Neuropsychological Profile of Children with Early and Continuously Treated Phenylketonuria: Systematic Review and Future Approaches

Psychiatric Manifestations in Children and Adolescents with Inherited Metabolic Diseases

Background: Inherited metabolic disorders (IEMs) can be represented in children and adolescents by psychiatric disorders. The early diagnosis of IEMs is crucial for clinical outcome and treatment. The aim of this review is to analyze the most recurrent and specific psychiatric features related to IEMs in pediatrics, based on the onset type and psychiatric phenotypes. Methods: Following the PRISMA Statement, a systematic literature review was performed using a predefined algorithm to find suitable publications in scientific databases of interest. After removing duplicates and screening titles and abstracts, suitable papers were analyzed and screened for inclusion and exclusion criteria. Finally, the data of interest were retrieved from the remaining articles. Results: The results of this study are reported by type of symptoms onset (acute and chronic) and by possible psychiatric features related to IEMs. Psychiatric phenomenology has been grouped into five main clinical manifestations: mood and anxiety disorders; schizophrenia-spectrum disorders; catatonia; eating disorders; and self-injurious behaviors. Conclusions: The inclusion of a variety of psychiatric manifestations in children and adolescents with different IEMs is a key strength of this study, which allowed us to explore the facets of seemingly different disorders in depth, avoiding possible misdiagnoses, with the related delay of early and appropriate treatments.

Executive functions in preschool children with moderate hyperphenylalaninemia and phenylketonuria: a prospective study

BACKGROUND

The risk of neuropsychological disorders appears to be high in hyperphenylalaninemia (HPA). The hypothesis of executive function impairment is prominent in accounting for the neuropsychological phenotype in phenylketonuria (PKU) and is suspected in moderate hyperphenylalaninemia (MHP). However, the issue of early onset of executive disorders remains. The aim of this study was to explore the hypothesis of early executive dysfunction in HPA patients and the possible links with certain metabolic variables according to the new international classifications for patients with PKU and MHP. A group of 23 HPA children (12 PKU, 11 MHP) aged 3 to 5 years was included and compared to 50 control children. The two groups were comparable in terms of socio-demographics (age, sex, parental education level). Executive functions were assessed using performance-based tests and daily life questionnaires (parents and teachers).

RESULTS

Preschool HPA patients have comparable executive scores to control subjects. In contrast, PKU patients score significantly worse than MHP patients on 3 executive tests (verbal working memory, visual working memory and cognitive inhibition. There is no executive complaints in daily life (parents and teachers) for the 2 groups of patients. In addition, 3 correlations were identified between executive scores and Phe levels at inclusion, mean Phe level and variability of Phe levels throughout life.

CONCLUSIONS

Thus, there appears to be evidence of early executive dysfunction in PKU preschool-children, but not in MHP children. Occasionally, certain metabolic indicators can predict executive difficulties in young children with PKU.

Neuropsychological assessment of adults with phenylketonuria using the NIH toolbox

Among researchers and clinicians, there is a call for the development and validation of new measures to better assess and characterize neurocognitive difficulties associated with early-treated phenylketonuria (ETPKU) and other metabolic disorders. The NIH Toolbox represents a relatively new computer-administered assessment tool and provides a sampling of performance across multiple cognitive domains, several of which (e.g., executive function, processing speed) are at risk for disruption in ETPKU. The goal of the present study was to provide an initial evaluation of the value and sensitivity of the NIH Toolbox for use with individuals with ETPKU. To this end, a sample of adults with ETPKU and a demographically-matched comparison group without PKU completed the cognitive and motor batteries of the Toolbox. Results indicate that overall performance (as reflected by the Fluid Cognition Composite) was sensitive to both group differences (ETPKU vs non-PKU) as well as blood Phe levels (a marker of metabolic control). The present findings offer preliminary support for the utility of the NIH Toolbox as a measure of neurocognitive functioning in individuals with ETPKU. Future research including a larger sample size and broader age range is needed to fully validate the Toolbox for clinical and research use with individuals with ETPKU.

The impact of metabolic control on cognition, neurophysiology, and well-being in PKU: A systematic review and meta-analysis of the within-participant literature

Phenylketonuria (PKU) is a metabolic disease where Phenylalanine (Phe) rises much above normal levels. Cross-sectional and correlational studies provide valuable information on the importance of maintaining low blood-Phe to achieve good outcomes, but they may be confounded, at least partially, by differences in participant demographics. Moreover, the effect of Phe at older ages is difficult to ascertain because of strong associations between Phe levels across ages. Within-participant studies avoid confounding issues. We have reviewed these studies. We followed PRISMA guidelines to search the literature for studies reporting the impact of Phe changes within participants. Phe was either increased or decreased through diet relaxation/resumption or through pharmacological interventions. Forty-six separate articles reported, singly or in combination, results on cognition (N = 37), well-being (N = 22) and neurophysiological health (N = 14). For all studies, we established, in a binary way, whether a benefit of lower Phe was or was not demonstrated and compared numbers showing benefit versus a null or negative outcome. We then analyzed whether critical parameters (e.g., length of the study/condition for the change, size of Phe change achieved) influenced presence or absence of benefit. For a subset of studies that reported quantitative cognitive outcomes, we carried out a meta-analysis to estimate the size of change in cognitive performance associated with a change in Phe and its significance. There were significantly more studies with benefits than no benefits, both for cognitive and well-being outcomes, and a trend in this direction for neurophysiological outcomes. The meta-analysis showed a highly significant effect size both overall (0.55) and when studies with adults/adolescents were considered separately (0.57). There was some indication that benefits were easier to demonstrate when differences in Phe were larger and achieved across a longer period, but these effects were not always consistent. These results reinforce results from the literature by demonstrating the importance of lower Phe in children as well as in adolescents and adults, even when confounding factors in group composition are eliminated. The field would benefit from further studies where Phe levels are contrasted within-participants to ascertain how much Phe needs to be changed and for how long to see a difference and which measures demonstrate a difference (e.g., which cognitive tasks).

Neuropsychological Disorders in Moderate Hyperphenylalaninemia: Literature Review

Moderate hyperphenylalaninemia (mHPA) is a hydroxylase deficiency corresponding to phenylalanine levels, at newborn screening, below 360 μmol/l. The neurological impact of mHPA is usually considered to be very low, but few studies have investigated the neuropsychological profile of mHPA patients.A systematic review of the neuropsychological aspects of mHPA was therefore conducted.The results showed a preservation of cognitive functions (intelligence, memory, visuoperception…). However, several indicators point to executive difficulties in this population. In regard to the important impact of executive functions in daily life, it is essential to conduct other studies in mHPA patients by proposing an integrative approach.

Meta-analyses of cognitive functions in early-treated adults with phenylketonuria

Our study estimated size of impairment for different cognitive functions in early-treated adults with PKU (AwPKU) by combining literature results in a meta-analytic way. We analysed a large set of functions (N = 19), each probed by different measures (average = 12). Data were extracted from 26 PKU groups and matched controls, with 757 AwPKU contributing 220 measures. Effect sizes (ESs) were computed using Glass' ∆ where differences in performance between clinical/PKU and control groups are standardized using the mean and standard deviation of the control groups. Significance was assessed using measures nested within independent PKU groups as a random factor. The weighted Glass' ∆ was - 0.44 for all functions taken together, and - 0.60 for IQ, both highly significant. Separate, significant impairments were found for most functions, but with great variability (ESs from -1.02 to -0.18). The most severe impairments were in reasoning, visual-spatial attention speed, sustained attention, visuo-motor control, and flexibility. Effect sizes were larger with speed than accuracy measures, and with visuo-spatial than verbal stimuli. Results show a specific PKU profile that needs consideration when monitoring the disease.

A comprehensive assessment of neurocognitive and psychological functioning in adults with early-treated phenylketonuria

OBJECTIVE

Relative to youth with early-treated phenylketonuria (ETPKU), much less is known regarding the cognitive profile of adults with ETPKU. The present study aimed to address this gap by providing a comprehensive assessment of neuropsychological functioning among adults with ETPKU.

METHOD

A sample of 40 adults with ETPKU (ages 18 - 36) and a demographically matched group of 32 healthy individuals without PKU participated. Participants completed a comprehensive neuropsychological battery including the NIH Toolbox, Wechsler Abbreviated Scale of Intelligence - Second Edition (WASI-II), Conners' Continuous Performance Test (CPT-3), select subtests from the Weschler Adult Intelligence Scale - Fourth Edition (WAIS-IV) as well as several self-report measures of cognitive and psychoemotional functioning. Scores from these tests were combined to create cognitive composites reflecting overall task performance in the areas of verbal ability, visuospatial skills, executive functioning, motor skills, and processing speed.

RESULTS

No group differences were observed for full scale IQ or verbal ability. However, individuals with ETPKU demonstrated poorer performance on measures of executive functioning, processing speed, motor skills, and visuospatial skills as compared to the non-PKU group. Within the ETPKU group, recent blood phenylalanine levels (an indicator of metabolic control) were significantly correlated with performance across most cognitive domains and aspects of psychological functioning.

CONCLUSIONS

Present findings suggest that the neuropsychological profile of adult ETPKU is characterized by circumscribed impairments in select cognitive domains. In addition, the results underscore the importance of maintaining metabolic control across the lifespan in individuals with ETPKU.

Neurocognitive outcome and mental health in children with tyrosinemia type 1 and phenylketonuria: A comparison between two genetic disorders affecting the same metabolic pathway

Tyrosinemia type 1 (TT1) and phenylketonuria (PKU) are both inborn errors of phenylalanine-tyrosine metabolism. Neurocognitive and behavioral outcomes have always featured in PKU research but received less attention in TT1 research. This study aimed to investigate and compare neurocognitive, behavioral, and social outcomes of treated TT1 and PKU patients. We included 33 TT1 patients (mean age 11.24 years; 16 male), 31 PKU patients (mean age 10.84; 14 male), and 58 age- and gender-matched healthy controls (mean age 10.82 years; 29 male). IQ (Wechsler-subtests), executive functioning (the Behavioral Rating Inventory of Executive Functioning), mental health (the Achenbach-scales), and social functioning (the Social Skills Rating System) were assessed. Results of TT1 patients, PKU patients, and healthy controls were compared using Kruskal-Wallis tests with post-hoc Mann-Whitney U tests. TT1 patients showed a lower IQ and poorer executive functioning, mental health, and social functioning compared to healthy controls and PKU patients. PKU patients did not differ from healthy controls regarding these outcome measures. Relatively poor outcomes for TT1 patients were particularly evident for verbal IQ, BRIEF dimensions "working memory", "plan and organize" and "monitor", ASEBA dimensions "social problems" and "attention problems", and for the SSRS "assertiveness" scale (all p values <0.001). To conclude, TT1 patients showed cognitive impairments on all domains studied, and appeared to be significantly more affected than PKU patients. More attention should be paid to investigating and monitoring neurocognitive outcome in TT1 and research should focus on explaining the underlying pathophysiological mechanism.

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.

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

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

Executive functions in preschool-aged children with neurofibromatosis type 1: Value for early assessment

Introduction: Executive functions (EFs) impairment is common in children with neurofibromatosis type 1 (NF1), and could be a significant vulnerability associated with this medical disorder. However, we still know little about EFs in preschool NF1. Our study assessed EFs in NF1 children using performance-based tests and daily life questionnaires, which combined the views of parents and teachers.Method: Seven classic experimental tasks were used to evaluate EFs in 33 NF1 children aged 3 to 5 years old, and BRIEF-P questionnaires were completed by their parents and teachers. These children's performance was compared with a control group of 52 healthy children matched in age, gender and socio-cultural status.Results: NF1 children have significantly lower scores for 5 out of 7 executive tasks than control children and significantly higher levels of EF concerns in the parent and teacher BRIEF-P ratings. The correlations between performance-based tests and questionnaires are weak.Conclusions: Our results support an early executive dysfunction in NF1 children and call for early and systematic assessment of EFs. Both performance-based tests and questionnaires are complementary tools to investigate early EFs dysfunction in children with NF1.

Occurrence of Inborn Errors of Metabolism in Newborns, Diagnosis and Prophylaxis

Inborn errors of metabolism (IEM) are a heterogeneous group of rare genetic disorders that are generally transmitted as autosomal or X-linked recessive disorders. These defects arise due to mutations associated with specific gene(s), especially the ones associated with key metabolic enzymes. These enzymes or their product(s) are involved in various metabolic pathways, leading to the accumulation of intermediary metabolite(s), reflecting their toxic effects upon mutations. The diagnosis of these metabolic disorders is based on the biochemical analysis of the clinical manifestations produced and their molecular mechanism. Therefore, it is imperative to devise diagnostic tests with high sensitivity and specificity for early detection of IEM. Recent advances in biochemical and polymerase chain reaction-based genetic analysis along with pedigree and prenatal diagnosis can be life-saving in nature. The latest development in exome sequencing for rapid diagnosis and enzyme replacement therapy would facilitate the successful treatment of these metabolic disorders in the future. However, the longterm clinical implications of these genetic manipulations is still a matter of debate among intellectuals and requires further research.

[Phenylketonuria, from diet to gene therapy]

The prognosis for phenylketonuria (PKU) has been improved by neonatal screening and dietary management via a low-phenylalanine diet. This treatment must be followed throughout life, which induces severe compliance problems. Drug treatment with sapropterin (or BH4) has come to help a reduced percentage of patients who respond to this drug. A subcutaneous enzyme therapy is available in the USA and has obtained European marketing authorization, but generates significant side effects, which limits its effectiveness. New therapeutic options for PKU are currently being developed, in particular gene therapy. The purpose of this article is to take stock of the pathophysiology and the various new therapeutic modalities currently in development.

Sustaining benefits of nutritional therapy in young adults with phenylketonuria - A 2 year prospective study

Introduction

Phenylketonuria (PKU) is an inborn error of metabolism, which is caused by a deficiency in the enzyme phenylalanine hydroxylase (PAH). Life-long Phe-free diet impairs quality of life, especially in adolescents and young adults which take responsibility over their diet and therapy from their parents, but expect freedom in daily routine.

Methods and results

105 patients with PKU were screened for eligibility for participating in this study. Data of 21 patients with genetic predictive value (GPV) ≤5 and age between 14 and 30 years were included in the analysis. Mean age of the study population was 22.6 ± 7.5 years, 8 patients (38%) were female. At baseline, structured counselling by a professional nutrionist was performed.

Mean Phe-level at baseline was 926 ± 432 μmol/l, after six months Phe-levels were significantly reduced to 709 ± 314 μmol/l (p = .039), in total 4 additional patients (38% of the population) reached values within the therapeutic goal. After 12, 18 and 24 months, mean Phe-level elevated significantly to initial level (869 ± 427 μmol/l; p = .311). Mean daily intake of natural protein at baseline was 32.3 ± 24.3 g per day. There was a significant decrease after 6 months (26.9 ± 18.8 g/day; p = .049) and 12 months (25.9 ± 16.2 g/day; p = .30) compared to baseline. Values at 18 months (27.5 ± 9.2 g/day; p = .26) and 24 months (35.0 ± 22.3 g/day; p = .87) did not differ. Mean daily supplementation of Phe-free amino acids was 26.2 ± 19.2 g per day. In all follow-up examinations a significant increase compared to baseline values was calculated (42.4 ± 17.6 g/day after 6 moths (p = .028), 52.1 ± 29.9 g/day after 12 months (p ≤.01), 38.7 ± 20.3 g/day after 18 months (p < .01) and 39.3 ± 21.9 g/day after 24 months (p = .014)). At baseline, mean total protein intake (natural protein plus supplements) was 0.97 ± 0.42 g per kg body weight (g/kgBW). After 24 months the protein intake was within recommended levels. (1.23 ± 0.33 g/kgKB; p = .013). After 24 months, plasma Vitamin B12 increased to 424.8 ± 176.9 pg/ml (baseline 368.6 ± 205.6 pg/ml; p = .049) and Vitamin D increased to 30.4 ± 9.9 ng/ml (baseline 24.5 ± 10.1 ng/ml; p = .06).

Conclusion

Counselling by a professional nutrionist in young adults with PKU has clear short-term effects on plasma Phe-levels. Easy applicable therapeutic recommendations, as additional intake of amino acid supplement, are well tolerated and result in strict therapy adherence up to 24 months. Apart from that, the effects on Phe-levels seem only to sustain for about 6 months. More frequent nutritional counselling, i.e. at least two times per year, is recommended to preserve positive effects on Phe-levels. Lack of Vitamin B12 and Vitamin D still are common in PKU patients, but not necessarily need to be substituted. They can effectively be equalized by a well-balanced diet within 24 months.

Case-control study about the acceptance of Pegvaliase in Phenylketonuria

Introduction

Pegvaliase is a novel enzyme substitution therapy approved by the European Drug Administration (EDA) in May 2019 for the treatment of Phenylketonuria (PKU) in adults and children ≥16 years of age. The pegylated phenylalanine ammonia lyase is isolated from bacteria and therefore provokes multifarious immunogenic reactions. Thus, the selection of the right patient for a potential harmful treatment is essential for patient's contentedness and long-term therapy compliance.

Methods and results

101 patients with PKU were screened for eligibility for an additional treatment with Pegvaliase. 51 patients were included in the study, 26 received a structural information about the new treatment for in mean 43 ± 12 min and clinical data and plasma Phe-levels were assessed. After 4 weeks of consideration the willing of treatment initiation as well as reasons for denial are registered. 7 patients (27%) concluded in beginning of treatment. Phe-level in this (acceptance) group were higher (1180 ± 231 μmol/l) compared to the denial group (930 ± 278 μmol/l, p = .01). After 4 weeks Phe-levels in the acceptance group remained stable (1264 ± 311 μmol/l, p = .26) while Phe-levels in the denial group decreased (779 ± 226 μmol/l, p < .01). Main reasons for denial of therapy were fear of adverse effects (47%), no need for additional treatment (26%) and the subcutaneous way of application (21%).

Conclusion

PKU patients have reservations against an invasive subcutaneous treatment for their disease. This is mainly caused by the form of application by syringe and the potential harmful side effects. Only less than one-third of the patients in our cohort are willing to start treatment. Besides that, most PKU patients seem to have untapped potential for self-contained reduction of Phe-levels only by being focused on their diet.