PTC923 (sepiapterin) lowers elevated blood phenylalanine in subjects with phenylketonuria: a phase 2 randomized, multi-center, three-period crossover, open-label, active controlled, all-comers study.

BACKGROUND & AIM: PTC923 (formerly CNSA-001), an oral formulation of sepiapterin, a natural precursor of intracellular tetrahydrobiopterin (BH4), has been shown in humans to induce larger increases in circulating BH4 vs. sapropterin dihydrochloride. Sapropterin reduces blood phenylalanine (Phe) by ≥20-30% in a minority of subjects with PKU. This was a Phase 2 randomized, multicenter, three-period crossover, open-label, active controlled, all-comers [regardless of phenylalanine hydroxylase (PAH) variants] comparison of PTC923 60 mg/kg, PTC923 20 mg/kg and sapropterin 20 mg/kg in 24 adults with phenylketonuria (PKU) and hyperphenylalaninemia. METHODS: Eligible subjects were adult men or women (18-60 y) with PKU. Subjects enrolled received 7 days of once-daily oral treatment with PTC923 20 mg/kg/day, PTC923 60 mg/kg/day and sapropterin dihydrochloride 20 mg/kg/day each in a random order. Treatments were separated by a 7-day washout. Subjects maintained their usual pre-study diet, including consumption of amino acid mixtures. Blood Phe was measured on Day 1 (predose baseline), Day 3, Day 5, and Day 7 of each treatment period. RESULTS: Least squares mean changes (SE) from baseline in blood Phe were: -206.4 (41.8) µmol/L for PTC923 60 mg/kg (p < 0.0001); -146.9 (41.8) µmol/L for PTC923 20 mg/kg (p = 0.0010); and - 91.5 (41.7) µmol/L for sapropterin (p = 0.0339). Effects of PTC923 60 mg/kg on blood Phe vs. sapropterin were significantly larger (p = 0.0098) and faster in onset with a significantly larger mean reduction in blood Phe at day 3 of treatment, p = 0.0135 (20 mg/kg) and p = 0.0007 (60 mg/kg). Only PTC923 60 mg/kg reduced blood Phe in classical PKU subjects (n = 11, p = 0.0287). The mean blood Phe reduction (PTC923 60 mg/kg) in a cofactor responder analysis (n = 8; baseline Phe ≥300 µmol/L and blood Phe reduction ≥30%) was -463.3 µmol/L (SE 51.5) from baseline. Adverse events were mostly mild to moderate, transient, and similar across treatment groups with no serious adverse events or discontinuations. CONCLUSIONS: The substantially significantly better effect of PTC923 60 mg/kg on blood Phe reduction vs. sapropterin supports further clinical development of PTC923 for PKU; ANZCTR number, ACTRN12618001031257.

Blood phenylalanine reduction reverses gene expression changes observed in a mouse model of phenylketonuria.

Phenylketonuria (PKU) is a genetic deficiency of phenylalanine hydroxylase (PAH) in liver resulting in blood phenylalanine (Phe) elevation and neurotoxicity. A pegylated phenylalanine ammonia lyase (PEG-PAL) metabolizing Phe into cinnamic acid was recently approved as treatment for PKU patients. A potentially one-time rAAV-based delivery of PAH gene into liver to convert Phe into tyrosine (Tyr), a normal way of Phe metabolism, has now also entered the clinic. To understand differences between these two Phe lowering strategies, we evaluated PAH and PAL expression in livers of PAHenu2 mice on brain and liver functions. Both lowered brain Phe and increased neurotransmitter levels and corrected animal behavior. However, PAL delivery required dose optimization, did not elevate brain Tyr levels and resulted in an immune response. The effect of hyperphenylalanemia on liver functions in PKU mice was assessed by transcriptome and proteomic analyses. We observed an elevation in Cyp4a10/14 proteins involved in lipid metabolism and upregulation of genes involved in cholesterol biosynthesis. Majority of the gene expression changes were corrected by PAH and PAL delivery though the role of these changes in PKU pathology is currently unclear. Taken together, here we show that blood Phe lowering strategy using PAH or PAL corrects both brain pathology as well as previously unknown lipid metabolism associated pathway changes in liver.

Beneficial Effects of Slow-Release Large Neutral Amino Acids after a Phenylalanine Oral Load in Patients with Phenylketonuria.

The mainstay of phenylketonuria treatment is a low protein diet, supplemented with phenylalanine (Phe)-free protein substitutes and micronutrients. Adhering to this diet is challenging, and even patients with good metabolic control who follow the dietary prescriptions in everyday life ignore the recommendations occasionally. The present study explores the ability of slow-release large neutral amino acids (srLNAAs) to prevent Phe increase following a Phe dietary load. Fourteen phenylketonuric patients aged ≥13 years were enrolled in a 6-week protocol. Oral acute Phe loads of 250 and 500 mg were added to the evening meal together with srLNAAs (0.5 gr/kg). Phe and tyrosine were dosed before dinner, 2h-after dinner, and after the overnight fast. After oral Phe loads, mean plasma Phe remained stable and below 600 µmol/L. No Phe peaks were registered. Tyrosine levels significantly increased, and Phe/Tyrosine ratio decreased. No adverse events were registered. In conclusion, a single oral administration of srLNAAs at the dose of 0.5 gr/kg is effective in maintaining stable plasma Phe during acute oral loads with Phe-containing food and may be added to the dietetic scheme in situations in which patients with generally good adherence to diet foresee a higher than prescribed Phe intake due to their commitments.

Correlations of blood and brain biochemistry in phenylketonuria: Results from the Pah-enu2 PKU mouse.

BACKGROUND: In phenylketonuria (PKU), treatment monitoring is based on frequent blood phenylalanine (Phe) measurements, as this is the predictor of neurocognitive and behavioural outcome by reflecting brain Phe concentrations and brain biochemical changes. Despite clinical studies describing the relevance of blood Phe to outcome in PKU patients, blood Phe does not explain the variance in neurocognitive and behavioural outcome completely. METHODS: In a PKU mouse model we investigated 1) the relationship between plasma Phe and brain biochemistry (Brain Phe and monoaminergic neurotransmitter concentrations), and 2) whether blood non-Phe Large Neutral Amino Acids (LNAA) would be of additional value to blood Phe concentrations to explain brain biochemistry. To this purpose, we assessed blood amino acid concentrations and brain Phe as well as monoaminergic neurotransmitter levels in in 114 Pah-Enu2 mice on both B6 and BTBR backgrounds using (multiple) linear regression analyses. RESULTS: Plasma Phe concentrations were strongly correlated to brain Phe concentrations, significantly negatively correlated to brain serotonin and norepinephrine concentrations and only weakly correlated to brain dopamine concentrations. From all blood markers, Phe showed the strongest correlation to brain biochemistry in PKU mice. Including non-Phe LNAA concentrations to the multiple regression model, in addition to plasma Phe, did not help explain brain biochemistry. CONCLUSION: This study showed that blood Phe is still the best amino acid predictor of brain biochemistry in PKU. Nevertheless, neurocognitive and behavioural outcome cannot fully be explained by blood or brain Phe concentrations, necessitating a search for other additional parameters. TAKE-HOME MESSAGE: Blood Phe is still the best amino acid predictor of brain biochemistry in PKU. Nevertheless, neurocognitive and behavioural outcome cannot fully be explained by blood or brain Phe concentrations, necessitating a search for other additional parameters.

Metabolic Control of Patients with Phenylketonuria in a Portuguese Metabolic Centre Comparing Three Different Recommendations.

Blood phenylalanine (Phe) is used as the primary marker to evaluate metabolic control. Our study aimed to describe the metabolic control of patients with phenylketonuria (PKU) comparing three different treatment recommendations (European guidelines/US guidelines/Portuguese consensus). This was a retrospective, observational, single centre study in patients with PKU collecting data on blood Phe levels from 2017. Nutritional intake data and sapropterin (BH4) prescription were collected at the last appointment of 2017. The final sample studied included 87 patients (48% females) [13 hyperphenylalaninemia; 47 mild PKU; 27 classical PKU] with a median age of 18 y (range: 1-36 y). The median number of blood Phe measurements for patients was 21 (range: 6-89). In patients aged < 12 y, the median blood Phe level was 300 µmol/L (range 168-480) and 474 µmol/L (range 156-1194) for patients ≥ 12 y. Overall, a median of 83% of blood Phe levels were within the European PKU guidelines target range. In patients aged ≥ 12 years, there was a higher median % of blood Phe levels within the European PKU guidelines target range (≥12 y: 84% vs. <12 y: 56%). In children < 12 y with classical PKU (n = 2), only 34% of blood Phe levels were within target range for all 3 guidelines and 49% with mild PKU (n = 11). Girls had better control than boys (89% vs. 66% median Phe levels within European Guidelines). Although it is clear that 50% or more patients were unable to achieve acceptable metabolic control on current treatment options, a globally agreed upper Phe target associated with optimal outcomes for age groups is necessary. More studies need to examine how clinics with dissimilar resources, different therapeutic Phe targets and frequency of monitoring relate to metabolic control.

Safety and pharmacodynamics of an engineered E. coli Nissle for the treatment of phenylketonuria: a first-in-human phase 1/2a study.

Phenylketonuria (PKU) is a rare disease caused by biallelic mutations in the PAH gene that result in an inability to convert phenylalanine (Phe) to tyrosine, elevated blood Phe levels and severe neurological complications if untreated. Most patients are unable to adhere to the protein-restricted diet, and thus do not achieve target blood Phe levels. We engineered a strain of E. coli Nissle 1917, designated SYNB1618, through insertion of the genes encoding phenylalanine ammonia lyase and L-amino acid deaminase into the genome, which allow for bacterial consumption of Phe within the gastrointestinal tract. SYNB1618 was studied in a phase 1/2a randomized, placebo-controlled, double-blind, multi-centre, in-patient study ( NCT03516487 ) in adult healthy volunteers (n = 56) and patients with PKU and blood Phe level ≥600 mmol l-1 (n = 14). Participants were randomized to receive a single dose of SYNB1618 or placebo (part 1) or up to three times per day for up to 7 days (part 2). The primary outcome of this study was safety and tolerability, and the secondary outcome was microbial kinetics. A D5-Phe tracer (15 mg kg-1) was used to study exploratory pharmacodynamic effects. SYNB1618 was safe and well tolerated with a maximum tolerated dose of 2 × 1011 colony-forming units. Adverse events were mostly gastrointestinal and of mild to moderate severity. All participants cleared the bacteria within 4 days of the last dose. Dose-responsive increases in strain-specific Phe metabolites in plasma (trans-cinnamic acid) and urine (hippuric acid) were observed, providing a proof of mechanism for the potential to use engineered bacteria in the treatment of rare metabolic disorders.

A Three-Year Longitudinal Study Comparing Bone Mass, Density, and Geometry Measured by DXA, pQCT, and Bone Turnover Markers in Children with PKU Taking L-Amino Acid or Glycomacropeptide Protein Substitutes.

In patients with phenylketonuria (PKU), treated by diet therapy only, evidence suggests that areal bone mineral density (BMDa) is within the normal clinical reference range but is below the population norm. AIMS: To study longitudinal bone density, mass, and geometry over 36 months in children with PKU taking either amino acid (L-AA) or casein glycomacropeptide substitutes (CGMP-AA) as their main protein source. METHODOLOGY: A total of 48 subjects completed the study, 19 subjects in the L-AA group (median age 11.1, range 5-16 years) and 29 subjects in the CGMP-AA group (median age 8.3, range 5-16 years). The CGMP-AA was further divided into two groups, CGMP100 (median age 9.2, range 5-16 years) (n = 13), children taking CGMP-AA only and CGMP50 (median age 7.3, range 5-15 years) (n = 16), children taking a combination of CGMP-AA and L-AA. Dual X-ray absorptiometry (DXA) was measured at enrolment and 36 months, peripheral quantitative computer tomography (pQCT) at 36 months only, and serum blood and urine bone turnover markers (BTM) and blood bone biochemistry at enrolment, 6, 12, and 36 months. RESULTS: No statistically significant differences were found between the three groups for DXA outcome parameters, i.e., BMDa (L2-L4 BMDa g/cm2), bone mineral apparent density (L2-L4 BMAD g/cm3) and total body less head BMDa (TBLH g/cm2). All blood biochemistry markers were within the reference ranges, and BTM showed active bone turnover with a trend for BTM to decrease with increasing age. CONCLUSIONS: Bone density was clinically normal, although the median z scores were below the population mean. BTM showed active bone turnover and blood biochemistry was within the reference ranges. There appeared to be no advantage to bone density, mass, or geometry from taking a macropeptide-based protein substitute as compared with L-AAs.

The Impact of the First 2020 COVID-19 Lockdown on the Metabolic Control of Patients with Phenylketonuria.

The present study assessed patients' metabolic control of phenylketonuria (PKU) during the first 2020 COVID-19 lockdown in Poland. Blood (phenylalanine) Phe results of the tests of 535 patients, performed in 2019 and in the first months of 2020, were analysed. The six-week lockdown period was compared to the preceding six-week period as well as to the two corresponding periods of 2019 (three non-lockdown periods). More patients failed to perform Phe tests in the lockdown period (32.7%) than in non-lockdown periods (15.6%, 15.1%, 17.2%; p < 0.001 for all). The median Phe levels for those patients who performed testing in all the four periods did not differ between periods. However, these patients tended to perform only one test during the lockdown (ORs: 1.43 to 1.60; 95% CI: from 1.01-2.04 to 1.11-2.30, p-value 0.02 to 0.005). Patients who did not take blood during the lockdown (46.7%) performed significantly fewer blood tests in the remaining periods (median : 1 <0-1> vs. 2 <1-4>; p < 0.001). In conclusion, direct assessment of patients' compliance based upon Phe levels during the pandemic lockdown was not possible. Pre-pandemic non-compliant patients frequently failed to perform the test during the lockdown, whereas the previously compliant ones were more likely to perform only one test. This strongly suggests that metabolic control might have worsened.

Long-term cognitive and psychosocial outcomes in adults with phenylketonuria.

Previous studies have suggested that cognitive and psychosocial underfunctioning in early-treated adults with phenylketonuria (PKU) may be explained by suboptimal adherence to dietary treatments, however, these studies often employ small samples, with different outcome measures, definitions and cut-offs. Samples have also tended to comprise participants with a limited range of blood phenylalanine concentrations, and often individuals who may not have been treated early enough to avoid neurological damage. In this study, we explore the impact of lifetime dietary control, as indicated by blood phenylalanine concentrations in childhood, adolescence and adulthood, on long-term cognitive and psychosocial outcomes in a large sample of adults with PKU who were diagnosed by neonatal screening and commenced on dietary treatment within the first month of life. One hundred and fifty-four participants underwent cognitive testing, assessing attention, learning, working memory, language, executive functioning and processing speed. One hundred and forty-nine completed measures of psychosocial functioning, documenting educational, occupational, quality of life, emotional and social outcomes which were compared with a group of healthy controls. Many adults with PKU demonstrated cognitive impairments, most frequently affecting processing speed (23%), executive function (20%) and learning (12%). Cognitive outcomes were related to measures of historic metabolic control, but only processing speed was significantly related to phenylalanine concentration at the time of testing after controlling for historic levels. Adults with PKU did not, however, differ from controls in educational, occupational, quality of life or emotional outcomes, or on a measure of family functioning, and showed only minor differences in relationship style. These findings have implications for patient counselling and decisions regarding the management of PKU in adulthood.

Pharmacokinetic, pharmacodynamic, and immunogenic rationale for optimal dosing of pegvaliase, a PEGylated bacterial enzyme, in adult patients with phenylketonuria.

Phenylketonuria (PKU), a deficiency in the activity of the enzyme phenylalanine hydroxylase, leads to toxic levels of phenylalanine (Phe) in the blood and brain. Pegvaliase (recombinant Anabaena variabilis phenylalanine ammonia lyase conjugated with polyethylene glycol) is approved to manage PKU in patients aged greater than or equal to 18 years in the United States and in patients aged greater than or equal to 16 years in the European Union. Pharmacokinetic, pharmacodynamic, and immunogenicity results from five open-label pegvaliase trials were assessed. Studies with induction/titration/maintenance (I/T/M) dosing regimens demonstrated pharmacokinetic stabilization and sustained efficacy associated with maintenance doses (20, 40, or 60 mg/day). Immune-mediated pegvaliase clearance was high during induction/titration phases when the early immune response was peaking. The combination of low drug dosage and high drug clearance led to low drug exposure and minimal decreases in blood Phe levels during induction/titration. Higher drug exposure and substantial reductions in blood Phe levels were observed later in treatment as drug clearance was reduced due to the maturation of the immune response, which allowed for increased dosing to target levels. The incidence of hypersensitivity reactions was temporally associated with the peaking of the early antidrug immune response and decreased with time as immune response matured after the first 6 months of treatment. These results support an I/T/M dosing regimen and suggest a strategy for administration of other nonhuman biologics to achieve efficacy and improve tolerability.

Growth and Body Composition in PKU Children-A Three-Year Prospective Study Comparing the Effects of L-Amino Acid to Glycomacropeptide Protein Substitutes.

Protein quality and quantity are important factors in determining lean body (muscle) mass (LBM). In phenylketonuria (PKU), protein substitutes provide most of the nitrogen, either as amino acids (AA) or glycomacropeptide with supplementary amino acids (CGMP-AA). Body composition and growth are important indicators of long-term health. In a 3-year prospective study comparing the impact of AA and CGMP-AA on body composition and growth in PKU, 48 children were recruited. N = 19 (median age 11.1 years, range 5-15 years) took AA only, n = 16 (median age 7.3 years, range 5-15 years) took a combination of CGMP-AA and AA, (CGMP50) and 13 children (median age 9.2 years, range 5-16 years) took CGMP-AA only (CGMP100). A dual energy X-ray absorptiometry (DXA) scan at enrolment and 36 months measured LBM, % body fat (%BF) and fat mass (FM). Height was measured at enrolment, 12, 24 and 36 months. No correlation or statistically significant differences (after adjusting for age, gender, puberty and phenylalanine blood concentrations) were found between the three groups for LBM, %BF, FM and height. The change in height z scores, (AA 0, CGMP50 +0.4 and CGMP100 +0.7) showed a trend that children in the CGMP100 group were taller, had improved LBM with decreased FM and % BF but this was not statistically significant. There appeared to be no advantage of CGMP-AA compared to AA on body composition after 3-years of follow-up. Although statistically significant differences were not reached, a trend towards improved body composition was observed with CGMP-AA when it provided the entire protein substitute requirement.

Implementing a Transition Program from Paediatric to Adult Services in Phenylketonuria: Results After Two Years of Follow-Up with an Adult Team.

We aimed to report the implementation of a phenylketonuria (PKU) transition program and study the effects of follow-up with an adult team on metabolic control, adherence, and loss of follow-up. Fifty-five PKU patients were analysed in the study periods (SP): 2 years before (SP1) and after the beginning of adult care (SP2). Retrospective data on metabolic control and number of clinic appointments were collected for each SP, and protein intakes were analysed. In SP2, three patients (6%) were lost to follow-up. There was a small but statistically significant increase in median number of annual blood spots from SP1 to SP2: 11 (7-15) vs. 14 (7-20); p = 0.002. Mean ± SD of median blood Phe remained stable (525 ± 248 µmol/L vs. 552 ± 225 µmol/L; p = 0.100); median % of blood Phe < 480 µmol/L decreased (51 (4-96)% vs. 37 (5-85)%; p = 0.041) and median number of clinic appointments increased from SP1 to SP2: (5 (4-6) vs. 11 (8-13); p < 0.001). No significant differences were found regarding any parameter of protein intake. Our results suggest that the implementation of an adult service was successful as impact on metabolic control was limited and attendance remained high. Continuous dietetic care likely contributed to these results by keeping patients in follow-up and committed to treatment.

Factors that increase risk for poor adherence to phenylketonuria treatment in Brazilian patients.

Neurotoxic effects caused by high phenylalanine (Phe) in patients with phenylketonuria (PKU) can be avoided through dietary treatment. However, achieving the recommended Phe levels has been a challenge. This study aimed to investigate factors associated with adherence to PKU treatment among patients followed at a medical genetics public service in southern Brazil. Twenty-nine patients (early diagnosed, n = 20; late-diagnosed, n = 9) with classical (n = 16) or mild PKU (n = 13) aged 6-34 years (16.4 ± 7.5) and 16 caregivers were included. Blood Phe levels were recorded, and assessment tools measuring barriers to treatment, IQ, knowledge about disease, treatment, and perceived adherence were collected. Classical PKU patients showed higher current blood Phe levels than mild PKU patients (U = 37.000, p = 0.003). Lifetime and childhood Phe levels were associated with recent metabolic control (τ = 0.76, p = 0.000; τ = 0.70, p = 0.000, respectively). The perception of barriers to treatment was associated with a higher blood Phe level (τ = 0.39, p = 0.003). Tolerance to Phe, metabolic control throughout childhood, and perceived difficulty in living with demands of treatment are important factors of greater vulnerability to poor adherence in PKU patients.

Defining tetrahydrobiopterin responsiveness in phenylketonuria: Survey results from 38 countries.

BACKGROUND: A subset of patients with phenylketonuria benefit from treatment with tetrahydrobiopterin (BH4), although there is no consensus on the definition of BH4 responsiveness. The aim of this study therefore was to gain insight into the definitions of long-term BH4 responsiveness being used around the world. METHODS: We performed a web-based survey targeting healthcare professionals involved in the treatment of PKU patients. Data were analysed according to geographical region (Europe, USA/Canada, other). RESULTS: We analysed 166 responses. Long-term BH4 responsiveness was commonly defined using natural protein tolerance (95.6%), improvement of metabolic control (73.5%) and increase in quality of life (48.2%). When a specific value for a reduction in phenylalanine concentrations was reported (n = 89), 30% and 20% were most frequently used as cut-off values (76% and 19% of respondents, respectively). When a specific relative increase in natural protein tolerance was used to define long-term BH4 responsiveness (n = 71), respondents most commonly reported cut-off values of 30% and 100% (28% of respondents in both cases). Respondents from USA/Canada (n = 50) generally used less strict cut-off values compared to Europe (n = 96). Furthermore, respondents working within the same center answered differently. CONCLUSION: The results of this study suggest a very heterogeneous situation on the topic of defining long-term BH4 responsiveness, not only at a worldwide level but also within centers. Developing a strong evidence- and consensus-based definition would improve the quality of BH4 treatment.

Protein Substitutes in PKU; Their Historical Evolution.

Protein substitutes developed for phenylketonuria (PKU) are a synthetic source of protein commonly based on L-amino acids. They are essential in the treatment of phenylketonuria (PKU) and other amino acid disorders, allowing the antagonistic amino acid to be removed but with the safe provision of all other amino acids necessary for maintaining normal physiological function. They were first formulated by a chemist and used experimentally on a 2-year-old girl with PKU and their nutritional formulations and design have improved over time. Since 2008, a bioactive macropeptide has been used as a base for protein substitutes in PKU, with potential benefits of improved bone and gut health, nitrogen retention, and blood phenylalanine control. In 2018, animal studies showed that physiomimic technology coating the amino acids with a polymer allows a slow release of amino acids with an improved physiological profile. History has shown that in PKU, the protein substitute's efficacy is determined by its nutritional profile, amino acid composition, dose, timing, distribution, and an adequate energy intake. Protein substitutes are often given little importance, yet their pharmacological actions and clinical benefit are pivotal when managing PKU.

Tyrosine supplementation for phenylketonuria.

BACKGROUND: Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap. However, the diet is very restrictive and unpalatable and can be difficult to follow. A deficiency of the amino acid tyrosine has been suggested as a cause of some of the neuropsychological problems exhibited in phenylketonuria. Therefore, this review aims to assess the efficacy of tyrosine supplementation for phenylketonuria. This is an update of previously published versions of this review. OBJECTIVES: To assess the effects of tyrosine supplementation alongside or instead of a phenylalanine-restricted diet for people with phenylketonuria, who commenced on diet at diagnosis and either continued on the diet or relaxed the diet later in life. To assess the evidence that tyrosine supplementation alongside, or instead of a phenylalanine-restricted diet improves intelligence, neuropsychological performance, growth and nutritional status, mortality rate and quality of life. SEARCH METHODS: We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register which is comprised of references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings. Additional studies were identified from handsearches of the Journal of Inherited Metabolic Disease (from inception in 1978 to 1998). The manufacturers of prescribable dietary products used in the treatment of phenylketonuria were also contacted for further references. Date of the most recent search of the Group's Inborn Errors of Metabolism Trials Register: 07 December 2020. SELECTION CRITERIA: All randomised or quasi-randomised trials investigating the use of tyrosine supplementation versus placebo in people with phenylketonuria in addition to, or instead of, a phenylalanine-restricted diet. People treated for maternal phenylketonuria were excluded. DATA COLLECTION AND ANALYSIS: Two authors independently assessed the trial eligibility, methodological quality and extracted the data. MAIN RESULTS: Six trials were found, of which three trials reporting the results of a total of 56 participants, were suitable for inclusion in the review. The blood tyrosine concentrations were significantly higher in the participants receiving tyrosine supplements than those in the placebo group, mean difference 23.46 (95% confidence interval 12.87 to 34.05). No significant differences were found between any of the other outcomes measured. The trials were assessed as having a low to moderate risk of bias across several domains. AUTHORS' CONCLUSIONS: From the available evidence no recommendations can be made about whether tyrosine supplementation should be introduced into routine clinical practice. Further randomised controlled studies are required to provide more evidence. However, given this is not an active area of research, we have no plans to update this review in the future.

Long-term preservation of intellectual functioning in sapropterin-treated infants and young children with phenylketonuria: A seven-year analysis.

Sapropterin dihydrochloride has been approved for the treatment of hyperphenylalaninemia in infants and young children with phenylketonuria (PKU). Sapropterin can reduce phenylalanine (Phe) levels in tetrahydrobiopterin (BH4)-responsive patients, potentially preventing the intellectual impairment caused by elevated Phe levels. The long-term effect of sapropterin on intellectual functioning was assessed using the Full-Scale Intelligence Quotient (FSIQ) in 62 children who began treatment before the age of 6 years. Over each 2-year interval, the estimate of mean change in FSIQ was -0.5768 with a lower limit of the 95% confidence interval (CI) of -1.60. At the end of the follow-up period (Year 7), the least squares mean estimate of the change in FSIQ from baseline was 1.14 with a lower limit of the 95% CI of -3.53. These lower limits were both within the clinically expected variation of 5 points. During the whole study period, mean blood Phe levels remained within the American College of Medical Genetics (ACMG) target range of 120-360 µmol/L. In addition, height, weight, and head circumference were maintained within normal ranges throughout follow-up, as defined by growth charts from the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) for children below and above the age of 24 months, respectively. All patients (n = 65) enrolled in this study experienced at least one adverse event, as expected from previous studies. In conclusion, long-term use of sapropterin in individuals with PKU helps to control blood Phe, preserve intellectual functioning, and maintain normal growth in BH4-responsive children who initiated treatment between the ages of 0 to 6 years.

Phenylalanine Effects on Brain Function in Adult Phenylketonuria.

OBJECTIVE: To evaluate the relationship between circulating phenylalanine and brain function as well as neuropsychiatric symptoms in adults with phenylketonuria. METHODS: In this prospective cross-sectional study, early-treated patients with phenylketonuria older than 30 years and age- and sex-matched controls were included. Extensive neurologic evaluation, neuropsychological and behavioral testing, sensory and motor evoked potentials, and MRI were performed. CSF concentrations of neurodegenerative markers were evaluated in addition in a subset of 10 patients. RESULTS: Nineteen patients with phenylketonuria (median age 41 years) with different phenylalanine levels (median 873 µmol/L) entered the study. They showed higher prevalence of neurologic symptoms, cognitive and behavioral abnormalities, autonomic dysfunction, alterations in neurophysiologic measures, and atrophy in putamen and right thalamus compared to controls. In CSF, patients with phenylketonuria exhibited higher ß-amyloid 1-42 (p = 0.003), total tau (p < 0.001), and phosphorylated tau (p = 0.032) levels compared to controls. Plasma phenylalanine levels highly correlated with the number of failed neuropsychological tests (r = 0.64, p = 0.003), neuropsychiatric symptoms (r = 0.73, p < 001), motor evoked potential latency (r = 0.48, p = 0.030), and parietal lobe atrophy. CONCLUSIONS: Our study provides strong evidence for a correlation between phenylalanine levels and clinical, neuropsychological, neurophysiologic, biochemical, and imaging alterations in adult patients with phenylketonuria.

Repeat-dose animal toxicity studies and genotoxicity study with deactivated alkaline serine protease (DASP), a protein low in phenylalanine (PHE).

Phenylketonuria (PKU) is an autosomal recessive inherited disorder affecting one in every 10,000 to 15,000 newborn children in the US each year. PKU patients' metabolism of an essential amino acid, phenylalanine (PHE), is impaired, resulting in concentrations of PHE in the circulating blood and brain that are potentially toxic. Individuals with PKU restrict dietary intakes of PHE by consuming medical foods formulated with low PHE concentrations. In this study, an alkaline serine protease (ASP) expressed in Bacillus licheniformis strain 2709, which is composed of >90% protein with a concentration of <0.25% PHE, was heat deactivated (becoming deactivated ASP (DASP)) and evaluated for safe use as an ingredient in foods, including medical foods. DASP was non-mutagenic with and without metabolic activation up to 5000 µg DASP/plate. 14-Day dietary studies supported a Maximum Tolerated Dose (MTD) of 115000 ppm DASP. In a 90-day dietary toxicity study, CRL SD CD® rats were administered 0, 28750, 57500, 115500 ppm DASP in the diet. No DASP-related adverse effects were observed at the high dose. As such, a No Observable Adverse Effect Level (NOAEL) of 115,500 ppm DASP or 6224.1 mg DASP/kg bw/day (males) and 7500.9 mg DASP/kg bw/day (females) was established.

Variants of the phenylalanine hydroxylase gene in neonates with phenylketonuria in Hainan, China.

OBJECTIVE: To investigate the incidence of phenylalanine hydroxylase (PAH) deficiency and PAH genotypes in neonates in Hainan, China. Methods: We performed heal stick to collect blood and obtain dry blood spot specimens from newborns in Hainan from January 2007 to December 2016. Phenylalanine (Phe) concentration in these dry blood spots was measured by the fluorescence method to screen phenylketonuria (PKU). For suspicious samples, the genotypes of the PAH gene were amplified by biotin labeled oligonucleotide primers. Polymerase chain reaction (PCR) products were then analyzed by flow-through hybridization to detect genotypes. At the same time, peripheral blood samples of children suspicious of PKU and their parents were used to perform gene sequencing. Results: Of the 914,520 newborns screened, 29 of them had PAH deficiency. The incidence of PAH deficiency in Hainan was 3.17/100,000. A total of 58 mutant alleles belonging to 15 different types were identified in the 29 patients. In terms of genotypes frequency, the top 4 were: c.611A > G 20.7% (12/58) , c.728G > A 17.2%, c.158G > A 15.2% (9/58) and c.721C > T 13.8% (8/58). The frequencies of other genotypes were all below 10%. Conclusion: The incidence of PAH deficiency in Hainan is relatively high among all provinces in southern China. With a total frequency of 67.2%, c.611A > G, c.728G > A, c.158G > A and c.721C > T, and are the most common PAH gene genotypes.