Rationale for the German recommendations for phenylalanine level control in phenylketonuria 1997

Intake Modalities of Amino Acid Supplements: A Real-World Data Collection from Phenylketonuria Patients

BACKGROUND

To achieve a normal nutritional status, patients suffering from phenylketonuria (PKU) are typically prescribed amino acid (AA) supplements with low or no phenylalanine (Phe) content. Studies evaluating patient preferences regarding the intake modalities of AA supplements are limited. This study aimed to collect real-world data regarding prescription adherence and intake modalities of AA supplements reported by PKU patients while monitoring metabolic control.

METHODS

This cross-sectional study included 33 PKU patients (16 female and 17 male) with a mean age of 27.2 years. Questionnaires were provided to assess information on AA supplement intake, such as prescription adherence rate, frequency and timing of administration, supplement formulation, and combination with food or drinks. Plasma phenylalanine levels were monitored during the study period.

RESULTS

51.5% (n = 17) of patients reported to lay within an adherence range of 75-100%. The majority of patients consumed AA supplements twice daily, with breakfast (87.9%) and afternoon snacks (51.5%). Powder supplements were most commonly used (72.7%) and often combined with milk and/or fruit juices (45.4%).

CONCLUSIONS

Despite the known concerns related to treatment compliance among PKU adolescents and adults, most of the study participants reported a high level of adherence to AA supplement prescription. The personalized dietary regimens followed by the patients included in the current study represent a treatment approach that might be worth trying in non-compliant patients.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Impact of pregnancy planning and preconceptual dietary training on metabolic control and offspring's outcome in phenylketonuria

To prevent maternal phenylketonuria (PKU) syndrome low phenylalanine concentrations (target range, 120-360 μmol/L) during pregnancy are recommended for women with PKU. We evaluated the feasibility and effectiveness of current recommendations and identified factors influencing maternal metabolic control and children's outcome. Retrospective study of first successfully completed pregnancies of 85 women with PKU from 12 German centers using historical data and interviews with the women. Children's outcome was evaluated by standardized IQ tests and parental rating of child behavior. Seventy-four percent (63/85) of women started treatment before conception, 64% (54/85) reached the phenylalanine target range before conception. Pregnancy planning resulted in earlier achievement of the phenylalanine target (18 weeks before conception planned vs. 11 weeks of gestation unplanned, p < 0.001) and lower plasma phenylalanine concentrations during pregnancy, particularly in the first trimester (0-7 weeks of gestation: 247 μmol/L planned vs. 467 μmol/L unplanned, p < 0.0001; 8-12 weeks of gestation: 235 μmol/L planned vs. 414 μmol/L unplanned, p < 0.001). Preconceptual dietary training increased the success rate of achieving the phenylalanine target before conception compared to women without training (19 weeks before conception vs. 9 weeks of gestation, p < 0.001). The majority (93%) of children had normal IQ (mean 103, median age 7.3 years); however, IQ decreased with increasing phenylalanine concentration during pregnancy. Good metabolic control during pregnancy is the prerequisite to prevent maternal PKU syndrome in the offspring. This can be achieved by timely provision of detailed information, preconceptual dietary training, and careful planning of pregnancy.

Optical Coherence Tomography to Assess Neurodegeneration in Phenylalanine Hydroxylase Deficiency

In phenylalanine hydroxylase (PAH) deficiency, an easily feasible method to access the progression of neurodegeneration is warranted to contribute to current discussions on treatment indications and targets. The objective of the present study was to investigate whether optical coherence tomography (OCT) measures as markers of neurodegeneration differ between patients with PAH deficiency and healthy controls (HCs) according to phenotype and metabolic control. In this single-center cross-sectional study, 92 patients with different phenotypes of PAH deficiency [PAH deficiency not requiring treatment, early treated phenylketonuria (ETPKU), and late-diagnosed phenylketonuria (PKU)] compared with 76 HCs were examined using spectral-domain OCT. Indices of phenylalanine elevation and variability were correlated with OCT parameters. Late-diagnosed PKU patients showed reduced peripapillary retinal nerve fiber layer (pRNFL) thickness and combined ganglion cell and inner plexiform layer (GCIPL) volume. Adult ETPKU patients were found to have lower GCIPL volume (p = 0.016), which correlated with the indices of phenylalanine control. In pediatric ETPKU patients with poor metabolic control, pRNFL was significantly reduced (p = 0.004). Patients with PAH deficiency not requiring treatment did not exhibit retinal degeneration. Inner nuclear layer (INL) was significantly increased in the pediatric ETPKU patients, driven by those with current poor metabolic control (p = 0.006). Our data provide evidence of retinal neuroaxonal degeneration and INL swelling, depending on the phenotype, current age, and metabolic control. These findings suggest that OCT is suitable to investigate neurodegeneration in PKU and we propose OCT as a sensitive, reliable, safe, low-burden, and low-cost examination for future multicenter studies.

Preventing maternal phenylketonuria (PKU) syndrome: important factors to achieve good metabolic control throughout pregnancy

Background

Insufficient metabolic control during pregnancy of mothers with phenylketonuria (PKU) leads to maternal PKU syndrome, a severe embryo-/fetopathy. Since maintaining or reintroducing the strict phenylalanine (Phe) limited diet in adults with PKU is challenging, we evaluated the most important dietary and psychosocial factors to gain and sustain good metabolic control in phenylketonuric women throughout pregnancy by a questionnaire survey with 38 questions concerning therapy feasibility. Among them, the key questions covered 5 essential items of PKU care as follows: General information about maternal PKU, PKU training, diet implementation, individual metabolic care, personal support. In addition, all participating PKU mothers were asked to estimate the quality of their personal metabolic control of the concluded pregnancies. 54 PKU mothers with 81 pregnancies were approached at 12 metabolic centers in Germany and Austria were included. According to metabolic control, pregnancies of PKU women were divided in two groups: group “ideal” (not more than 5% of all blood Phe concentrations during pregnancy > 360 µmol/l; n = 23) and group “suboptimal” (all others; n = 51).

Results

The demand for support was equally distributed among groups, concerning both amount and content. Personal support by the direct social environment (partner, family and friends) (“suboptimal” 71% vs “ideal” 78%) as well as individual metabolic care by the specialized metabolic center (both groups around 60%) were rated as most important factors. The groups differed significantly with respect to the estimation of the quality of their metabolic situation (p < 0.001). Group “ideal” presented a 100% realistic self-assessment. In contrast, group “suboptimal” overestimated their metabolic control in 53% of the pregnancies. Offspring of group “suboptimal” showed clinical signs of maternal PKU-syndrome in 27%.

Conclusion

The development of training programs by specialized metabolic centers for females with PKU in child bearing age is crucial, especially since those mothers at risk of giving birth to a child with maternal PKU syndrome are not aware of their suboptimal metabolic control. Such programs should provide specific awareness training for the own metabolic situation and should include partners and families.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02108-5.

Cardiac Magnetic Resonance Reveals Incipient Cardiomyopathy Traits in Adult Patients With Phenylketonuria

Background Phenylketonuria is the most common inborn error of amino acid metabolism, where oxidative stress and collateral metabolic abnormalities are likely to cause cardiac structural and functional modifications. We aim herein to characterize the cardiac phenotype of adult subjects with phenylketonuria using advanced cardiac imaging. Methods and Results Thirty-nine adult patients with phenylketonuria (age, 30.5±8.7 years; 10-year mean phenylalanine concentration, 924±330 µmol/L) and 39 age- and sex-matched healthy controls were investigated. Participants underwent a comprehensive cardiac magnetic resonance and echocardiography examination. Ten-year mean plasma levels of phenylalanine and tyrosine were used to quantify disease activity and adherence to treatment. Patients with phenylketonuria had thinner left ventricular walls (septal end-diastolic thickness, 7.0±17 versus 8.8±1.7 mm [P<0.001]; lateral thickness, 6.1±1.4 versus 6.8±1.2 mm [P=0.004]), more dilated left ventricular cavity (end-diastolic volume, 87±14 versus 80±14 mL/m² [P=0.0178]; end-systolic volume, 36±9 versus 29±8 mL/m² [P<0.001]), lower ejection fraction (59±6% versus 64±6% [P<0.001]), reduced systolic deformation (global circumferential strain, -29.9±4.2 % versus -32.2±5.0 % [P=0.027]), and lower left ventricular mass (38.2±7.9 versus 47.8±11.0 g/m² [P<0.001]). T1 native values were decreased (936±53 versus 996±26 ms [P<0.001]), with particular low values in patients with phenylalanine >1200 µmol/L (909±48 ms). Both mean phenylalanine (P=0.013) and tyrosine (P=0.035) levels were independently correlated with T1; and in a multiple regression model, higher phenylalanine levels and higher left ventricular mass associate with lower T1. Conclusions Cardiac phenotype of adult patients with phenylketonuria reveals some traits of an early-stage cardiomyopathy. Regular cardiology follow-up, tighter therapeutic control, and prophylaxis of cardiovascular risk factors, in particular dyslipidemia, are recommended.

Health economic burden of patients with phenylketonuria (PKU) - A retrospective study of German health insurance claims data

This retrospective matched-cohort analysis compared health-economic burdens of adults (≥18 years; n = 377) with phenylketonuria (PKU) and age/gender-matched non-PKU controls (n = 3770) in Germany. Healthcare costs and resource-utilization were analyzed for the year 2015. Differences between groups were tested using 95% CI of mean differences (MD). PKU patients had significantly higher mean costs in total (MD €3307, 95% CI €1736–€4879), for pharmaceuticals (MD €1912, 95% CI €1195–€2629) [including dietary amino-acid supplements (MD €1268, 95% CI €864–€1672)], and outpatient costs (MD €395, 95% CI €115–€675). Inpatient costs (MD €904, 95% CI -€293 to €2100) and costs for aids and remedies (MD €97, 95% CI -€10 to €203) were also higher in PKU patients. PKU patients had more outpatient visits and stayed longer in hospital. Adult PKU patients incur higher total healthcare costs than non-PKU controls, especially regarding pharmaceuticals and outpatient costs, and more frequent resource-utilization, resulting in higher health-economic burden for the statutory healthcare system.

Everyday Life, Dietary Practices, and Health Conditions of Adult PKU Patients: A Multicenter, Cross-Sectional Study

BACKGROUND

Only few data on dietary management of adult phenylketonuria (PKU) patients are published.

OBJECTIVES

This study aimed to assess living situation, dietary practices, and health conditions of early-treated adult PKU patients.

METHODS

A total of 183 early-treated PKU patients ≥18 years from 8 German metabolic centers received access to an online survey, containing 91 questions on sociodemographic data, dietary habits, and health conditions.

RESULTS

144/183 patients (66% females) completed the questionnaire. Compared with German population, the proportion of single-person households was higher (22 vs. 47%), the rate of childbirth was lower (1.34 vs. 0.4%), but educational and professional status did not differ. 82% of the patients adhered to a low-protein diet, 45% consumed modified low-protein food almost daily, and 84% took amino acid mixtures regularly. 48% of the patients never interrupted diet, and 14% stopped diet permanently. 69% of the patients reported to feel better with diet, and 91% considered their quality of life at least as good. The prevalence of depressive symptoms was high (29%) and correlated significantly to phenylalanine blood concentrations (p = 0.046). However, depressive symptoms were only mild in the majority of patients.

CONCLUSION

This group of early-treated adult German PKU patients is socially well integrated, reveals a surprisingly high adherence to diet and amino acid intake, and considers the restrictions of diet to their daily life as low.

Morning specimen is not representative of metabolic control in Tunisian children with phenylketonuria: a repeated cross-sectional study

Objective and methods To evaluate variation of capillary phenylalanine concentrations over the day in patients treated for phenylketonuria and the reliability of the morning sample to assess metabolic control, we conducted a repeated cross-sectional study in 25 Tunisian patients on phenylalanine-low diet. For each patient, we collected nine capillary samples over the day. Phenylalanine was dosed by fluorimetry. Results There was a wide variability of phenylalanine concentrations over the day (p<0.001). Compared to morning sample, phenylalanine concentration was significantly lower before lunch (p=0.038), after lunch (p=0.025), before dinner (p<0.001), after dinner (p=0.035) and at 4:00 a.m. (p=0.011). Compared to the 24 h sampling, the morning sample had a 68% to identify unbalanced patients. 60% of patients, had peak phenylalanine concentration after the morning. Half of the patients with normal morning phenylalanine concentration had low phenylalanine values over 8-20 h. Percentages of high phenylalanine concentrations over the last semester were higher in patients with poor metabolic control over the 24 h (21% ± 43 vs. 0% ± 9%); p=0.043. Conclusion A single morning sample gives an incomplete information on metabolic control in phenylketonuric patients. Using four pre-prandial samples on the day should be considered as alternative in patients with good metabolic control.

Phenylketonuria, co-morbidity, and ageing: A review

Phenylketonuria (PKU) is a metabolic condition which, left untreated, results in severe and irreversible brain damage. Newborn screening and the development of the low phenylalanine (Phe) diet have transformed the outcomes for people with PKU. Those who have benefited from early treatment are now approaching their fifth and sixth decade. It is therefore timely to consider multi-morbidity in PKU and the effects of ageing, in parallel with the wider benefits of emerging treatment options in addition to dietary relaxation. We have conducted the first literature review of co-morbidity and ageing in the context of PKU. Avenues explored have emerged from limited study of multi-morbidity to date and the knowledge and critical enquiry of the authors. Findings suggest PKU to have a wider impact than brain development, and result in several intriguing questions that require investigation to attain the best outcomes for people with PKU in adulthood moving through to older age. We recognise the difficulty in studying longitudinal outcomes in rare diseases and emphasise the necessity to develop PKU registries and cohorts that facilitate well-designed studies to answer some of the questions raised in this review. Whilst awaiting new information in these areas we propose that clinicians engage with patients to make personalised and well-informed decisions around Phe control and assessment for co-morbidity.

Lower plasma cholesterol, LDL-cholesterol and LDL-lipoprotein subclasses in adult phenylketonuria (PKU) patients compared to healthy controls: results of NMR metabolomics investigation

Background

Phenylketonuria (PKU; OMIM#261600) is a rare metabolic disorder caused by mutations in the phenylalanine hydroxylase (PAH) gene resulting in high phenylalanine (Phe) in blood and brain. If not treated early this results in intellectual disability, behavioral and psychiatric problems, microcephaly, motor deficits, eczematous rash, autism, seizures, and developmental problems. There is a controversial discussion of whether patients with PKU have an additional risk for atherosclerosis due to interference of Phe with cholesterol synthesis and LDL-cholesterol regulation. Since cholesterol also plays a role in membrane structure and myelination, better insight into the clinical significance of the impact of Phe on lipoprotein metabolism is desirable. In 22 treated PKU patients (mean age 38.7 years) and 14 healthy controls (mean age 35.2 years), we investigated plasma with NMR spectroscopy and quantified 105 lipoprotein parameters (including lipoprotein subclasses) and 24 low molecular weight parameters. Analysis was performed on a 600 MHz Bruker AVANCE IVDr spectrometer as previously described.

Results

Concurrent plasma Phe in PKU patients showed a wide range with a mean of 899 μmol/L (50–1318 μmol/L). Total cholesterol and LDL-cholesterol were significantly lower in PKU patients versus controls: 179.4 versus 200.9 mg/dL (p < 0.02) and 79.5 versus 104.1 mg/dL (p < 0.0038), respectively. PKU patients also had lower levels of 22 LDL subclasses with the greatest differences in LDL2 Apo-B, LDL2 Particle Number, LDL2-phospholipids, and LDL2-cholesterol (p < 0.0001). There was a slight negative correlation of total cholesterol and LDL-cholesterol with concurrent Phe level. VLDL5-free cholesterol, VLDL5-cholesterol, VLDL5-phospholipids, and VLDL4-free cholesterol showed a significant (p < 0.05) negative correlation with concurrent Phe level. There was no difference in HDL and their subclasses between PKU patients and controls. Tyrosine, glutamine, and creatinine were significantly lower in PKU patients compared to controls, while citric and glutamic acids were significantly higher.

Conclusions

Using NMR spectroscopy, a unique lipoprotein profile in PKU patients can be demonstrated which mimics a non-atherogenic profile as seen in patients treated by statins.

Management of three preterm infants with phenylketonuria

Providing adequate amounts of protein in preterm infants suffering from a metabolic disease that requires a reduced intake of natural protein is challenging. Phenylketonuria (PKU) is an inborn error of metabolism affecting the enzymatic conversion of phenylalanine to tyrosine. The dietary treatment of PKU aims to lower phenylalanine concentrations in the blood by implementing a low-phenylalanine diet restrictive in natural protein. We describe the nutritional management of three preterm infants, two with very low birth weight, with PKU detected by newborn screening. All three infants tolerated high amounts of phenylalanine; two were breastfed unrestrictedly during late prematurity. We show that nutrition of preterm infants with PKU according to recommendations of early and intensive nutrition with a high intake of protein is feasible even in infants with impaired enteral feeding. Due to a high phenylalanine tolerance of PKU infants during prematurity, there is no need for a phenylalanine-free parenteral amino acid mixture. During the catabolic state of prematurity preterm infants with PKU have phenylalanine requirements comparable to healthy preterm infants.

The cardiovascular phenotype of adult patients with phenylketonuria

BACKGROUND

Patients with Phenylketonuria (PKU) are exposed to multiple cardiovascular risk factors, but the clinical significance of these abnormalities is yet unknown. The purpose of this study was to characterize the cardiovascular phenotype in adult patients with PKU by clinical and dietary data, measurements of biochemical markers, and non-invasive examination of vascular functions.

RESULTS

Twenty-three adult patients with PKU (age: 18-47 y; 30.8 ± 8.4 y) and 28 healthy controls (age: 18-47 y; 30.1 ± 9.1 y) were included in this study. PKU patients had significantly higher systolic and diastolic blood pressure, increased resting heart rate and a higher body mass index. Total cholesterol and non-HDL cholesterol levels were significantly increased in PKU patients, whereas plasma levels of HDL cholesterol and its subfraction HDL2 (but not HDL3) were significantly decreased. The inflammatory markers C-reactive protein and serum amyloid A protein and the serum oxidative stress marker malondialdehyde were significantly higher in patients with PKU. Venous occlusion plethysmography showed marked reduction in post-ischemic blood flow and the carotid to femoral pulse wave velocity was significantly increased demonstrating endothelial dysfunction and increased vascular stiffness.

CONCLUSIONS

This study shows that the cardiovascular phenotype of adult PKU patients is characterized by an accumulation of traditional cardiovascular risk factors, high levels of inflammatory and oxidative stress markers, endothelial dysfunction and vascular stiffness. These data indicate the need for early cardiovascular risk reduction in patients with PKU.

Clinical burden of illness in patients with phenylketonuria (PKU) and associated comorbidities - a retrospective study of German health insurance claims data

BACKGROUND

Phenylketonuria (PKU) is an inherited deficiency in the enzyme phenylalanine hydroxylase (PAH), which, when poorly-managed, is associated with clinical features including deficient growth, microcephaly, seizures, and intellectual impairment. The management of PKU should start as soon as possible after diagnosis to prevent irreversible damage and be maintained throughout life. The aim of this study was to assess the burden of illness in PKU patients in general and in PKU patients born before and after the introduction of newborn screening in Germany.

METHODS

This retrospective matched cohort analysis used the Institut für angewandte Gesundheitsforschung Berlin (InGef) research database containing anonymized healthcare claims of approximately 4 million covered lives. PKU patients were compared with matched controls from the general population within the same database (1:10 ratio via direct, exact matching on age and gender without replacement). PKU patients were included if they were aged ≥18 years on 01/01/15 and were continuously enrolled from 01/01/10 to 31/12/15. The 50 most commonly reported comorbidities and 50 most commonly prescribed medications in the PKU population were analyzed. Differences between groups were tested using 95% confidence interval (CI) of prevalence ratio (PR) values.

RESULTS

The analysis included 377 adult PKU patients (< 5 of which were receiving sapropterin dihydrochloride) and 3,770 matched controls. Of the 50 most common comorbidities in the PKU population, those with a statistically significant PR > 1.5 vs controls included major depressive disorders (PR = 2.3), chronic ischemic heart disease (PR = 1.7), asthma (PR = 1.7), dizziness and giddiness (PR = 1.8), unspecified diabetes mellitus (PR = 1.7), infectious gastroenteritis and colitis (PR = 1.7), and reaction to severe stress and adjustment disorders (PR = 1.6). The most commonly prescribed Anatomical Therapeutic Chemical (ATC) subcodes among PKU patients (vs the control population) are for systemic antibacterials (34.7% vs 32.8%), anti-inflammatory and antirheumatic (29.4% vs 27.5%), renin-angiotensin agents (30.0% vs 27.0%), acid-related disorders (29.4% vs 20.2%), and beta-blockers (24.9% vs 19.9%).

CONCLUSION

The overall clinical burden on patients with PKU is exacerbated by a significantly higher risk of numerous comorbidities and hence, prescribing of the requisite medication, both for recognized (e.g. major depressive disorders) and more unexpected comorbidities (e.g. ischemic heart disease).

Children and adolescents with phenylketonuria display fluctuations in their blood phenylalanine levels

AIM

This study examined the impact of fluctuations in metabolic control on the intelligence quotient (IQ) of children and adolescents with early, continuously treated phenylketonuria (PKU).

METHODS

This was a clinic-based study carried out at University Hospital Munster, Germany, from 2015 to 2017. We investigated 49 patients (28 boys) with early treated PKU, who were aged 6-18 years with a mean age of 11.2 ± 4.1 years. All the patients were on a continuous phenylalanine-restricted diet. Of the 49 patients, 29 (18 boys) had classic PKU and 21 patients (11 girls) had mild PKU. The patients' blood phenylalanine levels were assessed every week for 26 weeks and analysed for fluctuations, indicated by the standard deviation of the individual blood phenylalanine levels. We also assessed the concurrent Full Scale IQ (FSIQ) of the patients.

RESULTS

In patients with classic PKU, FSIQ was negatively correlated with blood phenylalanine levels, but not with level fluctuations. In patients with mild PKU, FSIQ was not correlated with blood phenylalanine levels, but was negatively correlated with level fluctuations.

CONCLUSION

The blood phenylalanine levels of patients with mild PKU showed minor interindividual differences, which may have allowed fluctuations to exert a negative effect on the FSIQ.

Molecular genetics of a cohort of 635 cases of phenylketonuria in a consanguineous population

Phenylketonuria (PKU) is an inborn error of amino acid metabolism caused by mutations in the phenylalanine hydroxylase (PAH) gene, characterized by intellectual deficit and neuropsychiatric complications in untreated patients with estimated frequency of about one in 10,000 to 15,000 live births. PAH deficiency can be detected by neonatal screening in nearly all cases with hyperphenylalaninemia on a heel prick blood spot. Molecular testing of the PAH gene can then be performed in affected family members. Herein, we report molecular study of 635 patients genetically diagnosed with PKU from all ethnicities in Iran. The disease-causing mutations were found in 611 (96.22%) of cases. To the best of our knowledge, this is the most comprehensive molecular genetics study of PKU in Iran, identifying 100 distinct mutations in the PAH gene, including 15 previously unreported mutations. Interestingly, we found unique cases of PKU with uniparental disomy, germline mosaicism, and coinheritance with another Mendelian single-gene disorder that provides new insights for improving the genetic counseling, prenatal diagnosis (PND), and/or pre-implantation genetic diagnosis (PGD) for the inborn error of metabolism group of disorders.

Sapropterin treatment does not enhance the health-related quality of life of patients with phenylketonuria and their parents

AIM

Sapropterin causes reductions in blood phenylalanine concentrations in sensitive patients with phenylketonuria (PKU). We examined whether the subsequent relaxation of dietary restrictions influenced the quality of life (QoL) of patients and parents.

METHODS

The study cohort comprised 112 patients with PKU followed at the metabolic centre at Münster University Children's Hospital, Germany, from 2012 to 2015. A sapropterin response was defined as a ≥30% reduction in blood phenylalanine levels. The QoL of 38 children and adolescents from the study cohort, with a mean age of 12.4 (range 6.6-18.7) years, was assessed in an outpatient setting and 49 parents of children with PKU also commented on their child's QoL and their own. The participants' QoL was assessed before the start of therapy, and again after six months, using self-report questionnaires.

RESULTS

After six months of continuous therapy or diet, QoL was largely unchanged in the patients, according to their self-reports and the parental reports. QoL also remained unchanged in the parents.

CONCLUSION

Sapropterin did not seem to improve QoL in PKU patients and their parents. Patients with PKU had already reached high levels of QoL following classic diets, and these levels were not easily improved by sapropterin.

Ten years of specialized adult care for phenylketonuria - a single-centre experience

Background

Specialized adult care of phenylketonuria (PKU) patients is of increasing importance. Adult outpatient clinics for inherited errors of metabolism can help to achieve this task, but experience is limited. Ten years after establishment of a coordinated transition process and specialised adult care for inherited metabolic diseases, adult PKU care was evaluated with respect to metabolic control, therapy satisfaction, life satisfaction, sociodemographic data, economical welfare as well as pregnancy outcome.

Methods

All PKU patients transferred from paediatric to adult care between 2005 and 2015 were identified. A retrospective data analysis and a cross-sectional survey in a sub-cohort of 30 patients including a questionnaire for assessing quality of life (FLZm) were performed as a single-centre investigation at the metabolic department of the University Hospital Leipzig, Germany. For statistical analysis, Mann-Whitney-U-test, t-test for independent samples, ANOVA and chi square test were used as appropriate.

Results

96 PKU patients (56 females/40 males; median age 32 years, range 18–62) were included. In the last 3-year period, 81 % of the transferred patients still kept contact to the adult care centre. Metabolic control was stable over the evaluation period and dried blood phenylalanine concentrations mostly remained within the therapeutic range (median 673.0 μmol/l, range 213.0–1381.1). Sociodemographic data, economical welfare and life satisfaction data were comparable to data from the general population. However, differences could be revealed when splitting the cohort according to time of diagnosis and to management during childhood. 83 % of the PKU adults were satisfied with the transition process and current adult care. 25 completed pregnancies were supervised; three newborns, born after unplanned pregnancy, showed characteristic symptoms of maternal PKU syndrome.

Conclusions

Continuous care for adult PKU patients in a specialized outpatient clinic is successful, leading to good to satisfactory metabolic control and social outcomes. Uninterrupted good metabolic treatment throughout childhood and adolescence positively influences educational, professional and economic success in later life. Further effort in specialized paediatric and adult metabolic care is needed to prevent loss of follow-up and to support the recommended life-long treatment and/or care.

Effect of dietary regime on metabolic control in phenylketonuria: Is exact calculation of phenylalanine intake really necessary?

Background

A phenylalanine (Phe) restricted dietary management is required in phenylketonuria (PKU) to maintain good metabolic control. Nevertheless, five different models of dietary regimes, which differ in their accuracy of Phe documentation, are used. To investigate the effect of the dietary regime on metabolic control, a multicenter evaluation was performed.

Patients/Methods

149 patients (max. 800 mg Phe-intake/day; 108 children aged 1–9 years and 41 adolescents aged 10–15 years) could be included. They were separated according to age and dietary regime, revealed by a questionnaire on dietary habits. Dietary regimes vary from daily strict calculation of all Phe-intake (group 1) to a rather loose regime only estimating Phe-intake and including high protein food (group 5). Data were analyzed with respect to metabolic control (Phe-concentrations, Phe-concentrations above upper recommended limit during 6 months before the interview), Phe-intake (mg/day) and age (years).

Results

Median Phe-concentrations in children did not differ significantly among diet groups (group 1: 161; 2: 229, 3: 236, 4: 249, 5: 288 μmol/l, p = 0.175). However, exact daily Phe calculation led to significantly lower percentage of Phe concentrations above the upper recommended limit (group 1: 17, 2: 50, 3: 42, 4: 50, 5: 75%, p = 0.035). All included patients showed good to acceptable metabolic control. Patients on the dietary regime with the least accuracy, consuming also high protein foods, showed the poorest metabolic control. Median Phe concentrations of all other groups remained within recommended ranges, including from groups not calculating special low protein foods, fruit and vegetables and using a simplified system of recording Phe-intake.

In adolescents no significant differences among diet groups were revealed.

Conclusion

Exact calculation of Phe content of all food is not necessary to achieve good metabolic control in children and adolescents with PKU. Excluding special low protein food, as well as fruit and vegetables from calculation of Phe-intake has no impact on metabolic control. However including protein rich food into the diet and simply estimating all Phe-intake appears insufficient. The simplification of dietary regime may be helpful in enhancing acceptability and feasibility.

Clinical therapeutics for phenylketonuria

Phenylketonuria was amongst the first of the metabolic disorders to be characterised, exhibiting an inborn error in phenylalanine metabolism due to a functional deficit of the enzyme phenylalanine hydroxylase. It affects around 700,000 people around the globe. Mutations in the gene coding for hepatic phenylalanine hydroxylase cause this deficiency resulting in elevated plasma phenylalanine concentrations, leading to cognitive impairment, neuromotor disorders and related behavioural symptoms. Inception of low phenylalanine diet in the 1950s marked a revolution in the management of phenylketonuria and has since been a vital element of all therapeutic regimens. However, compliance to dietary therapy has been found difficult and newer supplement approaches are being examined. The current development of gene therapy and enzyme replacement therapeutics may offer promising alternatives for the management of phenylketonuria. This review outlines the pathological basis of phenylketonuria, various treatment regimes, their associated challenges and the future prospects of each approach. Briefly, novel drug delivery systems which can potentially deliver therapeutic strategies in phenylketonuria have been discussed.

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.

Unrestricted fruits and vegetables in the PKU diet: a 1-year follow-up

Phenylketonuria (PKU) therapy demands phenylalanine (Phe) calculation. In most countries, almost all food is taken into account, even fruits and vegetables. We investigated whether unrestricted consumption of fruits and vegetables negatively influences metabolic control. Nineteen PKU children (2-10 years) started with 2 weeks of free or restricted fruit and vegetable intake. After 2 weeks, the regime changed from free to restricted or restricted to free (cross-over design). Over the first 4 weeks, dried blood Phe concentration was measured, fruit and vegetable consumption recorded and nutrient intake calculated from diet records. Thereafter the diet was changed to free use of fruits and vegetables for all patients. Six and 12 months later, diet and Phe concentrations were monitored. Median Phe intake increased significantly by 65 mg/day (week 4, P<0.001), 68 mg/day (month 6, P<0.001) and 70 mg/day (month 12, P<0.001). Dried blood Phe concentrations remained stable (P=0.894), as did the frequency of Phe concentrations above the recommended range (P=0.592). In conclusion, PKU diet liberalization for fruits and vegetables seems unproblematic.

Fluctuations in phenylalanine concentrations in phenylketonuria: a review of possible relationships with outcomes

Fluctuations in blood phenylalanine concentrations may be an important determinant of intellectual outcome in patients with early and continuously treated phenylketonuria (PKU). This review evaluates the studies on phenylalanine fluctuations, factors affecting fluctuations, and if stabilizing phenylalanine concentrations affects outcomes, particularly neurocognitive outcome. Electronic literature searches of Embase and PubMed were performed for English-language publications, and the bibliographies of identified publications were also searched. In patients with PKU, phenylalanine concentrations are highest in the morning. Factors that can affect phenylalanine fluctuations include age, diet, timing and dosing of protein substitute and energy intake, dietary adherence, phenylalanine hydroxylase genotype, changes in dietary phenylalanine intake and protein metabolism, illness, and growth rate. Even distribution of phenylalanine-free protein substitute intake throughout 24h may reduce blood phenylalanine fluctuations. Patients responsive to and treated with 6R-tetrahydrobiopterin seem to have less fluctuation in their blood phenylalanine concentrations than controls. An increase in blood phenylalanine concentration may result in increased brain and cerebrospinal fluid phenylalanine concentrations within hours. Although some evidence suggests that stabilization of blood phenylalanine concentrations may have benefits in patients with PKU, more studies are needed to distinguish the effects of blood phenylalanine fluctuations from those of poor metabolic control.

Influence of PAH Genotype on Sapropterin Response in PKU: Results of a Single-Center Cohort Study

OBJECTIVE

Identifying phenylalanine hydroxylase (PAH) mutations associated with sapropterin response in phenylketonuria (PKU) would be an advantageous means to determine clinical benefit to sapropterin therapy.

METHODS

Sapropterin response, defined as a ≥30 % reduction in phenylalanine (Phe) levels after a dose of 10 mg/kg/day sapropterin for week one and 20 mg/kg/day for week two in 112 PKU patients aged 4-45 years, was assessed in an outpatient setting. PAH was sequenced in all patients. Mutations were correlated with sapropterin response. Dietary Phe intake was increased over a 6-week period in responsive patients.

RESULTS

Forty-six of 112 patients were sapropterin responsive. Genotypes p.[L48S];[L48S] and p.[Y414C];[Y414C] were always associated with response at a low dose. The mutation Y414C (present on 16 alleles) was most frequently associated with response. Patients with presence of the mutation L48S on at least one allele (12 alleles in 7 patients) always showed response to sapropterin. Responsive patients had a mean Phe tolerance increase of 189 % (range 11-742 %). In the 66 nonresponders, mutations R408W (38 alleles) and IVS12+1G>A (18 alleles) were detected most frequently. Genotypes [IVS12+1G>A];[IVS12+1G>A], p.[L348V];[R408W], p.[P281L];[P281L], p.[R158Q];[R408W], and p.[R261Q];[R408W] were always associated with nonresponse.

CONCLUSION

Data from the study contributes to growing evidence of the relationship between PAH genotype and PKU phenotype. In most cases, response to sapropterin therapy cannot be predicted based on the presence of a single mutation on one allele alone, although the complete PAH genotype may help to predict sapropterin responsiveness in PKU patients.

Chronic kidney disease in adolescent and adult patients with phenylketonuria

OBJECTIVES

A lifelong phenylalanine-restricted diet with supplementation of a phenylalanine-free amino acid formula is recommended in patients with phenylketonuria (PKU). The effect of a long-term PKU diet on renal function and blood pressure has not been investigated yet.

DESIGN

We analyzed renal function in 67 patients with PKU, aged 15-43 years, by measuring glomerular filtration rate (GFR) and effective renal plasma flow by isotope clearance ((51)Cr-EDTA, (123)J-Hippuran), estimated GFR, blood retention parameters, urinary protein and electrolyte excretion. Renal ultrasound and 24 h ambulatory blood pressure monitoring were performed additionally. Patients were divided into three groups according to their: 1) current diet (CD), i.e., daily protein intake: ICD <0.8 g/kg, IICD 0.8-1.04 g/kg, IIICD >1.04 g/kg; 2) life-long diet time (LDT), i.e., cumulative years of life in which daily protein intake exceeded dietary recommendations: ILDT <15 years, IILDT 15-19 years, IIILDT >19 years.

RESULTS

GFR was decreased in 19 % of the patients. With increasing protein intake, GFR decreased significantly (ICD 111 ml/min; IICD 105 ml/min; IIICD 99 ml/min. ILDT 112 ml/min; IILDT 103 ml/min; IIILDT 99 ml/min). Proteinuria was detected in 31 %, microalbuminuria in 7 %, and hypercalciuria in 23 % of the patients. 23 % of the patients had arterial hypertension, and 41 % revealed a nocturnal non-dipping status.

CONCLUSIONS

In patients with PKU on a lifelong diet we could detect impaired renal function in 19 %, proteinuria in 31 %, and arterial hypertension in 23 %. Thus, chronic kidney disease may develop in PKU patients, and routine renal function tests should be performed during long-term follow-up.

Molecular epidemiology and BH4-responsiveness in patients with phenylalanine hydroxylase deficiency from Galicia region of Spain

Knowledge of hyperphenylalaninemia (HPA) mutational spectrum in a population allows in many cases an accurate prediction of the phenotype and tetrahydrobiopterin (BH4) responsiveness, thus selecting an adequate treatment. In this work, we have performed the molecular characterization of 105 HPA patients from Galicia, in the northwest region of Spain, evaluating their phenotype and BH4 response. The mutational spectrum analysis showed 47 distinct mutations in 89 families, 37 of them (78.7%) corresponding to missense mutations. Six mutations account for 47.2% of all the investigated alleles, each one with a frequency ≥ 5% (IVS10-11G>A, p.R261Q, p.V388M, p.R176L, p.E280K, p.A300S). The most prevalent HPA mutations in Galicia are the common Mediterranean mutation IVS10-11G>A and p.R261Q, with frequencies of 13.8% and 10.5%, respectively. One novel mutation (p.K361Q; c.1081A>C) was also reported. Although a good genotype-phenotype correlation is observed, there is no exact correlation for some genotypes involving mutations p.R261Q, p.I65T or IVS10-11G>A. Forty seven patients were monitored for post-challenge BH4, establishing genotype-based predictions of BH4-responsiveness in all of them. All phenylketonuric patients with 2 nonresponsive mutations were unresponsive to BH4 and patients with mutations previously associated with BH4 responsiveness in the two alleles had a clear positive response to the test, with the exception of 5 patients with mutations p.R261Q, p.I65T and p.R68S. Our study supports a similar degree of heterogeneity of the HPA mutation spectrum in Galicia compared to reported data from Southern Europe. Patients carrying null mutations in both alleles showed the highest degree of concordance with the most severe phenotypes. Genotype is a good predictor of BH4 response.

Diurnal variation of phenylalanine and tyrosine concentrations in adult patients with phenylketonuria: subcutaneous microdialysis is no adequate tool for the determination of amino acid concentrations

BACKGROUND

Metabolic control and dietary management of patients with phenylketonuria (PKU) are based on single blood samples obtained at variable intervals. Sampling conditions are often not well-specified and intermittent variation of phenylalanine concentrations between two measurements remains unknown. We determined phenylalanine and tyrosine concentrations in blood over 24 hours. Additionally, the impact of food intake and physical exercise on phenylalanine and tyrosine concentrations was examined. Subcutaneous microdialysis was evaluated as a tool for monitoring phenylalanine and tyrosine concentrations in PKU patients.

METHODS

Phenylalanine and tyrosine concentrations of eight adult patients with PKU were determined at 60 minute intervals in serum, dried blood and subcutaneous microdialysate and additionally every 30 minutes postprandially in subcutaneous microdialysate. During the study period of 24 hours individually tailored meals with defined phenylalanine and tyrosine contents were served at fixed times and 20 min bicycle-ergometry was performed.

RESULTS

Serum phenylalanine concentrations showed only minor variations while tyrosine concentrations varied significantly more over the 24-hour period. Food intake within the patients' individual diet had no consistent effect on the mean phenylalanine concentration but the tyrosine concentration increased up to 300% individually. Mean phenylalanine concentration remained stable after short-term bicycle-exercise whereas mean tyrosine concentration declined significantly. Phenylalanine and tyrosine concentrations in dried blood were significantly lower than serum concentrations. No close correlation has been found between serum and microdialysis fluid for phenylalanine and tyrosine concentrations.

CONCLUSIONS

Slight diurnal variation of phenylalanine concentrations in serum implicates that a single blood sample does reliably reflect the metabolic control in this group of adult patients. Phenylalanine concentrations determined by subcutaneous microdialysis do not correlate with the patients' phenylalanine concentrations in serum/blood.

Long-term outcomes of blood phenylalanine concentrations in children with classical phenylketonuria

We are reporting a retrospective review of blood phenylalanine (Phe) concentrations in 33 patients with classical phenylketonuria (PKU) born between 1991 and 2009 and continuously followed up in our clinic in 2009. As an indicator of blood Phe control, we analysed the percentage of blood Phe concentrations within and outside of the treatment range for each individual for treatment periods between 1 month and 12 months, 1 to 6 years, and 6 to 12 years of age. Despite early diagnosis and medical management in a centralized care model, only approximately 40% of patients had 60% and more of their blood Phe concentrations within the treatment range during their lifetime treatment periods. There was no statistical difference for the percentage of blood Phe concentrations within the treatment range, the mean Phe concentrations or the SD between the various treatment periods. We found a correlation between Phe tolerance and percentage of blood Phe concentrations within the treatment range. Patients born between 1991 and 1999 had poorer control than those born later. A frequent quality assurance audit is recommended to assess treatment outcomes in clinics providing care to children with PKU.

Quality of life among parents of children with phenylketonuria (PKU)

Background

Parents of children with chronic conditions are known to be at risk of impairment in their quality of life (QoL). Studies considering other chronic conditions proposed diverse factors to have an impact on the parent’s QoL. So far, there has been little research on parents who have a child with phenylketonuria (PKU). This study was designed to evaluate the parental quality of life (PQoL) of parents of children and adolescents who have PKU and identify possible predictors of PQoL.

Methods

In this cross-sectional study 89 parents completed self-report measures of PQoL, family stress, social support, and parental coping. To determine the impact of these potential predictors on PQoL, regression and mediation analyses were performed.

Results

Most parents coped well with their children’s metabolic disorder. Family stress (β = −0.42; p < 0.001) and perceived social support (β = 0.33; p = 0.001) were proven to be the most powerful predictors, accounting together for 45% of the variance of PQoL. Social support mediated the association between family stress and PQoL.

Conclusions

The current study indicates that parents of younger children are an especially vulnerable group. Members of health-care teams should be able to identify and empower vulnerable parents to seek and maintain social support.

Neurocognitive functioning in adults with phenylketonuria: results of a long term study

OBJECTIVES

A controlled long-term study was performed to assess the neurological and neuropsychological performance in adult patients with early-treated phenylketonuria (PKU).

METHODS

We investigated 57 patients with early-treated classical PKU aged 19 to 41 years (mean age 31 years) and 46 matched healthy controls, matched for age and socioeconomic status. Patients and controls were assessed for their intelligence quotient (IQ), and attention and information-processing abilities. Magnetic resonance imaging (MRI) of the brain was performed in all patients. Neuropsychological assessments and MRI were repeated at a five-year-follow-up.

RESULTS

In the five-year interval IQ, information processing and attention of patients and controls remained constant. At both assessment times the IQ scores were significantly lower in patients compared to controls. Older adult patients (>32 years) showed poorer information processing and attention at both assessment times compared to young adult patients (<32 years) and controls. IQ, information processing and attention showed no correlation to imaging results but were significantly correlated to blood phenylalanine (Phe) levels in patients' childhood and adolescence, and Phe levels had been higher in the adolescent years of older adult patients.

CONCLUSIONS

Cognitive performance in adult patients with early-treated PKU does not seem to be subject to deterioration observable in a five-year interval. Neuropsychological assessment in adults with PKU revealed neurocognitive impairment particularly in older adult patients. This seems to refer to an early relaxation of diet that was recommended when the older patients were adolescents. Results indicate a benefit of dietary control during adolescence in PKU.

Visual functions in phenylketonuria-evaluating the dopamine and long-chain polyunsaturated fatty acids depletion hypotheses

BACKGROUND

In phenylketonuria presymptomatic treatment following newborn screening prevents severe mental and physical impairment. The reasons for subtle impairments of cerebral functions despite early treatment remain unclear. We assessed a broad spectrum of visual functions in early-treated patients with phenylketonuria and evaluated two hypotheses-the dopamine and the long-chain polyunsaturated fatty acids (LCPUFAs) depletion hypotheses.

METHODS

Contrast sensitivity, colour vision, electroretinography, frequency doubling technology campimetry (FDT), and their relation with blood phenylalanine and docosahexaenoic acid levels were assessed in 36 patients with phenylketonuria and 18 age-matched healthy controls.

RESULTS

Contrast sensitivity was significantly lower and total error scores in colour vision significantly higher in patients than controls. Electroretinography results differed significantly between patients and controls. We found a trend for the effect of phenylalanine-levels on contrast sensitivity and a significant effect on colour vision/FDT results. Docosahexaenoic acid levels in erythrocytes were not associated with visual functions.

CONCLUSION

This is the first evaluation of visual functions in phenylketonuria using a comprehensive ophthalmological test battery. We found no evidence supporting the long-chain polyunsaturated fatty acids depletion hypothesis. However, the effect of phenylalanine-levels on visual functions suggests that imbalance between phenylalanine and tyrosine may affect retinal dopamine levels in phenylketonuria. This is supported by the similar patterns of visual functions in patients with phenylketonuria observed in our study and patients with Parkinson's disease.

Long-term treatment with tetrahydrobiopterin in phenylketonuria: treatment strategies and prediction of long-term responders

Tetrahydrobiopterin (BH4) responsive phenylketonuria has been described more than 10 years ago. However, criteria for the identification of long-term BH4 responsive patients are not yet established. 116 patients with phenylketonuria, aged 4-18 years, were screened for potential long-term BH4 responsiveness by at least two of the following criteria: positive neonatal BH4 loading test, putative BH4 responsive genotype, and/or milder phenotype. Patients had to be on permanent dietary treatment. 23 patients fulfilled these criteria and were tested for long-term BH4 responsiveness: 18/23 were long-term BH4 responsive, 5/23 were not. On long-term BH4 treatment over a period of 48 ± 27 months in a dose of 14.9 ± 3.3mg/kg/day phenylalanine tolerance was increased from 452 ± 201 mg/day to 1593 ± 647 mg/day, corresponding to a mean increase of 1141 ± 528 mg/day. Dietary phenylalanine intake was increased stepwise according to a clear defined protocol. In 8/18 patients, diet was completely liberalized; 10/18 patients still received phenylalanine-free amino acid formula with 0.63 ± 0.23 g/kg/day. The most predictive value for long-term BH4 responsiveness was the combination of pretreatment phenylalanine of < 1200 μmol/L, pretreatment phenylalanine/tyrosine ratio of <15, phenylalanine/tyrosine ratio of <15 on treatment, phenylalanine tolerance of >20mg/kg/day at age 3 years, positive neonatal BH4 loading, and at least one putative BH4 responsive mutation (p = 0.00024). Our data show that long-term BH4 responsiveness may be predicted already during neonatal period by determining maximum pretreatment phenylalanine and phenylalanine/tyrosine concentrations, neonatal BH4 loading and PAH genotype. A clear defined protocol is necessary to install long-term BH4 treatment.

The mechanism of BH4 -responsive hyperphenylalaninemia--as it occurs in the ENU1/2 genetic mouse model

The Pah(enu1/enu2) (ENU1/2) mouse is a heteroallelic orthologous model displaying blood phenylalanine (Phe) concentrations characteristic of mild hyperphenylalaninemia. ENU1/2 mice also have reduced liver phenylalanine hydroxylase (PAH) protein content (∼20% normal) and activity (∼2.5% normal). The mutant PAH protein is highly ubiquitinated, which is likely associated with its increased misfolding and instability. The administration of a single subcutaneous injection of l-Phe (1.1 mg l-Phe/g body weight) leads to an approximately twofold to threefold increase of blood Phe and phenylalanine/tyrosine (Phe/Tyr) ratio, and a 1.6-fold increase of both nonubiquitinated PAH protein content and PAH activity. It also results in elevated concentrations of liver 6R-l-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)), potentially through the influence of Phe on GTP cyclohydrolase I and its feedback regulatory protein. The increased BH(4) content seems to stabilize PAH. Supplementing ENU1/2 mice with BH(4) (50 mg/kg/day for 10 days) reduces the blood Phe/Tyr ratio within the mild hyperphenylalaninemic range; however, PAH content and activity were not elevated. It therefore appears that BH(4) supplementation of ENU1/2 mice increases Phe hydroxylation levels through a kinetic rather than a chaperone stabilizing effect. By boosting blood Phe concentrations, and by BH(4) supplementation, we have revealed novel insights into the processing and regulation of the ENU1/2-mutant PAH.

Commentary: What degree of hyperphenylalaninaemia requires treatment?

Despite some 50 years' experience in the treatment of phenylketonuria and numerous scientific publications on the subject there is no clear consensus as to what degree of hyperphenylalaninaemia will result in intellectual impairment. Studies of three main types, on untreated cases of moderate hyperphenylalaninaemia, on treated cases of phenylketonuria, and on the effects of current blood phenylalanine concentration on executive function, have lead to different conclusions. Overall, there appears to be a fairly strong case for limiting dietary treatment to individuals whose blood phenylalanine levels would otherwise exceed 600 μmol/L. This is now policy in some European countries but a formal large-scale study of long-term outcomes to validate the approach is urgently required.

Free asymmetric dimethylarginine (ADMA) is low in children and adolescents with classical phenylketonuria (PKU)

INTRODUCTION

Free asymmetric dimethylarginine (ADMA) is a competitive inhibitor of the nitric oxide synthases (NOS). Suppression of nitric oxide (NO) synthesis increases the risk of atherosclerosis. Nevertheless, in the condition of oxidative stress, NOS blockade by ADMA may exert protective effects. Protein metabolism is altered in patients with phenylketonuria (PKU) on dietary treatment and as shown recently, oxidative stress is high in PKU. Since free ADMA concentrations are determined by both protein metabolism and oxidative stress we hypothesized, that free ADMA levels may be elevated in PKU patients.

DESIGN

Sixteen patientswith PKU on dietary treatment (mean age 10.1 ± 5.2 yrs), and 91 healthy children (mean age 11.6 ± 3.7 yrs) participated in a cross sectional study.

RESULTS

ADMA, total homocysteine (tHcy) and blood glucose were lower and the L-arginine/ADMA ratio was higher in PKU patients compared to controls. No significant correlation was present between phenylalanine (Phe) concentrations, protein intake, and lipid profile, history of cardiovascular disease or ADMA.

DISCUSSION

In contrast to our hypothesis, ADMAwas lower and the L-arginine/ADMA ratio was higher in PKU patients. Therefore, in PKU patients, the regulating function of ADMA on NO synthesis is altered and may thus contribute to oxidative stress.

Food products made with glycomacropeptide, a low-phenylalanine whey protein, provide a new alternative to amino Acid-based medical foods for nutrition management of phenylketonuria

Phenylketonuria (PKU), an inborn error in phenylalanine metabolism, requires lifelong nutrition management with a low-phenylalanine diet, which includes a phenylalanine-free amino acid-based medical formula to provide the majority of an individual's protein needs. Compliance with this diet is often difficult for older children, adolescents, and adults with PKU. The whey protein glycomacropeptide (GMP) is ideally suited for the PKU diet because it is naturally low in phenylalanine. Nutritionally complete, acceptable medical foods and beverages can be made with GMP to increase the variety of protein sources for the PKU diet. As an intact protein, GMP improves protein use and increases satiety compared with amino acids. Thus, GMP provides a new, more physiologic source of low-phenylalanine dietary protein for people with PKU.

[Treatment and control of patients with phenylketonuria: results from the Collaborative Group of Spanish Follow-up Units]

BACKGROUND AND OBJECTIVE

To evaluate the management of phenylketonuria (PKU) in Spanish metabolic units and to develop a patients registry.

PATIENTS AND METHODS

PKU patients diagnosed and/or followed up in Spain, with phenylalanine values before treatment > 360 μmol/L. Registered anonymous data are those yielded by the units during 2010.

RESULTS

Data from the 18 Spanish Follow-up Units were collected. Eighty-three per cent of Units are multidisciplinary, all of them corresponding to control patients of all ages, with uniform management criteria. Data of 688 PKU patients were registered (median: 14 years [1 month-53 years], 41.5% are presently > 18-year-old. 71.8% patients came from neonatal screening; 15.8% have mild-PKU, 26% moderate-PKU and 51.5% classic-PKU. 78.6% patients are treated with protein-restricted diet, 9.3% with BH4 and free diet and 7.8% with BH4 and diet. Dietary control was good in 58.6% patients, intermediate in 26% and poor in 15.3%. Median (range) intellectual quotients was 97 (25-145). The number of neurological complications in late diagnosed patients was three-times higher than those of neonatal screening patients. 13.3% of adults had university studies and 37.5% had a stable couple.

CONCLUSIONS

This study allows for the first time the evaluation of the PKU management by Spanish PKU Follow-up Units, as well as the analysis and registry of controlled PKU patients. The study makes evident the need of adult Follow-up Units and the importance of neonatal screening for PKU patients prognosis.

Unrestricted consumption of fruits and vegetables in phenylketonuria: no major impact on metabolic control

BACKGROUND/OBJECTIVES

The treatment of phenylketonuria (PKU) requires consistent restriction of protein intake from natural sources. Therefore, protein from all foods has to be accounted for, even the small amounts in fruits and vegetables. We studied whether free consumption of fruits and vegetables containing less than 75 mg phenylalanine (phe) per 100 g affects metabolic control in children with PKU.

SUBJECTS/METHODS

Fourteen children (2-10 years) were included in a cross-over study, with a two-week period of conventional treatment (accounting for protein from fruits and vegetables) and a two-week period with free fruit and vegetable consumption. The instruction to follow liberal fruit and vegetable consumption in the first or second study period was randomized. Detailed daily dietary records were obtained throughout the study. Phe and nutrient content was calculated. Dried-blood phe concentration was monitored daily.

RESULTS

Although total phe intake increased by an average of 58 mg per day (P=0.037) during the 2 weeks of free fruit and vegetable consumption, dried-blood phe concentrations were unchanged. Total intake of fruits and vegetables did not increase, but patients instead used the higher phe tolerance to consume more of other foods, which were calculated and accounted for.

CONCLUSION

Free consumption of fruits and vegetables does not impair metabolic control in PKU patients over a 2-week period.

Chaperone-like therapy with tetrahydrobiopterin in clinical trials for phenylketonuria: is genotype a predictor of response?

Prospectively enrolled phenylketonuria patients (n=485) participated in an international Phase II clinical trial to identify the prevalence of a therapeutic response to daily doses of sapropterin dihydrochloride (sapropterin, KUVAN(®)). Responsive patients were then enrolled in two subsequent Phase III clinical trials to examine safety, ability to reduce blood Phenylalanine levels, dosage (5-20 mg/kg/day) and response, and bioavailability of sapropterin. We combined phenotypic findings in the Phase II and III clinical trials to classify study-related responsiveness associated with specific alleles and genotypes identified in the patients. We found that 17% of patients showed a response to sapropterin. The patients harbored 245 different genotypes derived from 122 different alleles, among which ten alleles were newly discovered. Only 16.3% of the genotypes clearly conferred a sapropterin-responsive phenotype. Among the different PAH alleles, only 5% conferred a responsive phenotype. The responsive alleles were largely but not solely missense mutations known to or likely to cause misfolding of the PAH subunit. However, the metabolic response was not robustly predictable from the PAH genotypes, based on the study design adopted for these clinical trials, and accordingly it seems prudent to test each person for this phenotype with a standardized protocol.

Phenylalanine hydroxylase deficiency

Phenylalanine hydroxylase deficiency is an autosomal recessive disorder that results in intolerance to the dietary intake of the essential amino acid phenylalanine. It occurs in approximately 1:15,000 individuals. Deficiency of this enzyme produces a spectrum of disorders including classic phenylketonuria, mild phenylketonuria, and mild hyperphenylalaninemia. Classic phenylketonuria is caused by a complete or near-complete deficiency of phenylalanine hydroxylase activity and without dietary restriction of phenylalanine most children will develop profound and irreversible intellectual disability. Mild phenylketonuria and mild hyperphenylalaninemia are associated with lower risk of impaired cognitive development in the absence of treatment. Phenylalanine hydroxylase deficiency can be diagnosed by newborn screening based on detection of the presence of hyperphenylalaninemia using the Guthrie microbial inhibition assay or other assays on a blood spot obtained from a heel prick. Since the introduction of newborn screening, the major neurologic consequences of hyperphenylalaninemia have been largely eradicated. Affected individuals can lead normal lives. However, recent data suggest that homeostasis is not fully restored with current therapy. Treated individuals have a higher incidence of neuropsychological problems. The mainstay of treatment for hyperphenylalaninemia involves a low-protein diet and use of a phenylalanine-free medical formula. This treatment must commence as soon as possible after birth and should continue for life. Regular monitoring of plasma phenylalanine and tyrosine concentrations is necessary. Targets of plasma phenylalanine of 120-360 μmol/L (2-6 mg/dL) in the first decade of life are essential for optimal outcome. Phenylalanine targets in adolescence and adulthood are less clear. A significant proportion of patients with phenylketonuria may benefit from adjuvant therapy with 6R-tetrahydrobiopterin stereoisomer. Special consideration must be given to adult women with hyperphenylalaninemia because of the teratogenic effects of phenylalanine. Women with phenylalanine hydroxylase deficiency considering pregnancy should follow special guidelines and assure adequate energy intake with the proper proportion of protein, fat, and carbohydrates to minimize risks to the developing fetus. Molecular genetic testing of the phenylalanine hydroxylase gene is available for genetic counseling purposes to determine carrier status of at-risk relatives and for prenatal testing.

Effect of tetrahydrobiopterin on Phe/Tyr ratios and variation in Phe levels in tetrahydrobiopterin responsive PKU patients

BACKGROUND

Whilst a reduction in blood phenylalanine (Phe) levels is essential in patients with PKU, a decrease in Phe/Tyrosine (Tyr) ratio and fluctuations in blood Phe levels over time have been recently associated with improved neuropsychological outcome. The aim of this study was to identify if Tetrahydrobiopterin (BH(4)) offers additional benefit based on the assumption that these 2 factors are beneficial.

METHOD

Since 2002, 9 patients identified through NBS as BH(4) responsive (BH(4) group) and 25 non-responsive patients (non-BH(4) group) produced a total of 1384 and 4415 samples, respectively, for analysis. Statistical analysis was performed to compare mean and median Phe levels, Tyr levels and Phe/Tyr ratios in BH(4) and non BH(4) responsive patients.

RESULTS

Variations in blood Phe levels were greater in the non-BH(4) group (BH(4): median 338 μmol/L, 95% Confidence Interval (CI) 329-346, mean: 358 μmol/L, CI 350-366; non-BH(4): median 338 μmol/L CI 332-344, mean: 370 μmol/L CI 364-376). Variations in blood Tyr levels were slightly greater in the non-BH(4) group: (BH(4): median 59 μmol/L CI 58-61, mean 67 CI 66-69; non-BH(4): median 62 μmol/L CI 61-63, mean 70 CI 69-71). The variation in Phe/Tyr ratios was greater in the non-BH(4) group (mean 6.12, CI 5.9-6.3) than in the BH(4) group (Mean 5.44, CI 5.3-5.6), particularly at blood Phe levels >600 μmol/L.

CONCLUSION

BH(4) responsive patients have smaller variations in blood Phe levels and tighter Phe/Tyr ratios than non-BH(4) responsive patients, particularly at high blood Phe levels. If decreased fluctuations in Phe levels and a decreased Phe/Tyr ratio are indeed neuro-protective, then BH(4) responsiveness is advantageous over diet alone in PKU. Neuropsychological testing in patients who have been treated with BH(4) long term may be able to ascertain the clinical benefit of these biochemical findings.

Correlation of age-specific phenylalanine levels with intellectual outcome in patients with phenylketonuria

Patients with treated phenylketonuria (PKU) can have subtle deficits in intellect, academic skills, and executive functioning. This study evaluates the relationship between intellectual outcome and concentration/variation in blood phenylalanine (Phe) during specific developmental periods (0-6 years, 7-12 years, >12 years) in our patients with PKU. Verbal comprehension, perceptual reasoning, and processing speed were used as measures of intelligence. Data were collected from 55 patients receiving treatment at the University of Utah Metabolic Clinic. Yearly median Phe levels increased and mean number of blood Phe samples decreased as patients aged. Yearly median blood Phe from 0-6 and 7-12 years were inversely associated with perceptual reasoning abilities using linear regression. Additionally, increased blood Phe concentration negatively impacted specific areas of verbal comprehension abilities for those 0-6 years of age (p = 0.001). Variation of Phe levels around the mean (assessed as standard deviation) in each patient was associated with diagnostic (highest pretreatment) Phe levels and yearly median Phe levels (p < 0.001 for both), but did not significantly impact intelligence in our group of patients. Frequent blood Phe monitoring from 7-12 years significantly reduced the probability of yearly median Phe exceeding 360 μM (p = 0.005). Our data show that compliance with treatment in patients with PKU affects both the concentration and variation of blood Phe levels, and may have a greater impact on verbal comprehension and perceptual reasoning skills during the first 12 years of life when compared the influence beyond 12 years.

Safety of extended treatment with sapropterin dihydrochloride in patients with phenylketonuria: results of a phase 3b study

BACKGROUND

Phenylketonuria (PKU) results from impaired breakdown of phenylalanine (Phe) due to deficient phenylalanine hydroxylase (PAH) activity. Sapropterin dihydrochloride (sapropterin, Kuvan®) is the only US- and EU-approved pharmaceutical version of naturally occurring 6R-BH(4), the cofactor required for PAH activity. Sapropterin enhances residual PAH activity in sapropterin-responsive PKU patients and, in conjunction with dietary management, helps reduce blood Phe concentrations for optimal control. Approval was based on the positive safety and efficacy results of four international clinical studies, the longest of which was 22 weeks in duration.

OBJECTIVE

To evaluate the safety of long-term treatment with sapropterin in PKU subjects who participated in previous Phase 3 sapropterin trials.

METHODS

PKU-008 was designed as a Phase 3b, multicenter, multinational, open-label, 3-year extension trial to evaluate the long-term safety of sapropterin in patients with PKU who were classified as sapropterin responders and participated in prior Phase 3 sapropterin studies: 111 subjects aged 4-50 years completed prior studies and were subsequently enrolled in study PKU-008. Routine safety monitoring was performed at 3-month intervals and included adverse event reporting, blood Phe monitoring, clinical laboratory evaluations, physical examinations and vital sign measurements.

RESULTS

Average exposure during PKU-008 was 658.7±221.3 days (range, 56-953; median, 595). The average total duration of participation in multiple studies (PKU-001, PKU-003, PKU-004, and PKU-008; or PKU-006 and PKU-008) was 799.0±237.5 days (range, 135-1151). The mean sapropterin dose was 16.2±4.7 mg/kg/day. Most adverse events were considered unrelated to treatment, were mild or moderate in severity, and were consistent with prior studies of sapropterin. No age-specific differences were observed in adverse event reporting. Three subjects discontinued treatment due to adverse events that were considered possibly or probably related to study treatment (one each of difficulty concentrating, decreased platelet count, and intermittent diarrhea). No deaths were reported. Of seven reported serious adverse events, one was considered possibly related to study treatment (gastroesophageal reflux). There were no laboratory or physical examination abnormalities requiring medical interventions. For most subjects, blood Phe concentrations were consistently within target range, confirming the durability of response in subjects undergoing extended treatment with sapropterin.

CONCLUSION

Sapropterin treatment was found to be safe and well tolerated at doses of 5 to 20mg/kg/day for an average exposure of 659 days. This study supports the safety and tolerability of sapropterin as long-term treatment for patients with PKU.

Follow up of phenylketonuria patients

In recent years our understanding of the follow up policies for PKU has increased substantially. In particular, we now understand the importance of maintaining control of blood phenylalanine (phe) concentrations life-long to achieve the best long-term neuropsychological outcomes. The concordance with the follow up strategy remains a key challenge for the future, especially with respect to adolescents and young adults. The recent therapies could ease the burden of the dietary phe restriction for PKU patients and their families. The time may be right for revisiting the guidelines for follow up of PKU in order to address a number of important issues related to PKU management: promotion of breastfeeding to complementary feeding up to 2 years of age for prevention of early growth retardation and later overweight development, treatment advancements for metabolic control, blood phe and tyr variability, routine screening measures for nutritional biomarkers, neurocognitive and psychological assessments, bone pathology, understanding the challenges of compliance and transitioning into adulthood as an individual with PKU and addressing unmet needs in this population.

Long-term follow-up of patients with phenylketonuria receiving tetrahydrobiopterin treatment

Treatment with tetrahydrobiopterin (BH4), the natural cofactor of phenylalanine hydroxylase (PAH), can reduce blood phenylalanine (Phe) levels in patients with BH4-responsive phenylketonuria (PKU). A number of studies has reported on the short-term BH4 treatment of patients with PKU, but long-term data are lacking. Here, we describe the effects of long-term treatment with BH4 on 16 patients, who showed a >28% reduction in blood Phe following testing for BH4 overload. The mean dose of BH4 was 16 mg/kg body weight (range 5-36 mg/kg body weight). The mean treatment duration was 56 months (range 24-110 months). Of 16 patients, 14 achieved long-term Phe control with BH4 treatment, with a mean blood Phe concentration of 321 ± 236 µmol/l. The mean decrease from baseline in blood Phe levels in these 14 patients was 54.6%. Of the seven patients who required continued dietary restriction, Phe intake increased from 200-300 mg/day to 800-1000 mg/day. Factors that may cause fluctuation of Phe levels in BH4-treated patients include patients' PAH genotype, Phe intake, changes in protein catabolism or anabolism, and periods of illness or infection.

Sapropterin dihydrochloride for phenylketonuria and tetrahydrobiopterin deficiency

Sapropterin dihydrochloride is the first registered synthetic form of the naturally occurring cofactor and cosubstrate, tetrahydrobiopterin (BH4). It is essential for the conversion of phenylalanine (Phe) by phenylalanine-4-hydroxylase (PAH) to tyrosine. BH4 is also the co-factor of rate-limiting enzymes involved in the synthesis of monoamine neurotransmitters. Phenylketonuria (PKU) is an inherited disorder of PAH, characterized by elevated Phe concentrations (hyperphenylalaninemia) in the blood and brain, with toxic neurological consequences. Sapropterin dihydrochloride is approved for treating patients (of all ages in the USA and >4 years old in Europe) with PKU who are BH4 responsive, and those with BH4 deficiency (Europe). It decreases blood Phe concentration and increases dietary Phe tolerance in some patients with PKU on a low-Phe diet, allowing dietary adjustment or even discontinuation of a low-Phe diet. This article reviews sapropterin dihydrochloride for the management of PKU - aimed at improving clinical outcomes and quality of life - and it considers the potential for incorporating such information into international consensus guidelines.