parent motivation, parent knowledge of the transition process, a role model with PKU, low volume and easy preparation of the third stage protein substitute (liquid/powder), anticipation of increasing child independence, lower parent workload, attractive packaging, better taste and smell, school and teacher support, dietetic plans and guidance, PKU social events, child educational materials and written resources. The main barriers were child aversion to new protein substitutes, poor child behaviour, child aged > 5 years, parental fear of change, the necessity for  parental time and persistence, loss of parental control, high product volume, different taste, smell, and texture of new protein substitutes, and peer bullying.

Conclusion

A stepwise, supportive approach is necessary when transitioning from second to third stage protein substitutes in PKU. Future studies are needed to develop guidance to assist parents/caregivers, health professionals, and teachers during the transition process.

Present and future of lipid nanoparticle-mRNA technology in phenylketonuria disease treatment

Phenylketonuria (PKU) is a metabolic rare disease characterized by a failure of the body to clear out the high levels of Phenylalanine (Phe), leading to devastating neurological defects and growth retardation. PKU was discovered in 1934 by AsbjrØrn FØlling, and even though there have been continuous efforts from the scientific community to find therapeutic approaches to modulate the high levels of phenylalanine found in the body of the PKU patients, an efficient therapy still needs to be developed. Current standard of care includes low phenylalanine diets, but the strict restrictions for patients and families makes it very difficult to adequately being implemented. FDA has approved two drugs to help reduce Phe levels in PKU patients: an enzyme substitution therapy, Palynziq® (PEGylated recombinant phenylalanine ammonia lyase), and Kuvan®, a supplemental tetrahydrobiopterin (BH4) cofactor that enhances residual enzyme activity. Both treatments are restricted to certain PKU patients' population, and, therefore, there are still high unmet needs for most of the patients. The present review will focus on current advancements in lipid nanoparticles (LNP)-mRNA technologies and their potential in treating the root cause of PKU, a therapeutic approach that will be analyzed in the context of other promising therapeutic approaches that are been developed for PKU.

In Vivo Metabolic Responses to Different Formulations of Amino Acid Mixtures for the Treatment of Phenylketonuria (PKU)

Phenylketonuria (PKU) is a rare autosomal recessive inborn error of metabolism where the mainstay of treatment is a Phe restricted diet consisting of a combination of limited amounts of natural protein with supplementation of Phe-free or low-Phe protein substitutes and special low protein foods. Suboptimal outcomes may be related to the different absorption kinetics of free AAs, which have lower biological efficacy than natural proteins. Physiomimic Technology^TM is a technology engineered to prolong AA (AA-PT) release allowing physiological absorption and masking the odor and taste of free AAs. The aim of these studies was to assess the impact of AA-PT formulation on selected functional and metabolic parameters both in acute and long-term experimental studies. Adult rats in fasting conditions were randomized in different groups and treated by oral gavage. Acute AA-PT administration resulted in significantly lower BUN at 90 min versus baseline. Both BUN and glycemia were modulated in the same direction as intact casein protein. Long-term treatment with AA-PT significantly reduces the protein expression of the muscle degradation marker Bnip3L (−46%) while significantly increasing the proliferation of market myostatin (+58%). Animals dosed for 15 days with AA-PT had significantly stronger grip strength (+30%) versus baseline. In conclusion, the results suggest that the AA-PT formulation may have beneficial effects on both AA oxidation and catabolism with a direct impact on muscle as well as on other metabolic pathways.

Glycomacropeptide in PKU-Does It Live Up to Its Potential?

The use of casein glycomacropeptide (CGMP) as a protein substitute in phenylketonuria (PKU) has grown in popularity. CGMP is derived from κ casein and is a sialic-rich glycophosphopeptide, formed by the action of chymosin during the production of cheese. It comprises 20–25% of total protein in whey products and has key biomodulatory properties. In PKU, the amino acid sequence of CGMP has been adapted by adding the amino acids histidine, leucine, methionine, tyrosine and tryptophan naturally low in CGMP. The use of CGMP compared to mono amino acids (L-AAs) as a protein substitute in the treatment of PKU promises several potential clinical benefits, although any advantage is supported only by evidence from non-PKU conditions or PKU animal models. This review examines if there is sufficient evidence to support the bioactive properties of CGMP leading to physiological benefits when compared to L-AAs in PKU, with a focus on blood phenylalanine control and stability, body composition, growth, bone density, breath odour and palatability.

Effect of nutritional intervention on nutritional status among children with disorders of amino acid and nitrogen metabolism (AANMDs): A scoping review

Disorders of amino acid and nitrogen metabolism (AANMDs) occur due to an enzyme deficiency in a normal biochemical pathway. Nutritional intervention is recognized as the mainstay of treatment for children diagnosed with AANMD. Hence, this scoping review aimed to identify the nutritional interventions available in managing AANMD disorders and their effects on nutritional status. A systematic search using PRISMA Extension for Scoping Reviews (PRISMA-ScR) method was conducted across 4 databases: PubMed, ScienceDirect (Elsevier), EBSCOhost and Cochrane Central Register of Controlled Trials (CENTRAL). Inclusion criteria for the study to be selected are: subjects aged less than 18-year-old, article published in English, utilized an experimental design and published within the past 20 years. A total of 22 articles were included in this review. The majority of the subjects are boys (55.6%) and employed a randomized controlled trial (RCT) study design (45.4%). Nutritional interventions were categorized into 4 categories which are: "protein substitute" (n = 5), "protein substitute with modified composition" (n = 6), "nutrient supplementation (n=8)", and "distribution and dosage of protein substitute (n = 3)". The most frequently assessed outcomes were biochemical parameters that gauge the effectiveness of metabolic control (68.2%). Overall, "protein substitute enriched with inhibitive amino acids", "long-chain polyunsaturated fatty acids supplementation", and "evenly distributed protein substitute" demonstrated beneficial effects towards the nutritional status, especially in terms of biochemical parameters. In summary, nutritional intervention plays a significant role in improving the nutritional status of AANMD patients. Further investigations of nutritional intervention among AANMD children using a meta-analysis approach are necessary for better comprehension of their impact in management of AANMD disorders.

Is the Phenylalanine-Restricted Diet a Risk Factor for Overweight or Obesity in Patients with Phenylketonuria (PKU)? A Systematic Review and Meta-Analysis

Although there is a general assumption that a phenylalanine (Phe)-restricted diet promotes overweight in patients with phenylketonuria (PKU), it is unclear if this presumption is supported by scientific evidence. This systematic review aimed to determine if patients with PKU are at a higher risk of overweight compared to healthy individuals. A literature search was carried out on PubMed, Cochrane Library, and Embase databases. Risk of bias of individual studies was assessed using the Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies, and the quality of the evidence for each outcome was assessed using the NutriGrade scoring system. From 829 articles identified, 15 were included in the systematic review and 12 in the meta-analysis. Body mass index (BMI) was similar between patients with PKU and healthy controls, providing no evidence to support the idea that a Phe-restricted diet is a risk factor for the development of overweight. However, a subgroup of patients with classical PKU had a significantly higher BMI than healthy controls. Given the increasing prevalence of overweight in the general population, patients with PKU require lifelong follow-up, receiving personalised nutritional counselling, with methodical nutritional status monitoring from a multidisciplinary team in inherited metabolic disorders.

Phenylketonuria

Phenylketonuria (PKU; also known as phenylalanine hydroxylase (PAH) deficiency) is an autosomal recessive disorder of phenylalanine metabolism, in which especially high phenylalanine concentrations cause brain dysfunction. If untreated, this brain dysfunction results in severe intellectual disability, epilepsy and behavioural problems. The prevalence varies worldwide, with an average of about 1:10,000 newborns. Early diagnosis is based on newborn screening, and if treatment is started early and continued, intelligence is within normal limits with, on average, some suboptimal neurocognitive function. Dietary restriction of phenylalanine has been the mainstay of treatment for over 60 years and has been highly successful, although outcomes are still suboptimal and patients can find the treatment difficult to adhere to. Pharmacological treatments are available, such as tetrahydrobiopterin, which is effective in only a minority of patients (usually those with milder PKU), and pegylated phenylalanine ammonia lyase, which requires daily subcutaneous injections and causes adverse immune responses. Given the drawbacks of these approaches, other treatments are in development, such as mRNA and gene therapy. Even though PAH deficiency is the most common defect of amino acid metabolism in humans, brain dysfunction in individuals with PKU is still not well understood and further research is needed to facilitate development of pathophysiology-driven treatments.

The First Treatment for PKU: The Pioneers-Birmingham 1951

Prior to the introduction of newborn screening, Phenylketonuria (PKU) was a devastating disorder with affected individuals usually committed to a life in care in large institutions (asylums). Newborn screening only began after it was shown that those with PKU could be treated with a modified diet and could subsequently lead normal lives. The first production of a diet and the demonstration of its effectiveness was thus a key milestone in the history of both PKU and newborn screening, and took place in Birmingham, UK, in 1951. The pioneers were a two-year-old girl called Sheila Jones, her mother Mary, and three dedicated professionals at Birmingham Children's Hospital: Evelyn Hickmans, John Gerrard and Horst Bickel. Together, they changed the course of PKU for those across the world. This review summarises the history and achievements of this team who opened the door to PKU treatment and the introduction of newborn screening.