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

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

Natural history of children and adults with phenylketonuria in the NBS-PKU Connect registry.

PURPOSE: Phenylalanine hydroxylase deficiency, or phenylketonuria (PKU), is a rare autosomal recessive metabolic disorder. Early diagnosis via newborn screening (NBS) and initiation of treatment prevent the development of cognitive impairment and other co-morbidities. The purpose of this study is to describe the natural history of PKU in the United States, including prevalence of co-morbidities and predictors of outcomes. METHODS: We analyzed data from a self-report survey in the NBS-PKU Connect online registry. We describe the participants' nutrition management strategies, barriers to management, outcomes of bone disorders, skin, and psychological co-morbidities, and the use of special education or other special services. Predictors of outcomes were identified and assessed, including the impact of sex, age, age at diagnosis, blood phenylalanine concentration, use of sapropterin, use of medical food, adherence to prescribed diet, use of low protein modified foods, whether they had ever been off-diet, and use of tyrosine supplementation. RESULTS: The 219 respondents included individuals with PKU or hyperphenylalanemia (n = 78), or their caregivers (n = 141). Most (84.3%) started treatment before the age of two weeks. About one-third indicated that they had been off-diet at some point in their lives, and 81.4% reported that they currently adhered to their prescribed diet, with adherence to prescribed diet decreasing with age. Blood phenylalanine concentration was under the recommended threshold of 360 µmol/L for 68.5% of participants. One-quarter of respondents reported psychological co-morbidities, with anxiety and ADD/ADHD being the most common. The incidence of psychological co-morbidities increased with age and with ever having been off diet. Special education or other special services were more likely to be reported by individuals who were diagnosed after one week of age. Skin disorders such as acne and eczema were more common in females than males, and a minority of participants reported bone disorders. CONCLUSIONS: Despite recommendations to maintain blood phenylalanine concentrations in the therapeutic range throughout life, it is not uncommon for adults with PKU to discontinue dietary management of their disorder. Early diagnosis was associated with reduced need for special education or other special services, and continuous treatment was associated with decreased psychological co-morbidities.

The neurological and neuropsychiatric spectrum of adults with late-treated phenylketonuria.

INTRODUCTION: Phenylketonuria (PKU) is a rare, treatable inborn error of metabolism with frequent neurological and neuropsychiatric complications, especially in undiagnosed or insufficiently treated individuals. Given the wide range of clinical presentations and the importance of treatment implications, we here delineate the neurological and neuropsychiatric symptom spectrum in a large cohort of previously unreported adults with late-treated PKU. METHODS: We consecutively evaluated late-treated PKU cases and pooled clinical and paraclinical data, including video-material, from three centers with expertise in complex movement disorders, inborn errors of metabolism and pediatrics. RESULTS: 26 individuals were included (10 females, median age 52 years). Developmental delay and intellectual disability were omnipresent with severe impairment of expressive communication noted in 50% of cases. Movement disorders were prevalent (77%), including tremor (38%, mostly postural), stereotypies (38%), and tics (19%). One case had neurodegenerative levodopa-responsive parkinsonism. Mild ataxia was noted in 54% of cases and 31% had a history of seizures. Neuropsychiatric characteristics included obsessive-compulsive (35%) and self-injurious behaviors (31%), anxiety (27%), depression (19%) and features compatible with those observed in individuals with autism spectrum disorder (19%). Neuroimaging revealed mild white matter changes. Adherence to dietary treatment was inconsistent in the majority of cases, particularly throughout adolescence. CONCLUSION: A history of movement disorders, particularly tremor, stereotypies and tics, in the presence of developmental delay, intellectual disability and neuropsychiatric features, such as obsessive-compulsive and self-injurious behaviors in adults should prompt the diagnostic consideration of PKU. Initiation and adherence to (dietary) treatment can ameliorate the severity of these symptoms.

Nutrition status of adults with phenylketonuria treated with pegvaliase.

BACKGROUND: Pegvaliase is an enzyme substitution therapy that reduces blood phenylalanine (Phe) in adults with phenylketonuria (PKU), and often allows normalization of protein intake (≥0.8 g protein/kg). Here we examine the nutrition status of adults with PKU consuming a normal protein intake without medical food after being treated with pegvaliase for ≥1 year. METHODS: A cross-sectional study evaluating nutritional intake (3-day food record and food frequency questionnaire), anthropometrics, laboratory indices of protein, micronutrient, and essential fatty acid (EFA) status, and questionnaires evaluating food neophobia and Epicurean eating pleasure. RESULTS: Participants (n = 18, 61% female) started pegvaliase 4.9 ± 2.1 years prior to enrollment and were aged 38.2 ± 8.8 years with a mean BMI of 29.2 ± 4.1 kg/m2. Participants consumed a mean of 73.2 ± 17.6 g protein/d (1.0 ± 0.3 g/kg/d). Eleven participants had low blood Phe (<30 µmol/L) with adequate protein intake and normal indices of protein status. Micronutrient and EFA concentrations were normal except for mildly low vitamin D (<30 ng/mL, n = 12). Intakes of sodium, saturated fat, and added sugars exceeded recommendations for healthy adults, though mean diet quality was comparable to a US adult reference population. Lower food neophobia scores correlated with an increased aesthetic appreciation of food. However, 53% of participants self-reported having moderate (n = 6) to high (n = 3) food neophobia. DISCUSSION: Participants treated with pegvaliase consumed an unrestricted diet with adequate dietary protein and, overall, had normal protein, micronutrient, and fatty acid status. Despite low blood Phe, protein nutriture was not compromised. While nutritional deficiencies were not identified, diet quality was suboptimal and some participants reported food neophobia. Nutrition education remains an important component of care as patients adapt to a normal diet.

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

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

Insights from Animal Models on the Pathophysiology of Hyperphenylalaninemia: Role of Mitochondrial Dysfunction, Oxidative Stress and Inflammation.

Phenylketonuria (PKU) is an inborn error of metabolism caused by phenylalanine hydroxylase (PAH) deficiency and characterized by elevated plasma levels of phenylalanine (hyperphenylalaninemia-HPA). In severe cases, PKU patients present with neurological dysfunction and hepatic damage, but the underlying mechanisms are not fully elucidated. Other forms of HPA also characterized by neurological symptoms occur in rare instances due to defects in the metabolism of the PAH cofactor tetrahydrobiopterin. This review aims to gather the knowledge acquired on the phenylalanine-induced toxicity focusing on findings obtained from pre-clinical studies. Mounting evidence obtained from PKU genetic mice, rats submitted to different HPA models, and cell cultures exposed to phenylalanine has shown that high levels of this amino acid impair mitochondrial bioenergetics, provoke changes in oxidative and inflammatory status, and induce apoptosis. Noteworthy, some data demonstrated that phenylalanine-induced oxidative stress occurs specifically in mitochondria. Further studies have shown that the metabolites derived from phenylalanine, namely phenylpyruvate, phenyllactate, and phenylacetate, also disturb oxidative status. Therefore, it may be presumed that mitochondrial damage is one of the most important mechanisms responsible for phenylalanine toxicity. It is expected that the findings reviewed here may contribute to the understanding of PKU and HPA pathophysiology and to the development of novel therapeutic strategies for these disorders.

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

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

GTP-cyclohydrolase deficiency induced peripheral and deep microcirculation dysfunction with age.

The present study assessed the impact of impaired tetrahydrobiopterin (BH4) production on vasoreactivity from conduit and small arteries along the vascular tree as seen during aging. For this purpose, the mutant hyperphenylalaninemic mouse (hph-1) was used. This model is reported to be deficient in GTP cyclohydrolase I, a rate limiting enzyme in BH4 biosynthesis. BH4 is a key regulator of vascular homeostasis by regulating the nitric oxide synthase 3 (NOS3) activity. In GTP-CH deficient mice, the aortic BH4 levels were decreased, by -77% in 12 week-middle-aged mice (young) and by -83% in 35-45 week-middle-aged mice (middle-aged). In young hph-1, the mesenteric artery ability to respond to flow was slightly reduced by 9%. Aging induced huge modification in many vascular functions. In middle-aged hph-1, we observed a decrease in aortic cGMP levels, biomarker of NO availability (-46%), in flow-mediated vasodilation of mesenteric artery (-31%), in coronary hyperemia response measured in isolated heart following transient ischemia (-27%) and in cutaneous microcirculation dilation in response to acetylcholine assessed in vivo by laser-doppler technic (-69%). In parallel, the endothelium-dependent relaxation in response to acetylcholine in conduit blood vessel, measured on isolated aorta rings, was unchanged in hph-1 mice whatever the age. Our findings demonstrate that in middle-aged GTP-CH depleted mice, the reduction of BH4 was characterized by an alteration of microcirculation dilatory properties observed in various parts of the vascular tree. Large conduit blood vessels vasoreactivity, ie aorta, was unaltered even in middle-aged mice emphasizing the main BH4-deletion impact on the microcirculation.

Nutrition, Microbiota and Role of Gut-Brain Axis in Subjects with Phenylketonuria (PKU): A Review.

The composition and functioning of the gut microbiota, the complex population of microorganisms residing in the intestine, is strongly affected by endogenous and exogenous factors, among which diet is key. Important perturbations of the microbiota have been observed to contribute to disease risk, as in the case of neurological disorders, inflammatory bowel disease, obesity, diabetes, cardiovascular disease, among others. Although mechanisms are not fully clarified, nutrients interacting with the microbiota are thought to affect host metabolism, immune response or disrupt the protective functions of the intestinal barrier. Similarly, key intermediaries, whose presence may be strongly influenced by dietary habits, sustain the communication along the gut-brain-axis, influencing brain functions in the same way as the brain influences gut activity. Due to the role of diet in the modulation of the microbiota, its composition is of high interest in inherited errors of metabolism (IEMs) and may reveal an appealing therapeutic target. In IEMs, for example in phenylketonuria (PKU), since part of the therapeutic intervention is based on chronic or life-long tailored dietetic regimens, important variations of the microbial diversity or relative abundance have been observed. A holistic approach, including a healthy composition of the microbiota, is recommended to modulate host metabolism and affected neurological functions.

Dietary intake and nutritional status of patients with phenylketonuria in Taiwan.

Phenylalanine hydroxylase (PAH) deficiency leads to phenylalanine accumulation and results in phenylketonuria (PKU). Phenylketonuria can contribute to severe inability such as mental impairment. Early diagnosis and dietary intervention can have beneficial effects on maintaining normal neural and cognitive function in patients with PKU. However, a long-term low phenylalanine diet may put children at risk of malnutrition. A food supplement was therefore used for children with PKU under dietician supervision according to dietary reference intakes (DRIs). In this cross-sectional study, we enrolled patients with PKU and age-matched controls to compare their anthropometry data [weight, height, body mass index (BMI), and body composition using bioelectrical impedance analysis (BIA)], and correlated it with their dietary intake based on 24-h dietary recall. For continuous parameters, the data were expressed as median ± standard deviation (SD), and the Mann-Whitney U test was used to test the difference among the groups. Correlation by natural proteins, body fat, and fat-free mass were evaluated using the Pearson correlation coefficient. Twenty-two participants diagnosed with PKU (ages 8-27 years; mean 15.23 ± 5.23) and a control group of 22 non-PKU participants (ages 8-39 years; mean 19.73 ± 10.6) were recruited for this study. Between the two groups of participants, no significant difference was found in height, weight, BMI, muscle mass, or fat mass. The percentage of natural protein has no effect on body composition. We found a significant positive correlation between the total protein intake percentage of DRIs and muscle mass (r = 0.491, p = 0.020) and a significant negative correlation in the total protein intake percentage of DRIs and fat mass (r = -0.475, p = 0.025) in participants with PKU. There were no significant differences in body composition and nutrition intake between patients with PKU (under metabolic control) and healthy subjects. Thus, giving proper nutrition treatment may have beneficial effects on body growth and nutrition status in patients with PKU in Taiwan.

The Impact of the Use of Glycomacropeptide on Satiety and Dietary Intake in Phenylketonuria.

Protein is the most satiating macronutrient, increasing secretion of gastrointestinal hormones and diet induced thermogenesis. In phenylketonuria (PKU), natural protein is restricted with approximately 80% of intake supplied by a synthetic protein source, which may alter satiety response. Casein glycomacropeptide (CGMP-AA), a carbohydrate containing peptide and alternative protein substitute to amino acids (AA), may enhance satiety mediated by its bioactive properties. AIM: In a three-year longitudinal; prospective study, the effect of AA and two different amounts of CGMP-AA (CGMP-AA only (CGMP100) and a combination of CGMP-AA and AA (CGMP50) on satiety, weight and body mass index (BMI) were compared. METHODS: 48 children with PKU completed the study. Median ages of children were: CGMP100; (n = 13), 9.2 years; CGMP50; (n = 16), 7.3 years; and AA (n = 19), 11.1 years. Semi-quantitative dietary assessments and anthropometry (weight, height and BMI) were measured every three months. RESULTS: The macronutrient contribution to total energy intake from protein, carbohydrate and fat was similar across the groups. Adjusting for age and gender, no differences in energy intake, weight, BMI, incidence of overweight or obesity was apparent between the groups. CONCLUSION: In this three-year longitudinal study, there was no indication to support a relationship between CGMP and satiety, as evidenced by decreased energy intake, thereby preventing overweight or obesity. Satiety is a complex multi-system process that is not fully understood.

Lipids and phenylketonuria: Current evidences pointed the need for lipidomics studies.

Phenylketonuria (PKU) is the most prevalent inborn error of amino acid metabolism. The disease is due to the deficiency of phenylalanine (Phe) hydroxylase activity, which causes the accumulation of Phe. Early diagnosis through neonatal screening is essential for early treatment implementation, avoiding cognitive impairment and other irreversible sequelae. Treatment is based on Phe restriction in the diet that should be maintained throughout life. High dietary restrictions can lead to imbalances in specific nutrients, notably lipids. Previous studies in PKU patients revealed changes in levels of plasma/serum lipoprotein lipids, as well as in fatty acid profile of plasma and red blood cells. Most studies showed a decrease in important polyunsaturated fatty acids, namely DHA (22:6n-3), AA (20:4n-6) and EPA (20:5n-6). Increased oxidative stress and subsequent lipid peroxidation have also been observed in PKU. Despite the evidences that the lipid profile is changed in PKU patients, more studies are needed to understand in detail how lipidome is affected. As highlighted in this review, mass spectrometry-based lipidomics is a promising approach to evaluate the effect of the diet restrictions on lipid metabolism in PKU patients, monitor their outcome, namely concerning the risk for other chronic diseases, and find possible prognosis biomarkers.

Impact of phenylalanine on cognitive, cerebral, and neurometabolic parameters in adult patients with phenylketonuria (the PICO study): a randomized, placebo-controlled, crossover, noninferiority trial.

BACKGROUND: The population of adult patients with early-treated phenylketonuria (PKU) following newborn screening is growing substantially. The ideal target range of blood phenylalanine (Phe) levels in adults outside pregnancy is a matter of debate. Therefore, prospective intervention studies are needed to evaluate the effects of an elevated Phe concentration on cognition and structural, functional, and neurometabolic parameters of the brain. METHODS: The PICO (Phenylalanine and Its Impact on Cognition) Study evaluates the effect of a 4-week Phe load on cognition and cerebral parameters in adults with early-treated PKU in a double-blind, randomized, placebo-controlled, crossover, noninferiority trial. PARTICIPANTS: Thirty adult patients with early-treated PKU and 30 healthy controls comparable to patients with regard to age, sex, and educational level will be recruited from the University Hospitals Bern and Zurich, Switzerland. Patients are eligible for the study if they are 18 years of age or older and had PKU diagnosed after a positive newborn screening and were treated with a Phe-restricted diet starting within the first 30 days of life. INTERVENTION: The cross-over intervention consists of 4-week oral Phe or placebo administration in patients with PKU. The study design mimics a Phe-restricted and a Phe-unrestricted diet using a double-blinded, placebo-controlled approach. OBJECTIVES: The primary objective of the PICO Study is to prospectively assess whether a temporarily elevated Phe level influences cognitive performance (working memory assessed with a n-back task) in adults with early-treated PKU. As a secondary objective, the PICO Study will elucidate the cerebral (fMRI, neural activation during a n-back task; rsfMRI, functional connectivity at rest; DTI, white matter integrity; and ASL, cerebral blood flow) and neurometabolic mechanisms (cerebral Phe level) that accompany changes in Phe concentration. Cognition, and structural and functional parameters of the brain of adult patients with early-treated PKU will be cross-sectionally compared to healthy controls. All assessments will take place at the University Hospital Bern, Switzerland. RANDOMIZATION: Central randomization will be used to assign participants to the different treatment arms with age, sex, and center serving as the stratification factors. Randomization lists will be generated by an independent statistician. Blinding: All trial personnel other than the statistician generating the randomization list and the personnel at the facility preparing the interventional product are blinded to the assigned treatment. DISCUSSION: Using a combination of neuropsychological and neuroimaging data, the PICO Study will considerably contribute to improve the currently insufficient level of evidence on how adult patients with early-treated PKU should be managed. TRIAL REGISTRATION: The study is registered at clinicaltrials.gov (NCT03788343) on the 27th of December 2018, at kofam.ch (SNCTP000003117) on the 17th of December 2018, and on the International Clinical Trials Registry Platform of the WHO.

True Restriction in Diffusion-Weighted Imaging in a Mistreated Patient With Phenylketonuria.

INTRODUCTION: Phenylketonuria (PKU) is the most common inborn error of amino acid metabolism and causes neurological manifestations because of excessive accumulation of phenylalanine (PHE). It can also affect adult patients who discontinue their treatment, even if they had been under adequate metabolic control during childhood. For that reason, it is recommended that PKU treatment should be continued throughout life and target PHE levels for adult patients should range between 120 and 600 µmol/L. CASE REPORT: The authors present an adult patient with PKU who discontinued treatment and developed cognitive dysfunction because of high blood levels of PHE. Brain magnetic resonance imaging (MRI) of the patient was characteristic for PKU, presenting periventricular and callosal white matter hyperintensities in T2 and fluid-attenuated inversion recovery sequences, which were additionally associated with true restriction in diffusion-weighted imaging sequence, a far less recognized PKU neuroimaging feature. DISCUSSION: Cognitive dysfunction and psychiatric disorders can be present in adult patients with PKU who discontinue treatment and have poor PHE metabolic control. The presence of white matter hyperintensities in T2 and fluid-attenuated inversion recovery MRI-sequences is a well-described neuroimaging feature of PKU, but diffusion-weighted imaging sequence may also be reliable in detecting brain lesions in patients with PKU. PKU lesions should be considered in the differential diagnosis of true diffusion restriction in brain MRI of patients with PKU history or those who might have escaped newborn screening diagnosis but present neurocognitive dysfunction. Appropriate treatment for the management of PKU should be initiated for the reversal of the clinical and neuroimaging findings.

Bone mineral density is within normal range in most adult phenylketonuria patients.

Low bone mineral density (BMD) as a risk factor for fractures has been a long-standing concern in phenylketonuria (PKU). It is hypothesised that the disease itself or the dietary treatment might lead to a low BMD. Previous studies show conflicting results of BMD in PKU due to differences in age, techniques to assess BMD and criteria used. To assess the prevalence of low BMD and define possible risk factors in a large number of adult, early treated PKU (ETPKU) patients. European centres were invited for a survey, collecting retrospective data including results of dual-energy X-ray absorptiometry (DXA) scans of adult ETPKU patients. BMD of 183 adult ETPKU patients aged 18-46 (median age 28, all females premenopausal) years was lower than in the general population at most skeletal sites but the frequency of low BMD (Z-score <-2) was at maximum 5.5%. No risk factors for low BMD in PKU patients could be identified. Low BMD occurs only in a small subset of PKU patients. DXA scans should be considered for well controlled patients from age 35-40 years and up and on indication in those PKU patients considered to be at increased risk for fractures.

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.

5-year retrospective analysis of patients with phenylketonuria (PKU) and hyperphenylalaninemia treated at two specialized clinics.

BACKGROUND: Phenylketonuria (PKU) is an autosomal recessive disease caused by mutations in the PAH gene, resulting in deficiency of phenylalanine hydroxylase (PAH), an enzyme that converts phenylalanine (Phe) to tyrosine (Tyr). The purpose of this study was to capture real-world data associated with managing PKU under current standard of care and to characterize a representative population for a planned gene therapy trial. METHODS: A retrospective chart review was conducted at two U.S. clinics for individuals 10-40 years old diagnosed with PKU-related hyperphenylalaninemia (HPA). Demographics, medical history, treatments and blood Phe data were collected from electronic medical records spanning a five-year period ending in November 2017. RESULTS: 152 patients were enrolled (65.8% had classical PKU). Although >95% of patients were prescribed a Phe-restricted diet, blood Phe concentrations remained substantially elevated, particularly in patients diagnosed with classical PKU. As the Phe threshold was lowered (Phe < 600, 360, 120 or 30 µmol/L), the number of patients with consecutive lab values below the threshold decreased, suggesting that many patients' Phe levels are inadequately controlled. 62.5% of patients were reported as having a history of at least one neuropsychiatric comorbidity, and adults were more likely than adolescents (69.5% vs. 54.3%). 92 of 98 PAH genotypes collected were distinct mutations; the 6 null-null genotypes were associated with classical PKU. Overall the demographics and clinical data were consistent across both sites. CONCLUSION: Despite dietary restrictions, mean Phe concentrations were > 360 µmol/L (a level considered well-controlled based on current U.S. treatment guidelines) for mild, moderate, and classical PKU patients. There remains an unmet need for therapies to control Phe concentrations.

Adult cognitive outcomes in phenylketonuria: explaining causes of variability beyond average Phe levels.

OBJECTIVE: The objective was to deepen the understanding of the causes of individual variability in phenylketonuria (PKU) by investigating which metabolic variables are most important for predicting cognitive outcomes (Phe average vs Phe variation) and by assessing the risk of cognitive impairment associated with adopting a more relaxed approach to the diet than is currently recommended. METHOD: We analysed associations between metabolic and cognitive measures in a mixed sample of English and Italian early-treated adults with PKU (N = 56). Metabolic measures were collected through childhood, adolescence and adulthood; cognitive measures were collected in adulthood. Metabolic measures included average Phe levels (average of median values for each year in a given period) and average Phe variations (average yearly standard deviations). Cognition was measured with IQ and a battery of cognitive tasks. RESULTS: Phe variation was as important, if not more important, than Phe average in predicting adult outcomes and contributed independently. Phe variation was particularly detrimental in childhood. Together, childhood Phe variation and adult Phe average predicted around 40% of the variation in cognitive scores. Poor cognitive scores (> 1 SD from controls) occurred almost exclusively in individuals with poor metabolic control and the risk of poor scores was about 30% higher in individuals with Phe values exceeding recommended thresholds. CONCLUSIONS: Our results provide support for current European guidelines (average Phe value = < 360 µmol/l in childhood; = < 600 µmo/l from 12 years onwards), but they suggest an additional recommendation to maintain stable levels (possibly Phe SD = < 180 µmol/l throughout life). PUBLIC SIGNIFICANCE STATEMENTS: We investigated the relationship between how well people with phenylketonuria control blood Phe throughout their life and their ability to carry out cognitive tasks in adulthood. We found that avoiding blood Phe peaks was as important if not more important that maintaining average low Phe levels. This was particularly essential in childhood. We also found that blood Phe levels above recommended European guidelines was associated with around 30% increase in the risk of poor cognitive outcomes.

[Early diagnosis of phenylketonuria. Physiopathology of the neuronal damage and therapeutic options]. / Fenilcetonuria de diagnóstico precoz. Bases fisiopatológicas del daño neuronal y opciones terapéuticas.

Phenylketonuria, also known as PKU, is the most frequent congenital inborn error of metabolism. The severe form or classic PKU untreated causes intellectual disability, although with the early detection programs in the neonatal period, diagnosis and treatment prevent the appearance of the symptoms. Despite early diagnosis and treatment we have observed some neurotoxicity in treated PKU patients. We analyzed the factors involved apart from the toxicity due to the high cerebral concentrations of phenylalanine (Phe), the defects of synthesis of neurotransmitters, the alteration of cerebral myelination, the effect of the elevation of Phe in the processes of transport and distribution of neutral amino acids with an abnormal synthesis of brain proteins, plasma and cerebral tyrosine deficiency, the neurotoxicity of Phe metabolites, the defect of cholesterol biosynthesis or the increase of oxidative stress. White matter alterations in early treated PKU patients have an important role in neurological manifestations. The treatment of PKU is for life and is based on the reduction of foods containing Phe combined with the administration of a special formula or tetrahydrobiopterin (BH4) treatment. New therapeutic options will be analyzed.

La fenilcetonuria, también conocida como PKU, es el error congénito más frecuente del metabolismo de los aminoácidos. La forma grave o PKU clásica no tratada, causa una discapacidad intelectual, aunque los programas de detección en el período neonatal, el diagnóstico y el tratamiento evitan la aparición de los síntomas. A pesar de un diagnóstico y tratamiento temprano hemos observado cierta neurotoxicidad en los pacientes con PKU tratados. Analizamos los demás factores implicados, aparte de la toxicidad por las elevadas concentraciones cerebrales de fenilalanina (Phe), se revisan los defectos de síntesis de neurotransmisores, las alteración de la mielinización cerebral, el efecto de la elevación de Phe en los procesos de transporte y distribución de los aminoácidos neutros con una síntesis anómala de proteínas cerebrales, la deficiencia plasmática y cerebral de tirosina, la neurotoxicidad de los metabolitos de Phe, el defecto de la biosíntesis del colesterol o el aumento del estrés oxidativo. Las alteraciones de la sustancia blanca en los pacientes con PKU tienen un papel importante en las manifestaciones neurológicas. El tratamiento de la PKU es para toda la vida y se basa en la reducción del aporte de alimentos que contienen Phe combinado con la administración de una fórmula especial, o en el tratamiento con tetrahidrobiopterina (BH4). Se analizan nuevas opciones terapéuticas.

Structure of full-length wild-type human phenylalanine hydroxylase by small angle X-ray scattering reveals substrate-induced conformational stability.

Human phenylalanine hydroxylase (hPAH) hydroxylates L-phenylalanine (L-Phe) to L-tyrosine, a precursor for neurotransmitter biosynthesis. Phenylketonuria (PKU), caused by mutations in PAH that impair PAH function, leads to neurological impairment when untreated. Understanding the hPAH structural and regulatory properties is essential to outline PKU pathophysiological mechanisms. Each hPAH monomer comprises an N-terminal regulatory, a central catalytic and a C-terminal oligomerisation domain. To maintain physiological L-Phe levels, hPAH employs complex regulatory mechanisms. Resting PAH adopts an auto-inhibited conformation where regulatory domains block access to the active site. L-Phe-mediated allosteric activation induces a repositioning of the regulatory domains. Since a structure of activated wild-type hPAH is lacking, we addressed hPAH L-Phe-mediated conformational changes and report the first solution structure of the allosterically activated state. Our solution structures obtained by small-angle X-ray scattering support a tetramer with distorted P222 symmetry, where catalytic and oligomerisation domains form a core from which regulatory domains protrude, positioning themselves close to the active site entrance in the absence of L-Phe. Binding of L-Phe induces a large movement and dimerisation of regulatory domains, exposing the active site. Activated hPAH is more resistant to proteolytic cleavage and thermal denaturation, suggesting that the association of regulatory domains stabilises hPAH.