Blood Phe Concentrations Research Articles

Efficacy and safety of sapropterin dihydrochloride in patients with phenylketonuria: A meta-analysis of randomized controlled trials.

AimsThe aim of the present meta‐analysis was to evaluate the efficacy and safety of sapropterin dihydrochloride in phenylketonuria (PKU) patients.MethodsThe following databases were searched for randomized controlled trials (RCT) regarding PKU patients treated with sapropterin dihydrochloride: PubMed, Embase, Cochrane Library and clinicaltrials. Two authors independently selected studies, assessed the risk of bias and extracted data. The meta‐analysis was performed in RevMan 5.3 provided by the Cochrane Collaboration.ResultsFour studies met the inclusion criteria. In PKU patients with low blood phenylalanine (Phe) concentration, no significant difference was indicated for the decrease of Phe level (weighted mean difference (WMD) = −7.75 μmol L−1; 95% confidence intervals (CI): −82.63 to 67.13, P = 0.84, I 2 = 0%), however, the dietary Phe tolerance was significantly improved in the sapropterin group (WMD = 19.89 mg kg−1 d−1; 95% CI: 10.26 to 29.52, P < 0.0001, I 2 = 0%). In PKU patients with high blood Phe level, sapropterin showed a significant lowering in blood Phe concentration (WMD = −225.31 μmol L−1; 95% CI: −312.28 to −138.34, P < 0.00001, I 2 = 0%). There was no significant difference for adverse events.ConclusionsSapropterin could bring benefit for PKU patients with high or low Phe level, due to Phe reduction in a short time or dietary Phe tolerance improvement respectively. Sapropterin has an acceptable safety profile.

The Effect of Glycomacropeptide versus Amino Acids on Phenylalanine and Tyrosine Variability over 24 Hours in Children with PKU: A Randomized Controlled Trial.

Introduction: In phenylketonuria (PKU), evidence suggests that casein glycomacropeptide supplemented with rate-limiting amino acids (CGMP-AA) is associated with better protein utilisation and less blood phenylalanine (Phe) variability. Aim: To study the impact of CGMP-AA on blood Phe variability using 3 different dietary regimens in children with PKU. Methods: This was a 6-week randomised controlled cross-over study comparing CGMP-AA vs. Phe-free l-amino acids (l-AA) assessing blood Phe and tyrosine (Tyr) variability over 24 h in 19 children (7 boys) with PKU, with a median age of 10 years (6–16). Subjects were randomised to 3 dietary regimens: (1) R1, CGMP-AA and usual dietary Phe (CGMP + Phe); (2) R2, CGMP-AA − Phe content of CGMP-AA from usual diet (CGMP − Phe); and (3) R3, l-AA and usual dietary Phe. Each regimen was administered for 14 days. Over the last 48 h on days 13 and 14, blood spots were collected every 4 h at 08 h, 12 h, 16 h, 20 h, 24 h, and 04 h. Isocaloric intake and the same meal plan and protein substitute dosage at standardised times were maintained when blood spots were collected. Results: Eighteen children completed the study. Median Phe concentrations over 24 h for each group were (range) R1, 290 (30–580), R2, 220 (10–670), R3, 165 (10–640) μmol/L. R1 vs. R2 and R1 vs. R3 p < 0.0001; R2 vs. R3 p = 0.0009. There was a significant difference in median Phe at each time point between R1 vs. R2, p = 0.0027 and R1 vs. R3, p < 0.0001, but not between any time points for R2 vs. R3. Tyr was significantly higher in both R1 and R2 [70 (20–240 μmol/L] compared to R3 [60 (10–200) μmol/L]. In children < 12 years, blood Phe remained in the target range (120–360 μmol/L), over 24 h, for 75% of the time in R1, 72% in R2 and 64% in R3; for children aged ≥ 12 years, blood Phe was in target range (120–600 μmol/L) in R1 and R2 for 100% of the time, but 64% in R3. Conclusions: The residual Phe in CGMP-AA increased blood Phe concentration in children. CGMP-AA appears to give less blood Phe variability compared to l-AA, but this effect may be masked by the increased blood Phe concentrations associated with its Phe contribution. Reducing dietary Phe intake to compensate for CGMP-AA Phe content may help.

Development of a synthetic live bacterial therapeutic for the human metabolic disease phenylketonuria.

Phenylketonuria (PKU) is a genetic disease that is characterized by an inability to metabolize phenylalanine (Phe), which can result in neurotoxicity. To provide a potential alternative to a protein-restricted diet, we engineered Escherichia coli Nissle to express genes encoding Phe-metabolizing enzymes in response to anoxic conditions in the mammalian gut. Administration of our synthetic strain, SYNB1618, to the Pahenu2/enu2 PKU mouse model reduced blood Phe concentration by 38% compared with the control, independent of dietary protein intake. In healthy Cynomolgus monkeys, we found that SYNB1618 inhibited increases in serum Phe after an oral Phe dietary challenge. In mice and primates, Phe was converted to trans-cinnamate by SYNB1618, quantitatively metabolized by the host to hippurate and excreted in the urine, acting as a predictive biomarker for strain activity. SYNB1618 was detectable in murine or primate feces after a single oral dose, permitting the evaluation of pharmacodynamic properties. Our results define a strategy for translation of live bacterial therapeutics to treat metabolic disorders.

Comparison of different methods for measuring the phenylalanine concentration of phenylketonuria patients in dried blood spots

Objective To compare the phenylalanine(Phe) concentration in the sample of dried blood spot, measured by four different methods: fluorescence assay, tandem mass spectrometry (MS/MS), including MS/MS Derivatized, MS/MS Non-Derivatized and MS/MS-Standard Curve. Methods A total of 204 dried blood spot (DBS) samples of phenylketonuria (PKU) patients from Shanghai Xinhua Hospital were collected in this study. Phe concentration in DBS was measured by fluorescence assay and MS/MS assay, including MS/MS Derivatized, MS/MS Non-Derivatized and MS/MS-Standard Curve. The samples were divided into low, middle and high concentration groups according to Phe concentration, which were under the 360 μmol/L, between 360 and 600 μmol/L, and over 600 μmol/L respectively. The differences among the groups were analyzed by consistency check and non-parametric test. Results The within-day and between-day precisions of MS/MS-Standard Curve assay were 4.0%-7.2%, the recoveries were 93.2%-97.3%. Consistency check showed that less than 8.1% of Phe value were out of the 95% limit of agreement among these four methods. In the low and middle concentration groups, the quartile of Phe value measured by fluorescence assay, MS/MS Standard Curve and MS/MS Derivatized were 176 (118, 251)μmol/L, 174 (94, 273)μmol/L, 153 (94, 242)μmol/L; and 540 (478, 578)μmol/L, 485 (414, 529)μmol/L, 466 (402, 513)μmol/L, respectively. Phe value measured by fluorescence assay was significantly higher than that by MS/MS Standard Curve, the difference was 4.8%-9.0%, (Z=-3.787 to -2.674, P<0.01). Phe value obtained from MS/MS Non-Derivatized was less than that by MS/MS-Standard Curve, the difference was 3.9%-5.2%, (Z=-7.474 to -5.747, P<0.01). In the high concentration group, the quartile of Phe value measured by MS/MS-Standard Curve, MS/MS Derivatized, MS/MS Non-Derivatized and fluorescence assay were 807 (695, 924)μmol/L, 700 (575, 785)μmol/L, 680 (623, 771)μmol/L and 711 (674, 794)μmol/L, respectively. Phe value obtained from MS/MS Standard Curve was significantly higher than those from the other methods and the difference was 10.9%-16.2%, (Z=-4.458 to -4.356, P<0.01). Conclusions The MS/MS Standard Curve assay showed good specificity and accuracy. These four assays displayed good agreement. Although there was difference in measuring the Phe concentration among these methods, they could be used in blood Phe concentration monitoring for PKU patients.(Chin J Lab Med, 2018, 41: 361-365) Key words: Phenylketonurias; Phenylalanine; Dried blood spot testing; Tandem mass spectrometry

Pegvaliase for the treatment of phenylketonuria: A pivotal, double-blind randomized discontinuation Phase 3 clinical trial

IntroductionPegvaliase is a recombinant Anabaena variabilis phenylalanine ammonia lyase (PAL) enzyme under investigation for treatment of adult phenylketonuria (PKU). This manuscript describes results of a randomized discontinuation trial (RDT) designed to evaluate the effects of pegvaliase treatment on blood phenylalanine (Phe) and neuropsychiatric outcomes in adults with PKU. MethodsPRISM-2 is a 4-part, Phase 3 study that enrolled adults with PKU receiving pegvaliase treatment (initiated in a prior Phase 2 or Phase 3 study). The RDT, Part 2 of PRISM-2, was an 8-week trial that evaluated change in blood Phe concentrations, neuropsychiatric and neurocognitive measures, and safety outcomes in PRISM-2 participants who had achieved at least a 20% blood Phe reduction from pre-treatment baseline with pegvaliase treatment. Participants were randomized 2:1 to either continue pegvaliase (20 mg/day or 40 mg/day) or switch to matching placebo. ResultsThe pooled pegvaliase group enrolled 66 participants and each placebo group enrolled 14 participants. The primary endpoint of change in blood Phe concentration from RDT entry to RDT Week 8 was met with clinically meaningful and statistically significant differences between the pegvaliase and placebo groups. Mean (SD) blood Phe at the beginning of the RDT when all participants were receiving pegvaliase was 563.9 μM (504.6) in the group assigned to the 20 mg/day placebo group (n = 14), 508.2 μM (363.7) in those assigned to the 40 mg/day placebo group (n = 14), and 503.9 μM (520.3) in those assigned to continue pegvaliase treatment (n = 58). At Week 8 of the RDT, the least squares mean change (95% confidence interval) in blood Phe was 949.8 μM (760.4 to 1139.1) for the 20 mg/day placebo group and 664.8 μM (465.5 to 864.1) for the 40 mg/day placebo group in comparison to 26.5 μM (−68.3 to 121.3) for the pooled (20 mg/day and 40 mg/day) pegvaliase group (P < 0.0001 for pooled pegvaliase group vs each placebo group). Adverse events (AEs) were usually lower in the pooled placebo group when compared to the pooled pegvaliase group. The most common AEs for the pooled pegvaliase and pooled placebo groups were arthralgia (13.6% and 10.3%, respectively), headache (12.1% and 24.1%), anxiety (10.6% and 6.9%), fatigue (10.6% and 10.3%), and upper respiratory tract infection (1.5% and 17.2%). ConclusionMean blood Phe reduction was sustained in the pegvaliase group, while placebo groups had mean blood Phe concentration increase toward pre-treatment baseline levels. Results from this study confirmed the efficacy of pegvaliase in maintaining reduced blood Phe concentrations with a manageable safety profile for most participants.

First-year metabolic control guidelines and their impact on future metabolic control and neurocognitive functioning in children with PKU

There is a consensus on the importance of early and life-long treatment for PKU patients. Still, differences exist on target blood phenylalanine (Phe) concentrations for children with PKU in different countries and treatment centers. For the first time, long-term metabolic control and child development and cognitive functioning is compared between children with mean phenylalanine concentrations under 240μmol/L (group A), between 240 and 360μmol/L (group B) or over 360μmol/L (group C) during their first year of life. METHODS: 70 patients diagnosed with PKU through neonatal screening with Phe >900μmol/L, were divided into 3 groups: A, B and C, according to mean Phe concentrations and standard deviation (SD). Metabolic control during childhood, psychomotor development and IQ were compared. RESULTS: In group A, Phe was maintained within the recommended range until 6years of age, in Group B, until 3years of age, and in group C, Phe was always over the recommended range. No significant differences were found between the three groups in mental development index (MDI) and motor development index (PDI) scores at 12, 24, and 30months of age, but group C had the lowest scores on MDI at all age periods. At preschool and school age, IQ was higher in group A compared to group C. CONCLUSION: Results show that mean blood Phe concentrations between 120 and 240μmol/L during first year of life have a positive impact in metabolic control and cognitive functioning during childhood.

Genetically engineered probiotic for the treatment of phenylketonuria (PKU); assessment of a novel treatment in vitro and in the PAHenu2 mouse model of PKU.

Phenylketonuria (PKU) is a genetic disease characterized by the inability to convert dietary phenylalanine to tyrosine by phenylalanine hydroxylase. Given the importance of gut microbes in digestion, a genetically engineered microbe could potentially degrade some ingested phenylalanine from the diet prior to absorption. To test this, a phenylalanine lyase gene from Anabaena variabilis (AvPAL) was codon-optimized and cloned into a shuttle vector for expression in Lactobacillus reuteri 100-23C (pHENOMMenal). Functional expression of AvPAL was determined in vitro, and subsequently tested in vivo in homozygous PAHenu2 (PKU model) mice. Initial trials of two PAHenu2 homozygous (PKU) mice defined conditions for freeze-drying and delivery of bacteria. Animals showed reduced blood phe within three to four days of treatment with pHENOMMenal probiotic, and blood phe concentrations remained significantly reduced (P < 0.0005) compared to untreated controls during the course of experiments. Although pHENOMMenal probiotic could be cultured from fecal samples at four months post treatment, it could no longer be cultivated from feces at eight months post treatment, indicating eventual loss of the microbe from the gut. Preliminary screens during experimentation found no immune response to AvPAL. Collectively these studies provide data for the use of a genetically engineered probiotic as a potential treatment for PKU.

Treatment adherence during childhood in individuals with phenylketonuria: Early signs of treatment discontinuation

IntroductionPhenylketonuria (PKU) is an autosomal recessive disorder characterized by a deficiency in phenylalanine (Phe) hydroxylase activity. Early diagnosis and continuous treatment with a low Phe diet prevents severe neurological and cognitive impairment. Aims1. Analyze how treatment adherence evolves through infancy, childhood, and early adolescence in individuals with PKU. 2. Identify early signs of treatment discontinuation. MethodologyThis longitudinal, retrospective study included 75 children diagnosed through newborn screening, ages 7 to 13years. Data on blood Phe concentration, number of blood samples sent, proportion of samples with Phe concentrations over the recommended range, and number of visits to the metabolism clinic were recorded. Logistic regression analysis was used to identify the variables that predict treatment discontinuation before 13years of age. ResultsA progressive increase in mean blood Phe concentrations with age was identified. The greatest increase occurred between the first and second years of life. By age ten, mean Phe blood concentration of the group was above the recommended range. The proportion of samples with Phe concentrations over the recommended range also increased with age, from an average of 13% during the first year of life to 67% in early adolescence. Sixty-eight percent of the children attended the outpatient clinic and sent samples from birth to the time of the study. Individuals who discontinued follow-up showed significantly higher mean blood Phe concentrations (360 vs. 220.9μmol/L; p=0.004) and the proportion of samples over the recommended range (37% vs. 12% p=0.002) was significantly higher during the second year of life. Mean age for children who discontinued treatment was 5.5years of age. Blood Phe concentration values at 12 to 23months of age and at 6 to 8years of age significantly predicted treatment discontinuation before 13years of age. ConclusionTreatment adherence in PKU diminishes with age. Early signs of treatment discontinuation can be identified during the second year of life, allowing preventive interventions in high risk groups.

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

Assess current management practices of phenylketonuria (PKU) clinics across the United States (US) based on the key treatment metrics of blood phenylalanine (Phe) concentrations and blood Phe testing frequency, as well as patient adherence to their clinic's management practice recommendations. An online survey was conducted with medical professionals from PKU clinics across the US from July to September 2015. Forty-four clinics participated in the survey and account for approximately half of PKU patients currently followed in clinics in the US (Berry et al., 2013). The majority of PKU clinics recommended target blood Phe concentrations to be between 120 and 360μM for all patients; the upper threshold was relaxed by some clinics for adult patients (from 360 to 600μM) and tightened for patients who are pregnant/planning to become pregnant (to 240μM). Patient adherence to these recommendations (percentage of patients with blood Phe below the upper recommended threshold) was age-dependent, decreasing from 88% in the 0-4years age group to 33% in adults 30+ years. Patient adherence to recommendations for blood testing frequency followed a similar trend. Higher staffing intensity (specialists per 100 PKU patients) was associated with better patient adherence to clinics' blood Phe concentrations recommendations. Clinic recommendations of target blood Phe concentrations in the US are now stricter compared to prior years, and largely reflect recent guidelines by the American College of Medical Genetics and Genomics (Vockley et al., 2014). Adherence to recommended Phe concentrations remains suboptimal, especially in older patients. However, despite remaining above the guidelines, actual blood Phe concentrations in adolescents and adults are lower than those reported in the past (Walter et al., 2002; Freehauf et al., 2013). Continued education and support for PKU patients by healthcare professionals, including adequate clinic staffing, are needed to improve adherence. Future research is needed to understand how to improve adherence to reduce the number of patients lost to follow-up, as the findings of this and similar surveys do not address how to keep patients in clinic.

Household financial burden of phenylketonuria and its impact on treatment in China: a cross-sectional study

SummaryBackgroundPhenylketonuria (PKU) is a rare inborn disease, which, untreated, leading to severe neurobehavioral dysfunction. Considering its complexity, the management of PKU may bring a formidable economic burden to parents and caregivers. It is still unknown what the out-of-pocket expenses are for a patient with PKU in China. This paper explores the household financial burden of classical PKU and its impact on Chinese families in a quantitative manner for the first time.MethodsA non-interventional and observational study was conducted at the China-Japan Friendship Hospital, one of the national centers for inherited metabolic disorders in China. The medical and non-medical household financial burdens were consolidated into a questionnaire to evaluate the out-of-pocket costs (OOPCs) of PKU treatment and follow-up.FindingsThe total OOPCs were USD$3766.1 (0y), USD$3795.2 (1–2 ys), USD$4657.7 (3–4 ys), USD$5979.9 (5–8 ys), and USD$5588.7 (9 ys and older) for PKU patients of different age groups. The median economic burden of classical PKU was 75.0 % of total annual family income (range 1.0–779.1 %), and 94.4 % of the families exceeding the threshold considered as catastrophic expenditure. There was a negative correlation between the financial burden and the proportion of time when Phe concentrations were in the desired target range (120–250 μmol/L) in 0–4-ys group (r = -0.474, p = 0.026).ConclusionsThe management of PKU is associated with a severe financial burden on patients’ families, which may lead to insufficient treatment or variation of blood Phe concentration. The current reimbursement policies are as yet inadequate. A national reimbursement system targeting treatment practices for PKU patients and other rare diseases across China is imperative.

Long-term treatment of phenylketonuria with a new medical food containing large neutral amino acids

Background/Objectives:Phenylketonuria (PKU) is an autosomal recessive disease caused by deficient activity of phenylalanine hydroxylase. A low phenylalanine (Phe) diet is used to treat PKU. The diet is very restrictive, and dietary adherence tends to decrease as patients get older. Methods to improve dietary adherence and blood Phe control are continuously under investigation.Subjects/Methods:A new formula Phe-neutral amino acid (PheLNAA) has been tested in this study with the purpose of improving the compliance and lowering blood phenylalanine. The formula has been tested for nitrogen balance, and it is nutritionally complete. It is fortified with more nutritional additives that can be deficient in the PKU diet, such as B12, Biotin, DHA, Lutein and increased levels of large neutral amino acids to help lower blood Phe. The new formula has been tested on 12 patients with a loading test of 4 weeks.Results:Fifty-eight percent of patients had a significant decline in blood Phe concentration from baseline throughout the study. The PheLNAA was well tolerated with excellent compliance and without illnesses during the study.Conclusions:In conclusion, the new formula is suitable for life-long treatment of PKU, and it offers the PKU clinic a new choice for treatment.

Analysis of neonatal hyperphenylalaninemia screening and therapeutic effect in Xuzhou from 2003 to 2015

Objective To investigate the prevalence, clinical classification, treatment and prognosis of neonatal hyperphenylalaninemia(HPA) in Xuzhou area, China. Methods Infants born between July 1, 2003 and July 1, 2015 in Xuzhou area were investigated. Heel blood samples of neonates were collected at 72 hours after birth, and the concentration of blood phenylalanine(Phe) was determined by fluorescent quantitative method in Xuzhou Maternity and Child Health Care Station Neonatal Disease Screening Center. Differential diagnosis was performed in all 265 cases diagnosed as HPA by urinary pterin analysis and dihydropteridine reductase activity determination. The blood Phe concentration and mental development were followed up regularly in infants with HPA. Mutations of phenylalanine hydroxylase (PAH) gene were analyzed by gene sequencing. The relationship between blood Phe concentration and mental development was analyzed by Bivariate correlation analysis. Results (1) The prevalence of HPA in neonates in Xuzhou was l/4 635. Among the 265 confirmed HPA cases, 260 cases(98.11%) had PAH deficiency, including 90(33.96%) classical phenylketonuria(PKU), 84(31.70%) mild PKU and 86(32.45%) mild HPA. The other five patients(1.89%) diagnosed with tetrahydrobiopterin (BH4) deficiency all had 6-pyruvoyl tetrahydropteirn synthase(PTPS) deficiency. (2) Among the 265 HPA cases, 26 cases refused any treatment, including five cases of PTPS deficiency and 21 cases of PKU. Of the five patients with PTPS deficiency, two died and the other three had normal mental and physical development. Twenty-one PKU patients who refused treatment had mental retardation of various degrees. Among 153 PKU patients who received medical treatment, three died and 12 were lost to follow-up. (3) For 138 PKU patients who received dietary treatment and follow-up, the ages at the last visit were two months to 12 years, 116 of them had normal mental development, the remaining 22 patients had mental retardation, and a negative correlation was observed between mental development and the average Phe concentration. (4) Thirty-five patients with PAH deficiency underwent gene sequencing, and 22 kinds of mutations of PAH gene were detected. Conclusions The prevalence of HPA in Xuzhou area is higher than the average national level. With early diagnosis and standard treatment, most of PKU neonates can have normal mental development. Phe level control is an important factor for mental development. Key words: Phenylketonurias; Phenylalanine hydroxylase; Biopterin; Neonatal screening; Intelligence; Treatment outcome

Evaluation of Tetrahydrobiopterin Therapy with Large Neutral Amino Acid Supplementation in Phenylketonuria: Effects on Potential Peripheral Biomarkers, Melatonin and Dopamine, for Brain Monoamine Neurotransmitters.

BackgroundPhenylketonuria (PKU) is due to a defective hepatic enzyme, phenylalanine (Phe) hydroxylase. Transport of the precursor amino acids from blood into the brain for serotonin and dopamine synthesis is reported to be inhibited by high blood Phe concentrations. Deficiencies of serotonin and dopamine are involved in neurocognitive dysfunction in PKU.Objective(1) To evaluate the effects of sapropterin (BH4) and concurrent use of large neutral amino acids (LNAA) on the peripheral biomarkers, melatonin and dopamine with the hypothesis they reflect brain serotonin and dopamine metabolism. (2) To evaluate synergistic effects with BH4 and LNAA. (3) To determine the effects of blood Phe concentrations on the peripheral biomarkers concentrations.MethodsNine adults with PKU completed our study consisting of four 4-week phases: (1) LNAA supplementation, (2) Washout, (3) BH4 therapy, and (4) LNAA with BH4 therapy. An overnight protocol measured plasma amino acids, serum melatonin, and 6-sulfatoxymelatonin and dopamine in first void urine after each phase.Results(1) Three out of nine subjects responded to BH4. A significant increase of serum melatonin levels was observed in BH4 responders with decreased blood Phe concentration. No significant change in melatonin, dopamine or Phe levels was observed with BH4 in the subjects as a whole. (2) Synergistic effects with BH4 and LNAA were observed in serum melatonin in BH4 responders. (3) The relationship between serum melatonin and Phe showed a significant negative slope (p = 0.0005) with a trend toward differing slopes among individual subjects (p = 0.066). There was also a negative association overall between blood Phe and urine 6-sulfatoxymelatonin and dopamine (P = 0.040 and 0.047).ConclusionBlood Phe concentrations affected peripheral monoamine neurotransmitter biomarker concentrations differently in each individual with PKU. Melatonin levels increased with BH4 therapy only when blood Phe decreased. Monitoring peripheral neurotransmitter metabolites may assist in optimizing individualized treatment in PKU.

Glycomacropeptide for nutritional management of phenylketonuria: a randomized, controlled, crossover trial

Background: To prevent cognitive impairment, phenylketonuria requires lifelong management of blood phenylalanine (Phe) concentration with a low-Phe diet. The diet restricts intake of Phe from natural proteins in combination with traditional amino acid medical foods (AA-MFs) or glycomacropeptide medical foods (GMP-MFs) that contain primarily intact protein and a small amount of Phe.Objective: We investigated the efficacy and safety of a low-Phe diet combined with GMP-MFs or AA-MFs providing the same quantity of protein equivalents in free-living subjects with phenylketonuria.Design: This 2-stage, randomized crossover trial included 30 early-treated phenylketonuria subjects (aged 15–49 y), 20 with classical and 10 with variant phenylketonuria. Subjects consumed, in random order for 3 wk each, their usual low-Phe diet combined with AA-MFs or GMP-MFs. The treatments were separated by a 3-wk washout with AA-MFs. Fasting plasma amino acid profiles, blood Phe concentrations, food records, and neuropsychological tests were obtained.Results: The frequency of medical food intake was higher with GMP-MFs than with AA-MFs. Subjects rated GMP-MFs as more acceptable than AA-MFs and noted improved gastrointestinal symptoms and less hunger with GMP-MFs. ANCOVA indicated no significant mean ± SE increase in plasma Phe (62 ± 40 μmol/L, P = 0.136), despite a significant increase in Phe intake from GMP-MFs (88 ± 6 mg Phe/d, P = 0.026). AA-MFs decreased plasma Phe (−85 ± 40 μmol/L, P = 0.044) with stable Phe intake. Blood concentrations of Phe across time were not significantly different (AA-MFs = 444 ± 34 μmol/L, GMP-MFs = 497 ± 34 μmol/L), suggesting similar Phe control. Results of the Behavior Rating Inventory of Executive Function were not significantly different.Conclusions: GMP-MFs provide a safe and acceptable option for the nutritional management of phenylketonuria. The greater acceptability and fewer side effects noted with GMP-MFs than with AA-MFs may enhance dietary adherence for individuals with phenylketonuria. This trial was registered at www.clinicaltrials.gov as NCT01428258.

Hyperphenylalaninemia: From Diagnosis to Therapy

Hyperphenylalaninemia (HPA) is a biochemical condition characterized by mildly or strongly elevated concentrations of the amino acid phenylalanine (Phe) in the blood. HPA is commonly diagnosed by newborn screening. The primary cause of HPA is phenylketonuria (PKU), an inborn error of metabolism characterized by persistently elevated plasma concentrations of Phe secondary to a total or partial deficiency of the liver enzyme phenylalanine hydroxylase. The treatment of babies affected with PKU is based on a Phe-restricted diet, aiming to maintain blood Phe concentrations within a range of 120 to 360 μmol/L to prevent the spectrum of neurological disorders associated with PKU, that is, microcephaly, learning disability, epilepsy, pyramidal and extrapyramidal signs, and behavioral changes. This metabolic disorder mainly affects the white matter (e.g., dysmyelination, demyelination, and hypomyelination) and the cortical-subcortical structures. A delay in starting the dietary treatment, or an inadequate Phe-restricted diet, may relentlessly lead to brain damage.

Clinical relevance of the discrepancy in phenylalanine concentrations analyzed using tandem mass spectrometry compared with ion-exchange chromatography in phenylketonuria

IntroductionMetabolic control of phenylketonuria (PKU) and compliance with the low-phenylalanine (phe) diet are frequently assessed by measuring blood phe concentrations in dried blood spots (DBS) collected by patients instead of plasma phe concentrations. ObjectiveOur objective was to investigate the difference in blood phe concentrations in DBS collected by subjects and analyzed using either a validated newborn screening tandem mass spectrometry (MS/MS) protocol or ion-exchange chromatography (IEC) compared to plasma phe concentrations obtained simultaneously and analyzed using IEC. DesignThree to four fasting blood samples were obtained from 29 subjects with PKU, ages 15–49years. Capillary blood was spotted on filter paper by each subject and the DBS analyzed using both MS/MS and IEC. Plasma was isolated from venous blood and analyzed using IEC. ResultsBlood phe concentrations in DBS analyzed using MS/MS are 28%±1% (n=110, p<0.0001) lower than plasma phe concentrations analyzed using IEC resulting in a blood phe concentration of 514±23μmol/L and a plasma phe concentration of 731±32μmol/L (mean±SEM). This discrepancy is larger when plasma phe is >600μmol/L. Due to the large variability across subjects of 13.2%, a calibration factor to adjust blood phe concentrations is not recommended. Analysis of DBS using IEC reduced the discrepancy to 15±2% lower phe concentrations compared to plasma analyzed using IEC (n=38, p=0.0001). This suggests that a major contributor to the discrepancy in phe concentrations is the analytical method. ConclusionUse of DBS analyzed using MS/MS to monitor blood phe concentrations in individuals with PKU yields significantly lower phe levels compared to plasma phe levels analyzed using IEC. Optimization of current testing methodologies for measuring phe in DBS, along with patient education regarding the appropriate technique for spotting blood on filter paper is needed to improve the accuracy of using DBS to measure phe concentrations in PKU management.

Phenylketonuria (PKU): A problem solved?

Phenylketonuria (PKU) is a rare metabolic disorder characterized by impaired conversion of phenylalanine (Phe) to tyrosine. If left untreated, the resultant accumulation of excess blood Phe can cause physiological, neurological, and intellectual disabilities. The National PKU Alliance (NPKUA) conducted a survey of its membership to assess current health status and interest in new treatments for PKU. Of the 625 survey respondents, less than half (46.7%) reported blood Phe within (120–360μmol/L) — the range recommended by the American College of Medical Genetics and Genomics (ACMG). The survey results also showed that younger (≤18years) individuals were about 3-times as successful in keeping their blood Phe concentrations within the recommended clinical range compared with adults. Blood Phe over 360μmol/L was reported in one-quarter (25.5%) of ≤18year old individuals and almost two-thirds (61.5%) of adults. A little more than half (51.7%) of respondents reported having difficulty in managing their PKU, including the maintenance of a Phe-restricted diet. Individuals with PKU desire new treatments that would allow them to increase their intake of natural protein, discontinue or reduce their intake of medical foods (medical formula and foods modified to be low in protein), improve their mental health (including a reduction in depression and anxiety), and a reduction of their blood Phe concentrations. Respondents preferred oral administration of any newly developed therapies and, in general, disliked therapeutic injections. Injections at home were preferred over injections at a clinic. Payers, government agencies, clinicians, and industry partners should consider patient input when developing and approving new therapies and treatments for PKU.

The challenge of long-term tetrahydrobiopterin (BH4) therapy in phenylketonuria: Effects on metabolic control, nutritional habits and nutrient supply

Background and aimsBH4-sensitive phenylketonuria (PKU) patients relax their phenylalanine (Phe) restricted diet due to increased Phe tolerance, while keeping dried blood Phe concentrations with in the therapeutic range. We aimed to investigate metabolic control, eating habits and nutrient supply under long-term BH4-therapy. Patients and methodsRetrospective analysis of mean dried blood Phe concentrations and their variability, food and nutrient intake in BH4-sensitive patients (n=8, 3f, age 6.0–16.6y) under classical dietary treatment for one year and during the three years after initiation of BH4. ResultsPhe concentrations of BH4-sensitve PKU patients remained within therapeutic range throughout the observation period, independent of therapeutic regime. Under BH4, Phe tolerance increased significantly (493.2±161.8mg/d under classical diet vs 2021.93±897.4mg/d two years under BH4; P=0.004). Variability of Phe concentrations remained unchanged (mean SD; P=1.000). Patients adjust their food choice and significantly increased their intake of cereals, potatoes, dairy products and meat (P=0.019, P=0.016, P=0.016 and P=0.016, respectively). Under diet changes after implementation of BH4 a drop in micronutrient intake (vitamin D, folic acid, iron, calcium, iodine) could be revealed (P=0.005, P<0.001, P=0.004, P=0.001, P=0.003, respectively). ConclusionsBH4-sensitive PKU patients can achieve good metabolic control under an adjuvant BH4- or a BH4 monotherapy. The liberalized diet under BH4 seems to jeopardize the quality of patients' nutrition, and these patients require close follow-up and special nutrition education to minimize the risk for imbalanced diet and nutrient deficiencies.

Management of adult patients with phenylketonuria: survey results from 24 countries.

Phenylketonuria (PKU) is no longer considered merely a pediatric concern; current guidelines recommend life-long treatment. However, information on the adult PKU patient population is scarce. A survey was initiated on behalf of the European PKU Group (EPG) that focused specifically on early-treated adult patients diagnosed by neonatal screening. The online survey was sent via email to 204 healthcare professionals (HCPs) in 33 countries. Eighty-one HCPs from 24 countries responded. The main findings were that the majority of adult patients with PKU in active follow-up are under 30 years of age and are managed in centers that also treat children. Seventy-eight percent of adult PKU patients in follow-up receive treatment, mainly by diet (71 %), with BH4 treatment rarely used in adulthood. Only 26 % of responding HCPs perform routine neurocognitive testing in all their adult patients. There was little consensus regarding target blood phenylalanine (Phe) concentrations, although the majority of respondents reported that their patients achieved blood Phe concentrations below 1200 μmol/l. This survey highlights the need for blood Phe concentration target recommendations and consensus guidelines, more research into adult PKU patient management, and the need to identify those patients lost to follow-up to ensure PKU is managed for life.

Individualized long-term outcomes in blood phenylalanine concentrations and dietary phenylalanine tolerance in 11 patients with primary phenylalanine hydroxylase (PAH) deficiency treated with Sapropterin-dihydrochloride.

We analyzed long-term sustainability of improved blood Phenylalanine (Phe) control and changes to dietary Phe tolerance in 11 patients (1 month to 16 years), with various forms of primary PAH deficiency (classic, moderate, severe phenylketonuria [PKU], mild hyperphenylalaninemia [HPA]), who were treated with 15-20mg/kg/d Sapropterin-dihydrochloride during a period of 13-44 months. 7/11 patients had a sustainable, significant reduction of baseline blood Phe concentrations and 6 of them also had an increase in mg/kg/day Phe tolerance. In 2 patients with mild HPA, blood Phe concentrations remained in the physiologic range even after a 22 and 36% increase in mg/kg/day Phe tolerance and an achieved Phe intake at 105% and 268% of the dietary reference intake (DRI) for protein. 2 of these responders had classic PKU. 1 patient with mild HPA who started treatment at 2 months of life, had a significant and sustainable reduction in pretreatment blood Phe concentrations, but no increase in the mg/kg/day Phe tolerance. An increase in Phe tolerance could only be demonstrated when expressing the patient's daily Phe tolerance with the DRI for protein showing an increase from 58% at baseline to 78% of normal DRI at the end of the observation. Long-term follow-up of patients with an initial response to treatment with Sapropterin is essential to determine clinically meaningful outcomes. Phenylalanine tolerance should be expressed in mg/kg/day and/or % of normal DRI to differentiate medical therapy related from physiologic growth related increase in daily Phe intake.