Phenylketonuria: dietary and therapeutic challenges

Genotype-Phenotype Correlation in a Large Cohort of Eastern Sicilian Patients Affected by Phenylketonuria: Newborn Screening Program, Clinical Features, and Follow-Up

Background: Phenylketonuria (PKU) is an autosomal recessive disorder caused by mutations in the phenylalanine hydroxylase (PAH) gene, leading to impaired amino acid metabolism. Early diagnosis through newborn screening (NBS) enables prompt treatment, preventing neurological complications. This study aims to describe the genetic and phenotypic spectrum of PKU and mild hyperphenylalaninemia (m-HPA) in patients diagnosed at the Department of Inborn Errors of Metabolism and Newborn Screening, Hospital G. Rodolico-S. Marco, Catania, over four decades (1987-2023). Materials and Methods: The retrospective analysis included 102 patients with elevated blood phenylalanine (Phe) levels born in Sicily and followed at the Institute. The phenotype evaluation comprised the Phe levels at birth/diagnosis, dietary tolerance, and sapropterin dihydrochloride responsiveness. The dietary compliance and Phe/Tyr ratios were assessed and compared across phenotypic classes and age groups. Results: Of 102 patients, 34 were classified as having classic PKU, 9 as having moderate PKU, 26 as having mild PKU, and 33 as having m-HPA, with a median age of 21.72 years. Common PAH variants included c.1066-11G>A (26/204 alleles), c.782G>A (18/204 alleles), and c.165delT (13/204 alleles). The phenotypes sometimes diverged from the genotype predictions, emphasizing dietary tolerance over the initial Phe levels for classification: m-HPA was statistically associated with a higher dietary tolerance (p < 0.001) compared to the classic, moderate, or mild forms of PKU. Conclusions: This study highlights the importance of large databases (e.g., BioPKU) for phenotype prediction and treatment optimization. Regular assessment of Phe/Tyr ratios is crucial for monitoring adherence and health. Phenotype determination, dietary management, and emerging therapies (Pegvaliase and gene therapy) are key to improving outcomes for PKU patients.

Exopolysaccharides of Lactic Acid Bacteria: Production, Purification and Health Benefits towards Functional Food

Lactic acid bacteria (LAB) are capable of synthesising metabolites known as exopolysaccharides (EPS) during fermentation. Traditionally, EPS plays an important role in fermented dairy products through their gelling and thickening properties, but they can also be beneficial to human health. This bioactivity has gained attention in applications for functional foods, which leads them to have prebiotic, immunomodulatory, antioxidant, anti-tumour, cholesterol-lowering and anti-obesity activity. Understanding the parameters and conditions is crucial to optimising the EPS yields from LAB for applications in the food industry. This review provides an overview of the functional food market together with the biosynthesis of EPS. Factors influencing the production of EPS as well as methods for isolation, characterisation and quantification are reviewed. Finally, the health benefits associated with EPS are discussed.

Nutrient intake, body composition, and blood phenylalanine control in children with phenylketonuria compared to healthy controls

Background

Phenylketonuria (PKU) treatment consists of life-long protein restriction and Phe-free medical foods for adequate nutritional intake and growth. A relationship between body composition and blood phenylalanine (Phe) concentrations in subjects with PKU has been proposed but this has not been consistently reported.

Methods

Dietary intake, lean body mass (LBM) and fat mass (FM) were measured in 30 pediatric subjects with PKU compared to 30 age, and sex matched controls. The relationship between body composition and blood Phe was analyzed within the PKU cohort from clinically collected dried blood spot Phe concentrations.

Results

Male subjects with PKU had less LBM% and more FM% than controls (p = .024). There was no difference in LBM% and FM% among female subjects. Age (p = .02) and FM% (p = .02) were positively correlated to dried blood spot Phe. Synthetic protein intake (g/kg body weight) was negatively correlated with dried blood spot Phe (p = .04). Natural protein intake was not related to blood spot Phe.

Conclusions

Children with PKU face additional dietary challenges maintaining healthy growth and body composition while keeping Phe levels low. We observed higher FM% and lower LBM% in male subjects with PKU. Correlations do not prove cause and effect but suggest a relationship between increased blood Phe, lower synthetic protein intake and increased FM%. Future studies may explore if lower blood Phe concentrations is associated with a lower FM% and higher LBM%; particularly among adult patients now managed on pegvaliase (Palynziq®) who consume normal amounts of natural protein or among younger patients who consume glycomacropeptide (GMP).

OVERWEIGHT AND ASSOCIATED FACTORS IN CHILDREN AND ADOLESCENTS WITH PHENYLKETONURIA: A SYSTEMATIC REVIEW

Objective:

To verify the occurrence of overweight in children and adolescents with phenylketonuria and to identify possible causal factors.

Data sources:

A systematic review was performed in the SciELO, PubMed and VHL databases using the descriptors “Phenylketonurias”, “Overweight”, “Child” and “Adolescent”. Original articles conducted with children and adolescents, published between 2008 and 2018 in Portuguese, English or Spanish languages were included.

Data synthesis:

A total of 16 articles were identified and, after screening procedures, 6 studies were selected for the review. Overweight in children and adolescents with phenylketonuria was a frequent occurence in the studies included in this review, ranging from 7.8 to 32.6%. The female sex was the most affected by the nutritional disorder. Furthermore, a high caloric intake combined with a lack of stimuli to practice physical activities were main factors associated with the excessive weight in the population of interest.

Conclusions:

Excess weight can be considered a common outcome in children and adolescents with phenylketonuria. It is mainly caused by inadequate food consumption and sedentary lifestyle. The importance of early identification of nutritional disturbances in children and adolescents with phenylketonuria should be emphasized, in order to prevent associated chronic diseases and to promote health by encouraging continued healthy eating habits and the regular practice of physical exercises.

Exploring Drivers of Liking of Low-Phenylalanine Products in Subjects with Phenyilketonuria Using Check-All-That-Apply Method

The aim of the present study was to apply the Check-all-that-apply (CATA) method in an ambulatory context involving subjects with phenylketonuria (PKU) to obtain a sensory description and to find the drivers of liking of low-phenylalanine products (Glycomacropeptide vs. L-amino acids formulas). 86 subjects with PKU (age range: 8–55 years) evaluated 8 samples: 4 L-amino acid formulas and 4 Glycomacropeptide (GMP) formulas, flavored with neutral, chocolate, strawberry and tomato aromas. Participants were asked to indicate which sensory attributes characterized each formulations and to score the overall liking. Significant differences were found regarding liking scores (F = 65.29; p < 0.001). GMP samples flavored with chocolate and strawberry, described as sweets, with a mild and natural taste and odor, were the most appreciated. Overall, GMP formulas obtained higher liking scores compared to L-amino acid formulas. Tomato flavored samples, described as bitter, salty, with artificial color, with strong taste and odor, obtained the lowest scores. In conclusion, CATA questionnaire seems to be a suitable method also in ambulatory context since this approach suggested that different foods and beverages with GMP could be developed to improve dietary treatment compliance of subjects with PKU from school age onwards.

Carbohydrate status in patients with phenylketonuria

BACKGROUND

In patients with phenylketonuria (PKU), a low-phenylalanine (Phe) diet supplemented with low-protein foods and a Phe-free amino acid mixture favors a dietary intake rich in carbohydrates, but little is known about how these molecules are metabolized in this setting. The objective of the present study was to analyze carbohydrate metabolism in patients with hyperphenylalaninemia.

METHODS

We conducted a multicenter cross-sectional study to investigate biochemical markers of basal and postprandial carbohydrate metabolism in PKU patients according to age, Phe tolerance, waist circumference and body mass index (BMI), diet, tetrahydrobiopterin (BH4) supplementation, and adherence to treatment. Basal biomarkers and anthropometric parameters were also evaluated in patients with mild hyperphenylalaninemia (MHPA) and in healthy controls.

RESULTS

A total of 83 patients aged 4-52 years were studied; 68.7% had PKU and 31.3% had MHPA. 68 healthy controls of similar sex and age were also evaluated Metabolic control was adequate in 71.9% of PKU patients. Fasting glucose levels (mean 80.77 ± 8.06 mg/dL) were high in just one patient, but fasting insulin levels, with a mean of 12.74 ± 8.4 mIU/L, were altered in 15 PKU patients (26.3%) and markedly higher than in patients with MPHA (p = 0.035). Fasting insulin levels and Homeostasis Model Assessment Insulin Resistance (HOMA-IR) were significantly higher than in healthy controls and correlated with body mass index, waist circumference, age, and also showed statistically significant differences according to diagnosis and Phe tolerance (p < 0.05). Patients under BH4 therapy had lower insulin levels and HOMA-IR. A higher mean carbohydrate intake from AA mixtures was observed in classic PKU patients. The caloric intake in the form of carbohydrates was also higher in PKU than MHPA patients (p = 0.038) and it was correlated with basal insulin (rho = 0.468, p = 0.006), HOMA-IR (rho = 0.423, p = 0.02), BMI (rho 0.533, p = 0.002), and waist circumference (rho 0.584, p = 0.0007).

CONCLUSIONS

This study shows that PKU patients are at risk of carbohydrate intolerance and insulin resistance, more evident in adults and overweight patients, probably related to their higher caloric intake in form carbohydrate content. A higher dependency of AA mixtures was demonstrated in PKU patients.

Arterial stiffness assessment in patients with phenylketonuria

In patients with phenylketonuria (PKU) compliant to diet greater tendency to overweight and higher inflammatory biomarkers levels than controls were reported. Although this could lead to atherogenesis, the elastic properties of large arteries in PKU patients have never been assessed. The aim of this study was to assess arterial stiffness measured by applanation tonometry in PKU patients compared to healthy controls.We carried out a cross-sectional study in 41 PKU patients (range age: 6-50 years old) and 41 age- and gender-matched healthy controls. Evaluated data included pharmacological treatment with sapropterin, clinical, and biochemical parameters. Aortic stiffness was assessed noninvasively by applanation tonometry measuring central blood pressure, aortic augmentation index (Aix@HR75), augmentation pressure (AP), and pulse wave velocity (PWV).We found higher PWV in classic PKU patients (6.60 m/second vs 5.26 m/second; P: .044). Percentage of PKU patients with PWV above 90 percentile was higher than controls (14.63% vs 2.32%; P: .048). A positive relationship was observed between the annual Phe median and PWV (r: 0.496; P: .012). PKU subjects with lower Phe tolerance showed more body weight (67.6 kg vs 56.8 kg; P: .012) and more PWV than those with higher Phe tolerance (6.55 m/second vs 5.42 m/second; P: .044).Our data show increased aortic stiffness in PKU patients, measured by applanation tonometry, when compared to healthy controls. Higher Phe levels are associated with a bigger PWV increase, which is not present in those subjects compliant to diet or under sapropterin treatment. These results could have marked effects in both research and clinical daily practice for a proper evaluation of cardiovascular risk in PKU subjects.

Evidence of Oxidative Stress and Secondary Mitochondrial Dysfunction in Metabolic and Non-Metabolic Disorders

Mitochondrial dysfunction and oxidative stress have been implicated in the pathogenesis of a number of diseases and conditions. Oxidative stress occurs once the antioxidant defenses of the body become overwhelmed and are no longer able to detoxify reactive oxygen species (ROS). The ROS can then go unchallenged and are able to cause oxidative damage to cellular lipids, DNA and proteins, which will eventually result in cellular and organ dysfunction. Although not always the primary cause of disease, mitochondrial dysfunction as a secondary consequence disease of pathophysiology can result in increased ROS generation together with an impairment in cellular energy status. Mitochondrial dysfunction may result from either free radical-induced oxidative damage or direct impairment by the toxic metabolites which accumulate in certain metabolic diseases. In view of the importance of cellular antioxidant status, a number of therapeutic strategies have been employed in disorders associated with oxidative stress with a view to neutralising the ROS and reactive nitrogen species implicated in disease pathophysiology. Although successful in some cases, these adjunct therapies have yet to be incorporated into the clinical management of patients. The purpose of this review is to highlight the emerging evidence of oxidative stress, secondary mitochondrial dysfunction and antioxidant treatment efficacy in metabolic and non-metabolic diseases in which there is a current interest in these parameters.

Lipid profile status and other related factors in patients with Hyperphenylalaninaemia

BACKGROUND

The mainstay of treating patients with phenylketonuria (PKU) is based on a Phe-restricted diet, restrictive in natural protein combined with Phe-free L-amino acid supplements and low protein foods. This PKU diet seems to reduce atherogenesis and confer protection against cardiovascular diseases but the results from the few published studies have been inconclusive. The aim of our study was to evaluate the relationship between the lipid profile and several treatment-related risk factors in patients with hyperphenylalaninaemia (HPA) in order to optimize their monitoring.

METHODS

We conducted a cross-sectional multicentre study. A total of 141 patients with HPA were classified according to age, phenotype, type of treatment and dietary adherence. Annual median blood phenylalanine (Phe) levels, Phe tolerance, anthropometric measurements, blood pressure (BP) and biochemical parameters [(triglycerides, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), apolipoprotein A (ApoA), apolipoprotein B (ApoB), vitamin B12, total homocysteine (tHcy), Methionine (Met), high sensitivity C-Reactive Protein (hsCRP)] were collected for each patient.

RESULTS

Plasma TC levels were lower in patients with PKU than in the mild-HPA group (150 ± 31 vs. 164 ± 22 mg/dL), and there was a weak inverse correlation between plasma TC and Phe levels. HDL-C, LDL-C, ApoA and ApoB levels were lower in the PKU group than in mild-HPA. Patients with PKU had higher systolic BP than the mild-HPA group and there was found a quadratic correlation between median Phe levels and systolic BP (p = 6.42e(-5)) and a linear correlation between median Phe levels and diastolic BP (p = 5.65e(-4)). In overweight or obese PKU patients (24.11 %), biochemical parameters such as TC, triglycerides, LDL-C, tHcy, hsCRP and BP were higher. By contrast, HDL-C was lower in these patients.

CONCLUSION

Our data show a direct correlation between lipid profile parameters and good adherence to the diet in PKU patients. However, lipid profile in overweight or obese patients displayed an atherogenic profile, in addition to higher hsCRP concentrations and BP. Our study contributes to a better understanding of the relationship between phenotype and treatment in patients with HPA, which could be useful in improving follow-up strategies and clinical outcome.

TRIAL REGISTRATION

Research Ethics Committee of Santiago-Lugo 2015/393. Registered 22 September 2015, retrospectively registered.

Diet in children with phenylketonuria and risk of cardiovascular disease: A narrative overview

AIMS

The aim of this paper is to review the possible relationship of restricted phenylalanine (Phe) diet, a diet primarily comprising low-protein foods and Phe-free protein substitutes, with major cardiovascular risk factors (overweight/obesity, blood lipid profile, plasma levels of homocysteine, adiponectin and free asymmetric dimethylarginine (ADMA), oxidative stress and blood pressure) in PKU children.

DATA SYNTHESIS

In PKU children compliant with diet, blood total cholesterol, low-density lipoprotein cholesterol (LDL-C), plasma ADMA levels and diastolic pressure were reported to be lower and plasma adiponectin levels to be higher compared to healthy controls. No difference was observed in overweight prevalence and in high-density lipoprotein cholesterol (HDL-C) levels. Inconsistent results were found for plasma homocysteine levels and antioxidant status.

CONCLUSIONS

PKU children compliant with diet seem to display non-different cardiovascular risks compared with the healthy population. Well-designed longitudinal studies are required to clarify the potential underlying mechanisms associated with PKU and cardiovascular risk factors.

New insights in growth of phenylketonuric patients

Treatment of phenylketonuria involves a restriction in the intake of natural proteins. This can lead to growth impairment. Weight, height and body mass index of 109 hyperphenylalaninemic patients (mild hyperphenylalaninemia (HPA) and phenylketonuria (PKU)) were determined from birth until 18 years, every 6 months, and differences to the healthy population, depending on the age, sex and phenotype, were analyzed. Data collection was longitudinal retrospective during 31 years. Statistical analysis of z-score values was performed by advanced statistical tools. Long-term evolution of anthropometric z-scores showed no significant statistical differences between PKU and mild HPA individuals, according to the general population. For PKU individuals, height is slightly lower and weight slightly higher than in the healthy population, but differences are smaller than one standard deviation. Nevertheless, over-time evolutions of female height z-scores are different in each type of pathology, with a crossover between 8 and 12 years (p = 0.0186).

CONCLUSIONS

It is nowadays possible to achieve a long-term normal growth in PKU patients with appropriate dietary treatment. There is however an acceleration of growth up to 8 years old for PKU female patients that leads to a slightly lower final height. Detection of this behaviour was possible by using nonlinear mixed effects models.

Sapropterin dihydrochloride for phenylketonuria

BACKGROUND

Phenylketonuria results from a deficiency of the enzyme phenylalanine hydroxylase. Dietary restriction of phenylalanine keeps blood phenylalanine concentration low. Most natural foods are excluded from diet and supplements are used to supply other nutrients. Recent publications report a decrease in blood phenylalanine concentration in some patients treated with sapropterin dihydrochloride. We examined the evidence for the use of sapropterin dihydrochloride to treat phenylketonuria. This is an update of a previously published Cochrane Review. 

OBJECTIVES

To assess the safety and efficacy of sapropterin dihydrochloride in lowering blood phenylalanine concentration in people with phenylketonuria.

SEARCH METHODS

We identified relevant trials from the Group's Inborn Errors of Metabolism Trials Register. Date of last search: 11 August 2014.We also searched ClinicalTrials.gov and Current controlled trials. Last search: 4 September 2014We contacted the manufacturers of the drug (BioMarin Pharmaceutical Inc.) for information regarding any unpublished trials.

SELECTION CRITERIA

Randomized controlled trials comparing sapropterin with no supplementation or placebo in people with phenylketonuria due to phenylalanine hydroxylase deficiency.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials and extracted outcome data.

MAIN RESULTS

Two placebo-controlled trials were included. One trial administered 10 mg/kg/day sapropterin in 89 children and adults with phenylketonuria whose diets were not restricted and who had previously responded to saproterin.This trial measured change in blood phenylalanine concentration. The second trial screened 90 children (4 to 12 years) with phenylketonuria whose diet was restricted, for responsiveness to sapropterin. Forty-six responders entered the placebo-controlled part of the trial and received 20 mg/kg/day sapropterin. This trial measured change in both phenylalanine concentration and protein tolerance. Both trials reported adverse events. The trials showed an overall low risk of bias; but both are Biomarin-sponsored. One trial showed a significant lowering in blood phenylalanine concentration in the sapropterin group (10 mg/kg/day), mean difference -238.80 μmol/L (95% confidence interval -343.09 to -134.51); a second trial (20 mg/kg/day sapropterin) showed a non-significant difference, mean difference -51.90 μmol/L (95% confidence interval -197.27 to 93.47). The second trial also reported a significant increase in phenylalanine tolerance, mean difference18.00 mg/kg/day (95% confidence interval 12.28 to 23.72) in the 20 mg/kg/day sapropterin group.

AUTHORS' CONCLUSIONS

There is evidence of short-term benefit from using sapropterin in some people with sapropterin-responsive forms of phenylketonuria; blood phenylalanine concentration is lowered and protein tolerance increased. There are no serious adverse events associated with using sapropterin in the short term.There is no evidence on the long-term effects of sapropterin and no clear evidence of effectiveness in severe phenylketonuria.

Phenylketonuria Scientific Review Conference: state of the science and future research needs

New developments in the treatment and management of phenylketonuria (PKU) as well as advances in molecular testing have emerged since the National Institutes of Health 2000 PKU Consensus Statement was released. An NIH State-of-the-Science Conference was convened in 2012 to address new findings, particularly the use of the medication sapropterin to treat some individuals with PKU, and to develop a research agenda. Prior to the 2012 conference, five working groups of experts and public members met over a 1-year period. The working groups addressed the following: long-term outcomes and management across the lifespan; PKU and pregnancy; diet control and management; pharmacologic interventions; and molecular testing, new technologies, and epidemiologic considerations. In a parallel and independent activity, an Evidence-based Practice Center supported by the Agency for Healthcare Research and Quality conducted a systematic review of adjuvant treatments for PKU; its conclusions were presented at the conference. The conference included the findings of the working groups, panel discussions from industry and international perspectives, and presentations on topics such as emerging treatments for PKU, transitioning to adult care, and the U.S. Food and Drug Administration regulatory perspective. Over 85 experts participated in the conference through information gathering and/or as presenters during the conference, and they reached several important conclusions. The most serious neurological impairments in PKU are preventable with current dietary treatment approaches. However, a variety of more subtle physical, cognitive, and behavioral consequences of even well-controlled PKU are now recognized. The best outcomes in maternal PKU occur when blood phenylalanine (Phe) concentrations are maintained between 120 and 360 μmol/L before and during pregnancy. The dietary management treatment goal for individuals with PKU is a blood Phe concentration between 120 and 360 μmol/L. The use of genotype information in the newborn period may yield valuable insights about the severity of the condition for infants diagnosed before maximal Phe levels are achieved. While emerging and established genotype-phenotype correlations may transform our understanding of PKU, establishing correlations with intellectual outcomes is more challenging. Regarding the use of sapropterin in PKU, there are significant gaps in predicting response to treatment; at least half of those with PKU will have either minimal or no response. A coordinated approach to PKU treatment improves long-term outcomes for those with PKU and facilitates the conduct of research to improve diagnosis and treatment. New drugs that are safe, efficacious, and impact a larger proportion of individuals with PKU are needed. However, it is imperative that treatment guidelines and the decision processes for determining access to treatments be tied to a solid evidence base with rigorous standards for robust and consistent data collection. The process that preceded the PKU State-of-the-Science Conference, the conference itself, and the identification of a research agenda have facilitated the development of clinical practice guidelines by professional organizations and serve as a model for other inborn errors of metabolism.

Dietary habits and metabolic control in adolescents and young adults with phenylketonuria: self-imposed protein restriction may be harmful

BACKGROUND

In untreated patients, phenylketonuria (PKU) results in severe encephalopathy with mental retardation. A protein-restricted diet is recommended which can be relaxed in adolescence/adulthood.

METHODS

We contacted all 72 adult/adolescent PKU patients who had been treated in our center during early childhood. Some still regularly attended our outpatient clinics, while others were lost for follow-up, giving 51 patients in our study. We asked all patients to complete a dietary protocol as well as a questionnaire on quality of life. Blood and urine were analyzed and body impedance plethysmography and cerebral MRI were performed.

RESULTS

42 % of the patients followed protein restriction supplemented with amino acid mixtures (AAM), others had a vegan diet with (8 %) or without (14 %) AAM; 36 % said they were eating normally and did not need any AAM. However, based on dietary protocols and blood urea levels, protein intake was restricted in this patient group. None of the patients examined had serious nutritional deficits. Phenylalanine levels were higher in patients not taking AAM. MRI of the brain was not different from those following protein restriction and taking AAM. The lesions score and mood correlated best with the cumulative phenylalanine values during the first 10 years of life.

CONCLUSION

In summary, 50 % of adult/adolescent patients from our center did not take AAM at the start of our survey although they unknowingly followed self-imposed protein restriction. They had no overt nutritional deficits; however, long-term brain function may be compromised. Our study emphasizes the need for specialized metabolic care in PKU during adulthood.

Estimating the probability of IQ impairment from blood phenylalanine for phenylketonuria patients: a hierarchical meta-analysis

Though the control of blood phenylalanine (Phe) levels is essential for minimizing impairment in individuals with phenylketonuria (PKU), the empirical basis for the selection of specific blood Phe levels as targets has not been evaluated. We evaluated the current evidence that particular Phe levels are optimal for minimizing or avoiding cognitive impairment in individuals with PKU. This work uses meta-estimates of blood Phe-IQ correlation to predict the probability of low IQ for a range of Phe levels. We believe this metric is easily interpretable by clinicians, and hence useful in making recommendations for Phe intake. The median baseline association of Phe with IQ was estimated to be negative, both in the context of historical (median = -0.026, 95 % BCI = [-0.040, -0.013]) and concurrent (-0.007, [-0.014, 0.000]) measurement of Phe relative to IQ. The estimated additive fixed effect of critical period Phe measurement was also nominally negative for historical measurement (-0.010, [-0.022, 0.003]) and positive for concurrent measurement (0.007, [-0.018, 0.035]). Probabilities corresponding to historical measures of blood Phe demonstrated an increasing chance of low IQ with increasing Phe, with a stronger association seen between blood Phe measured during the critical period than later. In contrast, concurrently-measured Phe was more weakly correlated with the probability of low IQ, though the correlation is still positive, irrespective of whether Phe was measured during the critical or non-critical period. This meta-analysis illustrates the utility of a Bayesian hierarchical approach for not only combining information from a set of candidate studies, but also for combining different types of data to estimate parameters of interest.

Breastfeeding follow-up in the treatment of children with phenylketonuria

Phenylketonuria (PKU) is the inability to convert phenylalanine into tyrosine, causing toxic effects to the central nervous system. Traditionally, in the treatment of PKU, breastfeeding is replaced by formula milk. This study verified the effects of breastfeeding as a source of phenylalanine on the development of children with PKU. Participants were ten infants with PKU who started treatment with the introduction of formula before 30 days of life, and maintained breastfeeding for at least 30 days after the start of procedures. The procedures were based on estimating breast milk intake, with a safe margin of phenylalanine concentration, calculating stomach volume, and initially offering formula, then breastfeeding on free demand, at every feeding. Breastfeeding duration ranged from one month and five days to 14 months. Blood controls were tested weekly. If the serum level of phenylalanine was >2 mg/dL and <6 mg/dL, the prescription was kept; if it was >2 mg/dL, the formula was decreased by 25%, indirectly increasing breastfeeding; if it was <6 mg/dL the formula was increased by 50%. The phenylalanine levels were assessed, and the Early Milestone Scale and the Basic Steps of Development were applied. Those who had normative index in all evaluations were considered adequate. Eighty percent of infants were able to keep safe concentrations of phenylalanine and development within normal indices. Continued breastfeeding is viable in the treatment of children with PKU, provided that phenylalanine levels are strictly controlled and the effects of breastfeeding on child development are monitored.

Evaluation of an adsorbent based on agricultural waste (corn cobs) for removal of tyrosine and phenylalanine from aqueous solutions

Adsorption of phenolic amino acids, such as phenylalanine and tyrosine, is quite relevant for the production of protein hydrolysates used as dietary formulations for patients suffering from congenital disorders of amino acid metabolism, such as phenylketonuria. In this study, an adsorbent prepared from corn cobs was evaluated for the removal of tyrosine (Tyr) from both a single component solution and a binary aqueous solution with phenylalanine (Phe). The adsorption behavior of tyrosine was similar to that of phenylalanine in single component solutions, however, with a much lower adsorption capacity (14 mg g⁻¹ for Tyr compared to 109 mg g⁻¹ for Phe). Tyr adsorption kinetics was satisfactorily described by a pseudosecond-order model as it was for Phe. In adsorption equilibrium studies for binary mixtures, the presence of Tyr in Phe solutions favored Phe faster adsorption whereas the opposite behavior was observed for the presence of Phe in Tyr solutions. Such results indicate that, in binary systems, Phe will be adsorbed preferably to Tyr, and this is a welcome feature when employing the prepared adsorbent for the removal of Phe from protein hydrolysates to be used in dietary formulations for phenylketonuria treatment.

Hyperphenylalaninemia in the Czech Republic: genotype-phenotype correlations and in silico analysis of novel missense mutations

BACKGROUND

Hyperphenylalaninemia (HPA) is one of the most common inherited metabolic disorders caused by deficiency of the enzyme phenylalanine hydroxylase (PAH). HPA is associated with mutations in the PAH gene, which leads to reduced protein stability and/or impaired catalytic function. Currently, almost 700 different disease-causing mutations have been described. The impact of mutations on enzyme activity varies ranging from classical PKU, mild PKU, to non-PKU HPA phenotype.

METHODS

We provide results of molecular genetic diagnostics of 665 Czech unrelated HPA patients, structural analysis of missense mutations associated with classical PKU and non-PKU HPA phenotype, and prediction of effects of 6 newly discovered HPA missense mutations using bioinformatic approaches and Molecular Dynamics simulations.

RESULTS

Ninety-eight different types of mutations were indentified. Thirteen of these were novel (6 missense, 2 nonsense, 1 splicing, and 4 small gene rearrangements). Structural analysis revealed that classical PKU mutations are more non-conservative compared to non-PKU HPA mutations and that specific sequence and structural characteristics of a mutation might be critical when distinguishing between non-PKU HPA and classical PKU mutations. The greatest impact was predicted for the p.(Phe263Ser) mutation while other novel mutations p.(Asn167Tyr), p.(Thr200Asn), p.(Asp229Gly), p.(Leu358Phe), and p.(Ile406Met) were found to be less deleterious.

Sapropterin dihydrochloride for phenylketonuria

BACKGROUND

Phenylketonuria results from a deficiency of the enzyme phenylalanine hydroxylase. Dietary restriction of phenylalanine keeps blood phenylalanine concentration low. Most natural foods are excluded from diet and supplements are used to supply other nutrients. Recent publications report a decrease in blood phenylalanine concentration in some patients treated with sapropterin dihydrochloride. We examined the evidence for the use of sapropterin dihydrochloride to treat phenylketonuria.  

OBJECTIVES

To assess the safety and efficacy of sapropterin dihydrochloride in lowering blood phenylalanine concentration in people with phenylketonuria.

SEARCH METHODS

We identified relevant trials from the Group's Inborn Errors of Metabolism Trials Register. Date of last search: 29 June 2012.We also searched ClinicalTrials.gov and Current controlled trials. Last search: 23 July 2012.We contacted the manufacturers of the drug (BioMarin Pharmaceutical Inc.) for information regarding any unpublished trials.

SELECTION CRITERIA

Randomized controlled trials comparing sapropterin with no supplementation or placebo in people with phenylketonuria due to phenylalanine hydroxylase deficiency.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials and extracted outcome data.

MAIN RESULTS

Two placebo-controlled trials were included. One trial administered 10 mg/kg/day sapropterin in 89 children and adults with phenylketonuria whose diets were not restricted and who had previously responded to saproterin.This trial measured change in blood phenylalanine concentration. The second trial screened 90 children (4 to 12 years) with phenylketonuria whose diet was restricted, for responsiveness to sapropterin. Forty-six responders entered the placebo-controlled part of the trial and received 20 mg/kg/day sapropterin. This trial measured change in both phenylalanine concentration and protein tolerance. Both trials reported adverse events. The trials showed an overall low risk of bias; but both are Biomarin-sponsored. One trial showed a significant lowering in blood phenylalanine concentration in the sapropterin group (10 mg/kg/day), mean difference -238.80 μmol/L (95% confidence interval -343.09 to -134.51); a second trial (20 mg/kg/day sapropterin) showed a non-significant difference, mean difference -51.90 μmol/L (95% confidence interval -197.27 to 93.47). The second trial also reported a significant increase in phenylalanine tolerance, mean difference18.00 mg/kg/day (95% confidence interval 12.28 to 23.72) in the 20 mg/kg/day sapropterin group.

AUTHORS' CONCLUSIONS

There is evidence of short-term benefit from using sapropterin in some patients with sapropterin-responsive forms of phenylketonuria; blood phenylalanine concentration is lowered and protein tolerance increased. There are no serious adverse events associated with using sapropterin in the short term.There is no evidence on the long-term effects of sapropterin and no clear evidence of effectiveness in severe phenylketonuria.

In vivo catecholaminergic metabolism in the medial prefrontal cortex of ENU2 mice: an investigation of the cortical dopamine deficit in phenylketonuria

OBJECTIVE

Phenylketonuria (PKU) is an inherited metabolic disease characterized by plasma hyperphenylalaninemia and several neurological symptoms that can be controlled by rigorous dietetic treatment. The cellular mechanisms underlying impaired brain functions are still unclear. It has been proposed, however, that phenylalanine interference in cognitive functions depends on impaired dopamine (DA) transmission in the prefrontal cortical area due to reduced availability of the precursor tyrosine. Here, using Pah(enu2) (ENU2) mice, the genetic murine model of PKU, we investigated all metabolic steps of catecholamine neurotransmission within the medial preFrontal Cortex (mpFC), availability of the precursor tyrosine, synthesis and release, to find an easy way to reinstate normal cortical DA neurotransmission.

METHODS AND RESULTS

Analysis of blood and brain levels of tyrosine showed reduced plasma and cerebral levels of tyrosine in ENU2 mice. Western blot analysis demonstrated deficient tyrosine hydroxylase (TH) protein levels in mpFC of ENU2 mice. Cortical TH activity, determined in vivo by measuring the accumulation of l-3,4-dihydroxyphenylalanine (L-DOPA) in mpFC after inhibition of L-aromatic acid decarboxylase with NSD-1015, was reduced in ENU2 mice. Finally, a very low dose of L-DOPA, which bypasses the phenylalanine-inhibited metabolic steps, restored DA prefrontal transmission to levels found in healthy mice.

CONCLUSION

The data suggests that a strategy of using tyrosine supplementation to treat PKU is unlikely to be effective, whereas small dose L-DOPA administration is likely to have a positive therapeutic effect.

A Systematic Review of BH4 (Sapropterin) for the Adjuvant Treatment of Phenylketonuria

CONTEXT

Dietary management is the mainstay of effective treatment in PKU, but dietary restriction is difficult and additional treatment options are needed.

OBJECTIVE

To systematically review evidence regarding sapropterin (BH4) use as an adjunct to dietary restriction in individuals with PKU.

DATA SOURCES

Five databases including MEDLINE up to August 2011.

STUDY SELECTION

Two reviewers independently assessed studies against predetermined inclusion/exclusion criteria.

DATA EXTRACTION

Two reviewers independently extracted data regarding participant and intervention characteristics and outcomes and assigned overall quality and strength of evidence ratings based on predetermined criteria.

RESULTS

BH4 research includes two randomized controlled trials (RCTs) and three uncontrolled open-label trials. Phenylalanine (Phe) levels were reduced by at least 30 % in up to half of treated participants (32-50 %). In one RCT comparing placebo on likelihood of a 30 % reduction in Phe, 9 % of those on placebo achieved this effect, compared with 44 % of the treated group after 6 weeks. Phe tolerance and variability were improved in treated participants in studies assessing those outcomes. No comparative studies assessed long-term outcomes including cognitive effects, nutritional status, or quality of life.

CONCLUSIONS

Adjuvant pharmacologic therapy has the potential to support individuals in achieving optimal Phe levels. BH4 has been shown to reduce Phe levels in some individuals, with significantly greater reductions seen in treated versus placebo groups. The strength of the evidence is moderate for short-term effects on reducing Phe in a subset of initially BH4-responsive individuals, moderate for a lack of significant harms, low for longer-term effects on cognition, and insufficient for all other outcomes.

[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.

Physical development in patients with phenylketonuria on dietary treatment: a retrospective study

OBJECTIVES

To evaluate the growth and physical development in patients with phenylalanine hydroxylase deficiency who follow exclusively dietary treatment.

METHODS

Anthropometric measurements of 160 patients with hyperphenylalaninemia who were followed at our center over a 25 year period were obtained. Only patients treated exclusively with a protein-restrictive diet supplemented with amino acid mixtures were included. Height, weight and body mass index were measured at birth, at diagnosis, at 6 and 12 months of age, and annually until 18 years of age in patients with phenylketonuria or until 9 years of age in patients with mild hyperphenylalaninemia and compared to official national reference values. The final height of PKU patients was also compared to their expected family height.

RESULTS

The analysis of z scores suggested no significant differences in physical development between PKU patients and the healthy population during the study period. The final height of PKU patients revealed that they were 2 to 4 cm taller than expected when compared to the mean family height (p<0.001). The mean weight and BMI at puberty suggested that many patients with severe PKU, but not other phenotypes, were overweight during this period.

CONCLUSION

Physical development can be optimal in PKU patients regardless of their phenotype and the severity of the diet. A tendency to excessive weight gain is seen in adolescence in the most severe phenotypes.

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.

Natural phenylalanine hydroxylase variants that confer a mild phenotype affect the enzyme's conformational stability and oligomerization equilibrium

Hyperphenylalaninemias are genetic diseases prevalently caused by mutations in the phenylalanine hydroxylase (PAH) gene. The wild-type PAH enzyme is a homotetramer regulated by its substrate, cofactor and phosphorylation. We reproduced a full-length wild-type protein and seven natural full-length PAH variants, p.I65M, p.N223Y, p.R297L, p.F382L, p.K398N, p.A403V, and p.Q419R, and analyzed their biochemical and biophysical behavior. All mutants exhibited reduced enzymatic activity, namely from 38% to 69% of wild-type activity. Biophysical characterization was performed by size-exclusion chromatography, light scattering and circular dichroism. In the purified wild-type PAH, we identified the monomer in equilibrium with the dimer and tetramer. In most mutants, the equilibrium shifted toward the dimer and most tended to form aggregates. All PAH variants displayed different biophysical behaviors due to loss of secondary structure and thermal destabilization. Specifically, p.F382L was highly unstable at physiological temperature. Moreover, using confocal microscopy with the number and brightness technique, we studied the effect of BH4 addition directly in living human cells expressing wild-type PAH or p.A403V, a mild mutant associated with BH4 responsiveness in vivo. Our results demonstrate that BH4 addition promotes re-establishment of the oligomerization equilibrium, thus indicating that the dimer-to-tetramer shift in pA403V plays a key role in BH4 responsiveness. In conclusion, we show that the oligomerization process and conformational stability are altered by mutations that could affect the physiological behavior of the enzyme. This endorses the hypothesis that oligomerization and folding defects of PAH variants are the most common causes of HPAs, particularly as regards mild human phenotypes.

Oxidative stress in phenylketonuria: what is the evidence?

Phenylketonuria (PKU) is an inborn error of amino acid metabolism caused by severe deficiency of phenylalanine hydroxylase activity, leading to the accumulation of phenylalanine and its metabolites in blood and tissues of affected patients. Phenylketonuric patients present as the major clinical feature mental retardation, whose pathomechanisms are poorly understood. In recent years, mounting evidence has emerged indicating that oxidative stress is possibly involved in the pathology of PKU. This article addresses some of the recent developments obtained from animal studies and from phenylketonuric patients indicating that oxidative stress may represent an important element in the pathophysiology of PKU. Several studies have shown that enzymatic and non-enzymatic antioxidant defenses are decreased in plasma and erythrocytes of PKU patients, which may be due to an increased free radical generation or secondary to the deprivation of micronutrients which are essential for these defenses. Indeed, markers of lipid, protein, and DNA oxidative damage have been reported in PKU patients, implying that reactive species production is increased in this disorder. A considerable set of data from in vitro and in vivo animal studies have shown that phenylalanine and/or its metabolites elicit reactive species in brain rodent. These findings point to a disruption of pro-oxidant/antioxidant balance in PKU. Considering that the brain is particularly vulnerable to oxidative attack, it is presumed that the administration of appropriate antioxidants as adjuvant agents, in addition to the usual treatment based on restricted diets or supplementation of tetrahydrobiopterin, may represent another step in the prevention of the neurological damage in PKU.

Communicative and psycholinguistic abilities in children with phenylketonuria and congenital hypothyroidism

The Neonatal Screening for Inborn Errors of Metabolism of the Association of Parents and Friends of Special Needs Individuals (APAE) - Bauru, Brazil, was implanted and accredited by the Brazilian Ministry of Health in 1998. It covers about 286 cities of the Bauru region and 420 collection spots. Their activities include screening, diagnosis, treatment and assistance to congenital hypothyroidism (CH) and phenylketonuria (PKU), among others. In 2005, a partnership was established with the Department of Speech-Language Pathology and Audiology, Bauru School of Dentistry, University of São Paulo, Bauru, seeking to characterize and to follow, by means of research studies, the development of the communicative abilities of children with CH and PKU. Objective: The aim of this study was to describe communicative and psycholinguistic abilities in children with CH and PKU. Materials and Methods: Sixty-eight children (25 children aged 1 to 120 months with PKU and 43 children aged 1 to 60 months with CH) participated in the study. The handbooks were analyzed and different instruments were applied (Observation of Communication Behavior, Early Language Milestone Scale, Peabody Picture Vocabulary Test, Gesell & Amatruda's Behavioral Development Scale, Portage Operation Inventory, Language Development Evaluation Scale, Denver Developmental Screening Test, ABFW Child Language Test-phonology and Illinois Test of Psycholinguistic Abilities), according to the children's age group and developmental level. Results: It was observed that the children with PKU and CH at risk for alterations in their developmental abilities (motor, cognitive, linguistic, adaptive and personal-social), mainly in the first years of life. Alterations in the psycholinguistic abilities were also found, mainly after the preschool age. Attention deficits, language and cognitive alterations were more often observed in children with CH, while attention deficits with hyperactivity and alterations in the personal-social, language and motor adaptive abilities were more frequent in children with PKU. Conclusion: CH and PKU can cause communicative and psycholinguistic alterations that compromise the communication and affect the social integration and learning of these individuals, proving the need of having these abilities assisted by a speech and language pathologist.

5-Hydroxytryptophan during critical postnatal period improves cognitive performances and promotes dendritic spine maturation in genetic mouse model of phenylketonuria

Although phenylketonuria (PKU) is the most common genetic cause of mental retardation, the cellular mechanisms underlying impaired brain function are still unclear. Using PAHenu2 mice (ENU2), the genetic mouse model of PKU, we previously demonstrated that high phenylalanine levels interfere with brain tryptophan hydroxylase activity by reducing the availability of serotonin (5-hydroxytryptamine, 5-HT), crucial for maturation of neuronal connectivity in the prefrontal cortex (PFC), around the third postnatal week, a critical period for cortical maturation. 5-Hydroxytryptophan (5-HTP), the product of tryptophan hydroxylation, is known to be a better treatment to increase brain 5-HT levels. In this study we investigated the role of 5-HT during the early postnatal period in cognitive disturbances and in cortical dendritic alterations of PKU subjects by restoring temporarily (postnatal days 14-21) physiological brain levels of 5-HT in ENU2 through 5-HTP treatment. In adult ENU2 mice early 5-HTP treatment reverses cognitive deficits in spatial and object recognition tests accompanied by an increase in spine maturation of pyramidal neurons in layer V of the prelimbic/infralimbic area of the PFC, although locomotor deficits are not recovered by treatment. Taken together, our results support the hypothesis that mental retardation in PKU depends on reduced availability of brain 5-HT during critical developmental periods that interferes with cortical maturation and point to 5-HTP supplementation as a highly promising additional tool to heal PKU patients.

Neurological complications and behavioral problems in patients with phenylketonuria in a follow-up unit

OBJECTIVE

To investigate the relationship between neurological complications, neuroradiological findings, and behavioral problems, age at diagnosis and dietary control along the follow-up of the PKU patients in our metabolic unit.

DESIGN

Retrospective study of the PKU patients diagnosed and controlled in our unit from 1985 to 2010.

METHODS

Registry of patients in a database with 50 items filled in by review of the clinical histories. Statistical study of the data (SPSS, 19.0 version).

RESULTS

121 patients were included (median age: 16.0, range 1 month-46 years). 76% of them were diagnosed through neonatal screening. 12.4% had mild-PKU, 19% moderate-PKU and 68.6% classic-PKU. 88.4% of patients were treated with a protein-restricted diet, and 11.6% with BH4. 97.7% of the early diagnosed patients had normal IQ, while 46.3% of late diagnosed patients had mental retardation, 28.5% were borderline and 25% had normal IQ. In early diagnosed patients, there was a significantly negative correlation between IQ [mean (SD) 100 (11.1)] and the index of dietary control during the first six years of life [median (range) 310 (105-992)] and that of the immediately past year [348 (106-1127)] (p < 0.0001). The proportion of patients with late diagnosis and neurological and behavioral problems was significantly higher than that of the early diagnosed ones (p < 0.001). The proportion of early diagnosed patients with neurological and behavioral problems who had good, intermediate or poor dietary control during the first 6 years of life and the immediately past year was significantly different (p < 0.001).

CONCLUSIONS

The results show the impact of early diagnosis and good dietary treatment on the IQ and on the percentage of neurological complications and behavioral problems in PKU patients.

Large neutral amino acids in daily practice

At the Kennedy Centre for Phenylketonuria, Denmark, large neutral amino acids (LNAAs) are being used to treat adult and adolescent patients who are nonadherent to dietary treatment for phenylketonuria (PKU). At the start of treatment, a patient must undergo dietary analysis and regular blood sampling to measure plasma amino acid (AA) concentrations. The aim of this analysis and treatment is that the patient receives 25-30% of the daily protein requirement from LNAA supplementation and the remaining 70-75% from natural, low-phenylalanine proteins (although some patients have difficulties in maintaining this level of protein intake). Patients are therefore able to follow a more "normal" diet than those adhering to a PKU diet with AA supplementation (in which only 20% of the daily protein requirement is provided from the diet and 80% from AA supplementation). LNAAs have also been used to treat older patients with untreated/late-diagnosed PKU who show profound intellectual, psychological, and behavioral impairments. Treatment with LNAAs has been shown to improve measures of concentration and awareness of external stimuli in some of these patients and thus enhance their socialization, emotionality, frustration tolerance, and mood.

Challenges and pitfalls in the management of phenylketonuria

Despite recent advances in the management of phenylketonuria and hyperphenylalaninemia, important questions on the management of this disorder remain unanswered. Consensus exists on the need for neonatal screening and early treatment, yet disagreement persists over threshold levels of blood phenylalanine for starting treatment, target blood phenylalanine levels, and the management of older patient groups. The mainstay of treatment is a phenylalanine-restricted diet, but its application varies between and within countries. Beyond diet treatment, there is a lack of consensus on the use of newer treatments such as tetrahydrobiopterin. Although neonatal screening and early treatment has meant that most well-treated children grow up with near-normal IQ scores, the effect of relaxing metabolic control on cognitive and executive function later in life is still not fully understood. Although it is clear from the available literature that the active control of blood phenylalanine levels is of vital importance, there are other treatment-related factors that affect outcome. A uniform and firmly evidence-based approach to the management of phenylketonuria is required.

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.

Sapropterin dihydrochloride for phenylketonuria

BACKGROUND

Phenylketonuria results from a deficiency of the enzyme phenylalanine hydroxylase. Dietary restriction of phenylalanine keeps blood phenylalanine concentration low. Most natural foods are excluded from diet and supplements are used to supply other nutrients. Recent publications report a decrease in blood phenylalanine concentration in some patients treated with sapropterin dihydrochloride. We examined the evidence for the use of sapropterin dihydrochloride to treat phenylketonuria.

OBJECTIVES

To assess the safety and efficacy of sapropterin dihydrochloride in lowering blood phenylalanine concentration in people with phenylketonuria.

SEARCH STRATEGY

We identified relevant trials from the Group's Inborn Errors of Metabolism Trials Register. Last search:07 May 2010.We also searched ClinicalTrials.gov and Current controlled trials. Last search: 01 September 2009.We contacted the manufacturers of the drug (BioMarin Pharmaceutical Inc.) for information regarding any unpublished trials.

SELECTION CRITERIA

Randomized controlled trials comparing sapropterin with no supplementation or placebo in people with phenylketonuria due to phenylalanine hydroxylase deficiency.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials and extracted outcome data.

MAIN RESULTS

Two placebo-controlled trials were included. One trial administered 10 mg/kg/day sapropterin in 89 children and adults with phenylketonuria whose diets were not restricted and who had previously responded to saproterin.This trial measured change in blood phenylalanine concentration. The second trial screened 90 children (4 to 12 years) with phenylketonuria whose diet was restricted, for responsiveness to sapropterin. Forty-six responders entered the placebo-controlled part of the trial and received 20 mg/kg/day sapropterin. This trial measured change in both phenylalanine concentration and protein tolerance. Both trials reported adverse events. The trials showed an overall low risk of bias; but both are Biomarin-sponsored. One trial showed a significant lowering in blood phenylalanine concentration in the sapropterin group (10 mg/kg/day), mean difference -238.80 mumol/L (95% confidence interval -343.09 to -134.51); a second trial (20 mg/kg/day sapropterin) showed a non-significant difference, mean difference -51.90 mumol/L (95% confidence interval -197.27 to 93.47). The second trial also reported a significant increase in phenylalanine tolerance, mean difference18.00 mg/kg/day (95% confidence interval 12.28 to 23.72) in the 20 mg/kg/day sapropterin group.

AUTHORS' CONCLUSIONS

There is evidence of short-term benefit from using sapropterin in some patients with sapropterin-responsive forms of phenylketonuria; blood phenylalanine concentration is lowered and protein tolerance increased. There are no serious adverse events associated with using sapropterin in the short term.There is no evidence on the long-term effects of sapropterin and no clear evidence of effectiveness in severe phenylketonuria.

Long-chain polyunsaturated fatty acid status in phenylketonuric patients treated with tetrahydrobiopterin

OBJECTIVES

To evaluate LCPUFA composition in PKU patients treated with BH(4).

DESIGN AND METHODS

Cross-sectional study of plasma and erythrocyte LCPUFA composition of 13 PKU patients treated with BH(4) compared with data from 48 PKU patients on protein-restricted diet, and 17 mild HPA patients on free diet. PUFA were analysed by gas chromatography.

RESULTS

Plasma and erythrocyte docosahexaenoic acid (DHA), and LCPUFA deficiency markers did not show significant differences in PKU patients on BH(4) compared with those with mild HPA and our reference values, but they did in comparison with PKU on protein-restricted diet (p<0.0001). Essential fatty acids and arachidonic acid composition were not significantly different in any of the studied groups. DHA values correlate with the index of dietary control only in PKU patients on protein-restricted diet (p=0.002).

CONCLUSION

LCPUFA status is within the reference values in PKU patients treated with BH(4). This translates to a further advantage of BH(4) therapy.

Undiagnosed maternal phenylketonuria: own clinical experience and literature review

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine (Phe) metabolism resulting from deficiency of phenylalanine hydroxylase (PAH). Most forms of PKU are caused by mutations in the PAH gene. Untreated PKU is associated with an abnormal phenotype, which includes growth failure, seizures, global developmental delay and severe intellectual impairment. The maternal PKU (MPKU) syndrome is caused by high blood Phe concentrations during pregnancy and presents with serious foetal anomalies, especially microcephaly, congenital heart disease and mental retardation. However, since the introduction of newborn screening programs and with early dietary intervention, children born with PKU can now expect to lead relatively normal lives. We present the case of a 33-year-old woman who had been diagnosed as having PKU only after a pregnancy with MPKU embryopathy, to emphasize that undiagnosed maternal phenylketonuria still exists. On that ground, we reviewed updated literature on the pathogenesis of this syndrome, possibility of prophylaxis and treatment.

Changes in kinetics of amino acid uptake at the ageing ovine blood-cerebrospinal fluid barrier

Amino acids (AA) in brain are precisely controlled by blood-brain barriers, which undergo a host of changes in both morphology and function during ageing. The effect of these age-related changes on AA homeostasis in brain is not well described. This study investigated the kinetics of four AA (Leu, Phe, Ala and Lys) uptakes at young and old ovine choroid plexus (CP), the blood-cerebrospinal fluid (CSF) barrier (BCB), and measured AA concentrations in CSF and plasma samples. In old sheep, the weight of lateral CP increased, so did the ratio of CP/brain. The expansion of the CP is consistent with clinical observation of thicker leptomeninges in old age. AA concentrations in old CSF, plasma and their ratio were different from the young. Both V(max) and K(m) of Phe and Lys were significant higher compared to the young, indicating higher trans-stimulation in old BCB. Cross-competition and kinetic inhibition studies found the sensitivity and specificity of these transporters were impaired in old BCB. These changes may be the first signs of a compromised barrier system in ageing brain leading increased AA influx into the brain causing neurotoxicity.

Dietary management practices in phenylketonuria across European centres

BACKGROUND

Dietary phenylalanine restriction is the cornerstone of phenylketonuria (PKU) management. However, there are no European consensus guidelines for its optimal dietary care.

METHODS

Detailed information on the routine dietary management of PKU was obtained from 10 European centres using structured questionnaires. Each centre was represented by one dietitian/nutritionist or physician (European Nutritionist Expert Panel).

RESULTS

All centres screened for PKU within the first 10 days of life. PKU prevalence was highest in Turkey. The training, roles and responsibilities of dietitians and nutritionists varied widely; in some centres dietitians were responsible for managing the diet, while in others this was performed by a physician. There were marked differences in target blood phenylalanine concentrations, the dosages of protein substitutes, systems for allocating daily phenylalanine allowance, and the definition of foods that could be eaten without restriction ('free foods'). Eighty percent (n=8/10) of centres encouraged breastfeeding together with protein substitute in infants with PKU.

CONCLUSIONS

Important differences exist among centres across Europe in the dietary management of PKU, and in support systems designed to assist patients in managing their diets. Further studies are needed to compare different dietary treatments with the aim of identifying best practice to optimise phenylalanine control and dietary adherence.

Optimizing the use of sapropterin (BH(4)) in the management of phenylketonuria

Phenylketonuria (PKU) is caused by mutations in the phenylalanine hydroxylase (PAH) gene, leading to deficient conversion of phenylalanine (Phe) to tyrosine and accumulation of toxic levels of Phe. A Phe-restricted diet is essential to reduce blood Phe levels and prevent long-term neurological impairment and other adverse sequelae. This diet is commenced within the first few weeks of life and current recommendations favor lifelong diet therapy. The observation of clinically significant reductions in blood Phe levels in a subset of patients with PKU following oral administration of 6R-tetrahydrobiopterin dihydrochloride (BH(4)), a cofactor of PAH, raises the prospect of oral pharmacotherapy for PKU. An orally active formulation of BH(4) (sapropterin dihydrochloride; Kuvan is now commercially available. Clinical studies suggest that treatment with sapropterin provides better Phe control and increases dietary Phe tolerance, allowing significant relaxation, or even discontinuation, of dietary Phe restriction. Firstly, patients who may respond to this treatment need to be identified. We propose an initial 48-h loading test, followed by a 1-4-week trial of sapropterin and subsequent adjustment of the sapropterin dosage and dietary Phe intake to optimize blood Phe control. Overall, sapropterin represents a major advance in the management of PKU.

L-carnitine blood levels and oxidative stress in treated phenylketonuric patients

AIMS

L-carnitine exerts an important role by facilitating the mitochondrial transport of fatty acids, but is also a scavenger of free radicals, protecting cells from oxidative damage. Phenylketonuria (PKU), an inborn error of phenylalanine (Phe) metabolism, is currently treated with a special diet consisting of severe restriction of protein-enriched foods, therefore potentially leading to L-carnitine depletion. The aim of this study was to determine L-carnitine levels and oxidative stress parameters in blood of two groups of PKU patients, with good and poor adherence to treatment.

METHODS

Treatment of patients consisted of a low protein diet supplemented with a synthetic amino acids formula not containing Phe, L-carnitine, and selenium. L-carnitine concentrations and the oxidative stress parameters thiobarbituric acid reactive species (TBARS) and total antioxidant reactivity (TAR) were measured in blood of the two groups of treated PKU patients and controls.

RESULTS

We verified a significant decrease of serum L-carnitine levels in patients who strictly adhered to the diet, as compared to controls and patients who did not comply with the diet. Furthermore, TBARS measurement was significantly increased and TAR was significantly reduced in both groups of phenylketonuric patients relatively to controls. We also found a significant negative correlation between TBARS and L-carnitine levels and a significant positive correlation between TAR and L-carnitine levels in well-treated PKU patients.

CONCLUSIONS

Our results suggest that L-carnitine should be measured in plasma of treated PKU patients, and when a decrease of this endogenous component is detected in plasma, supplementation should be considered as an adjuvant therapy.

Optimization of process parameters for the production of tyrosine phenol lyase by Citrobacterfreundii MTCC 2424

The process optimization using technological combinations for the production of tyrosine phenol lyase by Citrobacter freundii MTCC 2424 has been carried out in this study. The maximum production of tyrosine phenol lyase (0.15 U) was obtained by culturing C. freundii MTCC 2424 in a medium containing (g/l) meat extract 5.0, yeast extract 5.0, peptone 2.5, and l-tyrosine 1.0 at 25 degrees C for 16 h in a temperature controlled orbital shaker. A 2.5-fold increase in enzyme activity with 1.3-fold decrease in the cost of enzyme production (in terms of media components) was achieved by using different technological combinations. The process optimization using technological combinations allowed quick optimization of large number of variables, which helps in designing of suitable fermentation conditions for the cost-effective production of tyrosine phenol lyase. Moreover, this also provides information for balancing the nutrient concentration with minimum experimentation.

PKU in Minas Gerais State, Brazil: mutation analysis

This work was undertaken in order to ascertain the PKU mutational spectrum in Minas Gerais, Brazil, the relative frequency of the mutations in the State and the origin of these mutations by haplotype determination. Minas Gerais is a trihybrid population formed by miscegenation from Europeans, Africans and Amerindians. All 13 exons of the PAH gene from 78 PKU patients were analyzed, including splicing sites and the promoter region. We identified 30 different mutations and 98% of the PAH alleles were established. A new mutation (Q267X) was identified as well. The most common mutations found were V388M (21.2), R261Q (16.0%), IVS10-11G>A (15.3%), I65T (5.8%), IVS2+5G>C (5.8%), R252W (5.1%), IVS2+5G>A (4.5%), P281L (3.8%) and L348V (3.2%). These nine mutations correspond to 80% of the PKU alleles in the state. Haplotypes were determined to characterize the origin of the PAH alleles. The majority of the mutations found, with respective haplotypes, are frequent in the Iberian Peninsula. However, there were some mutations that are rare in Europe and four previously unreported mutation-haplotype associations. I65T and Q267X were found in association with haplotype 38 and may be African in origin or the result of miscegenation in the Brazilian population.

A 25-year longitudinal analysis of treatment efficacy in inborn errors of metabolism

We report here the results of treatment in a panel of 65 inborn errors of metabolism, obtained in the 25th year of a longitudinal project, first reported in 1983. The phenotypic impact of these 65 diseases was scored before and after treatment using a consistent set of parameters, which we have retained to measure change in clinical phenotype throughout the project. We observed significant improvements in the response to treatment for the disease set as a whole. The number of conditions for which there is no response to treatment has progressively decreased; from 31 in 1983, to 20 in 1993, to 17 in 2008. Concomitantly, there has been an increase in the number of conditions that fully respond to treatment (from 8 in 1983 and 1993, to 20 in 2008), and in those for which there is a partial response. Reasons for improved treatment responses include new small molecules, new enzyme replacement therapies, more conditions that can be treated by organ and cell transplantation, and new experimental approaches to substrate reduction and chaperone assisted therapy. However, the most important and new development was not found in one or other particular therapeutic modality but in the access to new knowledge surrounding the individual diseases via the Internet and related resources. Our longitudinal analysis of treatment efficacy for this subset of inborn errors of metabolism continues to constitute a robust and representative assessment of our ability to restore more normal homeostasis in the inborn errors of metabolism.