Neuropsychological outcome of subjects participating in the PKU adult collaborative study: a preliminary review

Expert Consensus on the Long-Term Effectiveness of Medical Nutrition Therapy and Its Impact on the Outcomes of Adults with Phenylketonuria

Many adults with phenylketonuria (PKU) rely on medical nutrition therapy (MNT; low phenylalanine (Phe) diet with protein substitutes/medical foods) to maintain blood Phe concentrations within recommended ranges and prevent PKU-associated comorbidities. Despite disease detection through newborn screening and introduction of MNT as early as birth, adherence to MNT often deteriorates from childhood onwards, complicating the assessment of its effectiveness in the long term. Via a modified Delphi process, consensus (≥70% agreement) was sought on 19 statements among an international, multidisciplinary 13-member expert panel. After three iterative voting rounds, the panel achieved consensus on 17 statements related to the limitations of the long-term effectiveness of MNT (7), the burden of long-term reliance on MNT (4), and its potential long-term detrimental health effects (6). According to the expert panel, the effectiveness of MNT is limited in the long term, is associated with a high treatment burden, and demonstrates that adults with PKU are often unable to achieve metabolic control through dietary management alone, creating an unmet need in the adult PKU population.

Total choline intake and working memory performance in adults with phenylketonuria

BACKGROUND

Despite early diagnosis and compliance with phenylalanine (Phe)-restricted diets, many individuals with phenylketonuria (PKU) still exhibit neurological changes and experience deficits in working memory and other executive functions. Suboptimal choline intake may contribute to these impairments, but this relationship has not been previously investigated in PKU. The objective of this study was to determine if choline intake is correlated with working memory performance, and if this relationship is modified by diagnosis and metabolic control.

METHODS

This was a cross-sectional study that included 40 adults with PKU and 40 demographically matched healthy adults. Web-based neurocognitive tests were used to assess working memory performance and 3-day dietary records were collected to evaluate nutrient intake. Recent and historical blood Phe concentrations were collected as measures of metabolic control.

RESULTS

Working memory performance was 0.32 z-scores (95% CI 0.06, 0.58) lower, on average, in participants with PKU compared to participants without PKU, and this difference was not modified by total choline intake (F[1,75] = 0.85, p = 0.36). However, in a subgroup with complete historical blood Phe data, increased total choline intake was related to improved working memory outcomes among participants with well controlled PKU (Phe = 360 µmol/L) after adjusting for intellectual ability and mid-childhood Phe concentrations (average change in working memory per 100 mg change in choline = 0.11; 95% CI 0.02, 0.20; p = 0.02). There also was a trend, albeit nonsignificant (p = 0.10), for this association to be attenuated with increased Phe concentrations.

CONCLUSIONS

Clinical monitoring of choline intake is essential for all individuals with PKU but may have important implications for working memory functioning among patients with good metabolic control. Results from this study should be confirmed in a larger controlled trial in people living with PKU.

Cognitive Functioning in Adults with Phenylketonuria in a Cohort of Spanish Patients

The early introduction of a low phenylalanine (Phe) diet has been demonstrated to be the most successful treatment in subjects with phenylketonuria (PKU), especially for preventing severe cognitive and neurological damages. However, it still concerns that even if treated in the first months of life with supplements and following a diet, they can show slight scores below people without PKU in neuropsychological assignments. We investigated 20 adults with classical PKU aged 19-48 years (mean age 29 years) and 20 heathy controls matched by age, gender, and years of education. Patients and controls were assessed with an extended neuropsychological battery, as well as psychological aspects and quality of life, also the last Phe level result was obtained. Results showed that the most affected cognitive domains are processing speed, executive functioning, memory, and also theory of mind, but very well-preserved verbal fluency, language, and visuospatial functioning. In quality of life, some significant results were seen specially in anxiety of Phe levels, anxiety of Phe levels during pregnancy, guilt if poor adherence to supplements, and if dietary protein restriction not followed. No significant results were obtained for the psychological variables. In conclusion, it has been shown that a combination of a low Phe diet, supplement intake, and keeping Phe levels in a low range seems appropriate to have the most normal and alike cognitive performance to persons without PKU.

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).

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.

Amino Acids, B Vitamins, and Choline May Independently and Collaboratively Influence the Incidence and Core Symptoms of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a developmental disorder of variable severity, characterized by difficulties in social interaction, communication, and restricted or repetitive patterns of thought and behavior. In 2018, the incidence of ASD was 2.4 times higher than estimated in 2000. Behavior and brain development abnormalities are present in the complex disorder of ASD. Nutritional status plays a key role in the incidence and severity of the core symptoms of ASD. The aim of this study was to review the available peer-reviewed studies that evaluated the relationship between amino acids, choline, B vitamins, and ASD incidence and/or severity of symptoms. Through examining plasma profiles, urine samples, and dietary intake, researchers found that low choline, abnormal amino acid, and low B vitamin levels were present in children with ASD compared to those without ASD. The evidence supports the need for future research that implements simultaneous supplementation of all essential nutrients in individuals with ASD and among prenatal mothers. Future evidence could lead to scientific breakthroughs, ultimately reducing the rates of ASD incidence and severity of symptoms by applying nutritional interventions in at-risk populations.

Mental health diagnoses in adults with phenylketonuria: a retrospective systematic audit in a large UK single centre

BACKGROUND

Recently published European Society for Phenylketonuria (ESPKU) guidelines have recommended a lifelong diet with phenylalanine (Phe) control ≤ 600 μmol/L for phenylketonuria (PKU) patients. This study aimed to identify whether PKU adult patients are at a higher risk of mental health diagnoses if their 2-year average Phe level is higher than the ESPKU European guidelines. Published studies identified by a literature review showed that related studies have been published in American and European PKU study populations but not in the United Kingdom (UK) study populations. Previous studies also involved a smaller number of participants due to this being a rare disease.

RESULTS

We undertook a retrospective audit at a single large PKU centre in the UK. 244 adult PKU patients at the centre were included, 220 of which had a recorded Phe level. Approximately 75% of the patients in this study did not meet the ESPKU European guidelines for Phe control. A systematic search of the electronic patient record was undertaken looking for mental health diagnoses. Compared to two-year average Phe levels ≤ 600 μmol/L, PKU adult patients with two-year average Phe levels > 600 μmol/L were more likely to have diagnoses of low mood, depression, anxiety, or mood swings, but only low mood reached statistical significance (p < 0.05).

CONCLUSIONS

PKU patients with two-year average Phenylalanine levels greater than ESPKU guidelines may be at greater risk of mental health diagnoses and symptoms. Many of these adult PKU patients will be lost to follow-up, and therefore may be receiving treatment for mental health conditions in the community. Multicentre UK studies and international collaborations are required to overcome low participant numbers in the study of this rare disease.

Long-term cognitive and psychosocial outcomes in adults with phenylketonuria

Previous studies have suggested that cognitive and psychosocial underfunctioning in early-treated adults with phenylketonuria (PKU) may be explained by suboptimal adherence to dietary treatments, however, these studies often employ small samples, with different outcome measures, definitions and cut-offs. Samples have also tended to comprise participants with a limited range of blood phenylalanine concentrations, and often individuals who may not have been treated early enough to avoid neurological damage. In this study, we explore the impact of lifetime dietary control, as indicated by blood phenylalanine concentrations in childhood, adolescence and adulthood, on long-term cognitive and psychosocial outcomes in a large sample of adults with PKU who were diagnosed by neonatal screening and commenced on dietary treatment within the first month of life. One hundred and fifty-four participants underwent cognitive testing, assessing attention, learning, working memory, language, executive functioning and processing speed. One hundred and forty-nine completed measures of psychosocial functioning, documenting educational, occupational, quality of life, emotional and social outcomes which were compared with a group of healthy controls. Many adults with PKU demonstrated cognitive impairments, most frequently affecting processing speed (23%), executive function (20%) and learning (12%). Cognitive outcomes were related to measures of historic metabolic control, but only processing speed was significantly related to phenylalanine concentration at the time of testing after controlling for historic levels. Adults with PKU did not, however, differ from controls in educational, occupational, quality of life or emotional outcomes, or on a measure of family functioning, and showed only minor differences in relationship style. These findings have implications for patient counselling and decisions regarding the management of PKU in adulthood.

The effect of improved dietary control on cognitive and psychiatric functioning in adults with phenylketonuria: the ReDAPT study

Background

Phenylketonuria (PKU) is an autosomal recessive inherited disorder characterised by a deficiency in phenylalanine hydroxylase. Untreated, PKU is associated with a wide range of cognitive and psychiatric sequelae. Contemporary management guidelines recommend lifetime dietary control of phenylalanine (Phe) levels, however many individuals who discontinue dietary control subsequently suffer symptoms of anxiety, depression and disturbances to cognition. We undertook a prospective cohort study of patients with early-treated phenylketonuria who had ceased dietary control to test the hypothesis that resumption of dietary control of PKU is associated with improvements in measures of psychiatric morbidity and cognitive functioning.

Methods

We re-initiated dietary control for early-treated patients with PKU and monitored cognitive and psychiatric outcomes over a twelve-month period. Assessments included objective cognitive function (measured by cognitive proficiency index (CPI)), anxiety and depression scales. General linear mixed model (GLMM) analyses were performed to assess change in psychometric variables from baseline over twelve months after resumption of dietary control.

Results

A total of nine patients were recruited. Mean age was 33 years (SD = 8.75), five were female. Mean time off dietary control was 19.1 years (SD = 11.3), and mean baseline phenylalanine (Phe) levels were 1108 µmol/L (SD = 293). GLMM analysis demonstrated a positive relationship between CPI and time on diet (b = 0.56 [95% CI = 0.17, 0.95]). Age, time off diet, Phe levels and depression scores were not associated with cognitive function. There was a negative relationship between time on diet and anxiety (b = − 0.88 95% CI = [− 1.26, − 0.50]) and depression ratings (b = − 0.61, 95% CI = [− 0.95, − 0.26]).

Conclusions

This study demonstrated improvements in cognitive function, anxiety, and depression ratings associated with resumption of dietary control of PKU. Raw Phe levels were not strongly associated with psychiatric or cognitive scores in this cohort. These findings support the importance of lifelong treatment for PKU in improving the cognitive and psychiatric sequelae of the disease.

Cognitive Outcomes and Relationships with Phenylalanine in Phenylketonuria: A Comparison between Italian and English Adult Samples

We aimed to assess if the same cognitive batteries can be used cross-nationally to monitor the effect of Phenylketonuria (PKU). We assessed whether a battery, previously used with English adults with PKU (AwPKU), was also sensitive to impairments in Italian AwPKU. From our original battery, we selected a number of tasks that comprehensively assessed visual attention, visuo-motor coordination, executive functions (particularly, reasoning, planning, and monitoring), sustained attention, and verbal and visual memory and learning. When verbal stimuli/or responses were involved, stimuli were closely matched between the two languages for psycholinguistic variables. We administered the tasks to 19 Italian AwPKU and 19 Italian matched controls and compared results from with 19 English AwPKU and 19 English matched controls selected from a previously tested cohort. Participant election was blind to cognitive performance and metabolic control, but participants were closely matched for age and education. The Italian AwPKU group had slightly worse metabolic control but showed levels of performance and patterns of impairment similar to the English AwPKU group. The Italian results also showed extensive correlations between adult cognitive measures and metabolic measures across the life span, both in terms of Phenylalanine (Phe) levels and Phe fluctuations, replicating previous results in English. These results suggest that batteries with the same and/or matched tasks can be used to assess cognitive outcomes across countries allowing results to be compared and accrued. Future studies should explore potential differences in metabolic control across countries to understand what variables make metabolic control easier to achieve.

Approaching altered inhibitory control in phenylketonuria: A functional MRI study with a Go-NoGo task in young female adults

Subtle executive function deficits, particularly regarding inhibitory control, have been reported in patients with phenylketonuria (PKU) despite early dietary treatment. Purpose of this study was to assess whether young female adults with PKU exhibit altered neural activity underlying such deficits, particularly in a fronto-parietal cognitive control network (CCN). Behavioural data and functional magnetic resonance imaging (fMRI) data were acquired during a Go-NoGo task in 16 young adult patients with PKU and 17 control subjects. Hypothesis-driven analyses of behavioural and fMRI data in the CCN were supplemented by exploratory whole brain activation analyses. PKU patients exhibited a trend towards higher errors of commission. Patients exhibited marginally increased activation associated with inhibitory control in only one CCN core region (right middle frontal gyrus, p = .043). Whole brain analyses revealed widespread relatively increased activation in adults with PKU in the main task contrast (NoGo > Go). This increased activation was mainly observed outside the CCN and largely overlapped with the default mode network (DMN). In conclusion, only subtle inhibitory control deficits and associated brain activity differences were observed in young adults with PKU. Thus, this work adds to the notion that this particular population seems to be only slightly affected by such cognitive deficits. While there were also only minimal increases when compared to healthy subjects in brain activity in a cognitive control network, we observed more widespread activation increases outside this network. These results support the assumption of DMN dysfunction in PKU.

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.

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.

Neurocognitive functioning in adults with phenylketonuria: Report of a 10-year follow-up

BACKGROUND

The long-term prognosis of early treated phenylketonuria (PKU) is still under discussion. Aim of this controlled long-term study was to assess the neurological and neuropsychological outcome in adult patients with early-treated PKU.

METHODS

We investigated 35 patients with early-treated classical PKU aged 29 to 51 years (mean age 41 years) and 18 healthy controls matched for age and socioeconomic status. Patients and controls were assessed for their intelligence quotient (IQ), attention and information-processing abilities. Magnetic resonance imaging (MRI) of the brain was performed in all patients. Neuropsychological assessments and MRI were repeated at a five-year and a ten-year follow-up.

RESULTS

In the entire interval IQ, information processing and attention of patients and controls remained constant. At both follow-up assessment times the IQ scores were significantly lower in patients compared to controls. Older adult patients (> 42 years) showed poorer information processing and attention at both assessment times compared to young adult patients (< 42 years) and controls. IQ, information processing and attention showed no correlation to imaging results. IQ, however, was significantly correlated to blood phenylalanine (Phe) levels in patients´ childhood and adolescence, and Phe levels had been higher in the adolescent years of older adult patients.

CONCLUSIONS

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

The neurological and psychological phenotype of adult patients with early-treated phenylketonuria: A systematic review

Newborn screening for phenylketonuria (PKU) and early introduction of dietary therapy has been remarkably successful in preventing the severe neurological features of PKU, including mental retardation and epilepsy. However, concerns remain that long-term outcome is still suboptimal, particularly in adult patients who are no longer on strict phenylalanine-restricted diets. With our systematic literature review we aimed to describe the neurological phenotype of adults with early-treated phenylketonuria (ETPKU). The literature search covered the period from 1 January 1990 up to 16 April 2018, using the NLM MEDLINE controlled vocabulary. Of the 643 records initially identified, 83 were included in the analysis. The most commonly reported neurological signs were tremor and hyperreflexia. The overall quality of life (QoL) of ETPKU adults was good or comparable to control populations, and there was no evidence for a significant incidence of psychiatric disease or social difficulties. Neuroimaging revealed that brain abnormalities are present in ETPKU adults, but their clinical significance remains unclear. Generally, intelligence quotient (IQ) appears normal but specific deficits in neuropsychological and social functioning were reported in early-treated adults compared with healthy individuals. However, accurately defining the prevalence of these deficits is complicated by the lack of standardized neuropsychological tests. Future research should employ standardized neurological, neuropsychological, and neuroimaging protocols, and consider other techniques such as advanced imaging analyses and the recently validated PKU-specific QoL questionnaire, to precisely define the nature of the impairments within the adult ETPKU population and how these relate to metabolic control throughout life.

Determinants of Plasma Docosahexaenoic Acid Levels and Their Relationship to Neurological and Cognitive Functions in PKU Patients: A Double Blind Randomized Supplementation Study

Children with phenylketonuria (PKU) follow a protein restricted diet with negligible amounts of docosahexaenoic acid (DHA). Low DHA intakes might explain subtle neurological deficits in PKU. We studied whether a DHA supply modified plasma DHA and neurological and intellectual functioning in PKU. In a double-blind multicentric trial, 109 PKU patients were randomized to DHA doses from 0 to 7 mg/kg&amp;day for six months. Before and after supplementation, we determined plasma fatty acid concentrations, latencies of visually evoked potentials, fine and gross motor behavior, and IQ. Fatty acid desaturase genotypes were also determined. DHA supplementation increased plasma glycerophospholipid DHA proportional to dose by 0.4% DHA per 1 mg intake/kg bodyweight. Functional outcomes were not associated with DHA status before and after intervention and remained unchanged by supplementation. Genotypes were associated with plasma arachidonic acid levels and, if considered together with the levels of the precursor alpha-linolenic acid, also with DHA. Functional outcomes and supplementation effects were not significantly associated with genotype. DHA intakes up to 7 mg/kg did not improve neurological functions in PKU children. Nervous tissues may be less prone to low DHA levels after infancy, or higher doses might be required to impact neurological functions. In situations of minimal dietary DHA, endogenous synthesis of DHA from alpha-linolenic acid could relevantly contribute to DHA status.

A systematic review of cognitive functioning in early treated adults with phenylketonuria

BACKGROUND

Even though early dietary management of phenylketonuria (PKU) successfully prevents severe neurological impairments, deficits in cognitive functioning are still observed. These deficits are believed to be the result of elevated levels of phenylalanine throughout life. Research on cognitive functioning in adults with PKU (AwPKU) often focuses on domains shown to be compromised in children with PKU, such as attention and executive functions, whereas other cognitive domains have received less attention. This systematic review aimed to provide an overview of cognitive functioning across domains examined in early treated (ET) AwPKU.

METHODS

A systematic search was performed in Ovid MEDLINE(R), PsycINFO, Web of Science, Cochrane, Scopus, Embase, ScienceDirect, and PubMed for observational studies on cognitive performance in ET AwPKU.

RESULTS

Twenty-two peer-reviewed publications, reporting on outcomes from 16 studies were reviewed. Collectively, the results most consistently showed deficits in vigilance, working memory and motor skills. Deficits in other cognitive domains were less consistently observed or were understudied. Furthermore, despite reports of several associations between cognitive performance and phenylalanine (Phe) levels throughout life the relationship remains unclear. Inconsistencies in findings across studies could be explained by the highly heterogeneous nature of study samples, resulting in large inter- and intra-variability in Phe levels, as well as the use of a variety of tests across cognitive domains, which differ in sensitivity. The long-term cognitive outcomes of early and continuous management of PKU remain unclear.

CONCLUSIONS

To better understand the development of cognitive deficits in ET AwPKU, future research would benefit from 1) (inter)national multicentre-studies; 2) more homogeneous study samples; 3) the inclusion of other nutritional measures that might influence cognitive functioning (e.g. Phe fluctuations, Phe:Tyrosine ratio and micronutrients such as vitamin B12); and 4) careful selection of appropriate cognitive tests.

Salivary serotonin does not correlate with central serotonin turnover in adult phenylketonuria (PKU) patients

INTRODUCTION

Phenylketonuria (PKU) is an inborn error of metabolism associated with an increased risk of behavioural and mood disorders. There are currently no reliable markers for monitoring mood in PKU. The purpose of this study was to evaluate salivary serotonin as a possible non-invasive marker of long-term mood symptoms and central serotonin activity in patients with PKU.

METHODS

20 patients were recruited from our Adult Metabolic Diseases Clinic. Age, sex, plasma phenylalanine (Phe) level, DASS (Depression Anxiety Stress Scales) depression score, DASS anxiety score, BMI, salivary serotonin, salivary cortisol, 2-year average Phe, 2-year average tyrosine (Tyr), and 2-year average Phe:Tyr ratio were collected for each patient. Spearman's ρ correlation analysis was used to determine if there was any relationship between any of the parameters.

RESULTS

There were positive correlations between DASS anxiety and DASS depression scores (Spearman's ρ = 0.8708, p-value < 0.0001), BMI and plasma Phe level (Spearman's ρ = 0.6228, p-value = .0034), and 2-year average Phe and BMI (Spearman's ρ = 0.5448, p-value = .0130). There was also a negative correlation between salivary cortisol and plasma Phe level (Spearman's ρ = -0.5018, p-value = .0338). All other correlations were not statistically significant.

CONCLUSION

Salivary serotonin does not correlate with peripheral phenylalanine levels, DASS depression scale scores, or DASS anxiety scale scores, implying that salivary serotonin does not reflect central serotonin turnover. Additionally, this study suggests that salivary serotonin is not a suitable marker for monitoring dietary control, mood, or anxiety in PKU.

SYNOPSIS

Salivary serotonin does not correlate with peripheral phenylalanine levels, DASS depression scale scores, or DASS anxiety scale scores, suggesting that salivary serotonin is not a suitable marker for monitoring dietary control, mood, or anxiety in PKU.

Developmental Trajectories of Executive and Verbal Processes in Children with Phenylketonuria

Phenylketonuria (PKU) is a hereditary disorder characterized by disrupted phenylalanine metabolism and cognitive impairment. However, the precise nature and developmental trajectory of this cognitive impairment remains unclear. The present study used a verbal fluency task to dissociate executive and verbal processes in children with PKU (n = 23; 7-18 years) and controls (n = 44; 7-19 years). Data were collected at three longitudinal timepoints over a three-year period, and the contributions of age, group, and their interaction to fluency performance were evaluated. Results indicated impairments in executive processes in children with PKU, which were exacerbated by declining metabolic control.

The impact of phenylalanine levels on cognitive outcomes in adults with phenylketonuria: Effects across tasks and developmental stages

Objective: Phenylketonuria (PKU) is due to an inability to metabolize the amino acid phenylalanine (Phe), leading to its accumulation in the brain. Phe levels can be controlled following a protein-free diet, but cognitive impairments are still present. A number of questions remain to be answered related to which type of metabolic control is important, the age when it is important, the cognitive functions which are most affected and, the best tests to use to monitor cognitive health. Method: We investigated the impact of metabolic control at different ages on cognitive performance in 37 early treated adults with PKU. Results: (a) Phe variation was as associated to performance as average Phe showing that stable dietary control is as important as strict control; (b) For some tasks, current and adult Phe were stronger predictors of performance than childhood or adolescent Phe, showing the importance of a strict diet even in adulthood; and (c) The relationship between performance and Phe levels varied depending on time and cognitive domain. For some functions (sustained attention, visuomotor coordination), Phe at the time of testing was the best predictor. While for other functions (visual attention, executive functions) there was a diminishing or stable relationship across time. Conclusion: Results show the importance of selecting the right tasks to monitor outcomes across ages, but also that the impact of bio-chemical disruptions is different for different functions, at different ages. We show how inherited metabolic diseases offer us a unique vantage point to inform our understanding of brain development and functioning.

Speed of processing and executive functions in adults with phenylketonuria: Quick in finding the word, but not the ladybird

A reduction in processing speed is widely reported in phenylketonuria (PKU), possibly due to white matter pathology. We investigated possible deficits and their relationships with executive functions in a sample of 37 early-treated adults with PKU (AwPKUs). AwPKUs were not characterized by a generalized speed deficit, but instead their performance could be explained by two more specific impairments: (a) a deficit in the allocation of visuo-spatial attention that reduced speed in visual search tasks, in some reading conditions and visuo-motor coordination tasks; and (b) a more conservative decision mechanism that slowed down returning an answer across domains. These results suggest that the impairments in executive functions seen in AwPKUs are not the consequence of a generalized speed deficit. They also suggest that processing speed is linked to the efficiency of a particular cognitive component and cannot be considered a general function spanning domains. Similarities with patterns in ageing are discussed.

Host conditioning and rejection monitoring in hepatocyte transplantation in humans

BACKGROUND & AIMS

Hepatocyte transplantation partially corrects genetic disorders and has been associated anecdotally with reversal of acute liver failure. Monitoring for graft function and rejection has been difficult, and has contributed to limited graft survival. Here we aimed to use preparative liver-directed radiation therapy, and continuous monitoring for possible rejection in an attempt to overcome these limitations.

METHODS

Preparative hepatic irradiation was examined in non-human primates as a strategy to improve engraftment of donor hepatocytes, and was then applied in human subjects. T cell immune monitoring was also examined in human subjects to assess adequacy of immunosuppression.

RESULTS

Porcine hepatocyte transplants engrafted and expanded to comprise up to 15% of irradiated segments in immunosuppressed monkeys preconditioned with 10Gy liver-directed irradiation. Two patients with urea cycle deficiencies had early graft loss following hepatocyte transplantation; retrospective immune monitoring suggested the need for additional immunosuppression. Preparative radiation, anti-lymphocyte induction, and frequent immune monitoring were instituted for hepatocyte transplantation in a 27year old female with classical phenylketonuria. Post-transplant liver biopsies demonstrated multiple small clusters of transplanted cells, multiple mitoses, and Ki67+ hepatocytes. Mean peripheral blood phenylalanine (PHE) level fell from pre-transplant levels of 1343±48μM (normal 30-119μM) to 854±25μM (treatment goal ≤360μM) after transplant (36% decrease; p<0.0001), despite transplantation of only half the target number of donor hepatocytes. PHE levels remained below 900μM during supervised follow-up, but graft loss occurred after follow-up became inconsistent.

CONCLUSIONS

Radiation preconditioning and serial rejection risk assessment may produce better engraftment and long-term survival of transplanted hepatocytes. Hepatocyte xenografts engraft for a period of months in non-human primates and may provide effective therapy for patients with acute liver failure.

LAY SUMMARY

Hepatocyte transplantation can potentially be used to treat genetic liver disorders but its application in clinical practice has been impeded by inefficient hepatocyte engraftment and the inability to monitor rejection of transplanted liver cells. In this study, we first show in non-human primates that pretreatment of the host liver with radiation improves the engraftment of transplanted liver cells. We then used this knowledge in a series of clinical hepatocyte transplants in patients with genetic liver disorders to show that radiation pretreatment and rejection risk monitoring are safe and, if optimized, could improve engraftment and long-term survival of transplanted hepatocytes in patients.

Subtle visuomotor deficits and reduced benefit from practice in early treated phenylketonuria

INTRODUCTION

Phenylketonuria (PKU) is a rare metabolic disease that causes slight-to-severe neurological symptoms. Slow performance has been observed in PKU but the influence of high-order (i.e., not purely motor) deficits and of temporary variations of the phenylalanine (Phe) level on this slowness has not been fully corroborated as yet. Response speed and the effect of motor practice during the performance of a visuomotor coordination task were measured, in a group of patients with early-treated phenylketonuria (ET PKU).

METHOD

We compared the performance of a group of early-treated PKU patients with ages ranging from 11 to 25 years and a control group of healthy volunteers on a computerized visuomotor task. Participants performed rapid movements towards one of five response buttons, as indicated by a visual stimulus that could appear in five different positions on a computer screen. The results of our visuomotor task were correlated with neurobiological data (Phe levels) and with neuropsychological measures of motor (finger tapping) and executive functions (Stroop task).

RESULTS

The ET PKU group showed slower responses than the control group. Furthermore, an absence of a practice effect (i.e., faster response times at the end of the study) was found in the PKU group but not in the control group. Our results also revealed that this absence of practice effect correlated with higher Phe levels on the testing day with respect to the average Phe level of the previous 12 months and, although weakly, with performance on the Stroop task.

CONCLUSIONS

This pattern of results indicates slower visuomotor performance and a less beneficial effect of practice in ET PKU. The correlations found among our visuomotor measures, the same-day Phe level, and the Stroop test may reflect the negative effects of dopamine reduction in brain areas involved in motor control, selective attention, and learning.

Cognitive outcomes in early-treated adults with phenylketonuria (PKU): A comprehensive picture across domains

OBJECTIVE

Phenylketonuria (PKU) is an inherited metabolic disease which affects cognitive functions due to an inability to metabolize phenylalanine which leads to the accumulation of toxic by-products (Phe) in the brain. PKU can be effectively treated with a low phenylalanine diet, but some cognitive deficits remain. Studies have reported impairments, especially for processing speed and executive functions, but there is a lack of comprehensive assessment across cognitive domains. Moreover, it is important to establish outcomes in early treated adults with PKU (AwPKU) who have better metabolic control than groups previously reported in the literature.

METHOD

We tested 37 AwPKU with an unprecedented number of tasks (N = 28) and measures (N = 44) and compared results with 30 controls matched for age and education.

RESULTS

We found (a) group impairments, particularly in tasks tapping speed of processing and complex executive functions; (b) high variability across participants, with a sizable number of AwPKU with completely normal performance (about 38%); (c) but also a sizable number of participants who were clearly impaired (about 24%); and (d) good performance in tasks tapping verbal learning, verbal memory and orthographic processing, indicating no generalized learning impairment.

CONCLUSION

Our results indicate good outcomes, but also that deficits are still present with current treatment policies. (PsycINFO Database Record

Systematic Review and Meta-Analysis of Neuropsychiatric Symptoms and Executive Functioning in Adults With Phenylketonuria

This systematic review and meta-analysis (MA) investigates the impact of elevated blood phenylalanine (Phe) on neuropsychiatric symptoms in adults with phenylketonuria (PKU). The meta-analysis of PKU is challenging because high-quality evidence is lacking due to the limited number of affected individuals and few placebo-controlled, double-blind studies of adults with high and low blood Phe. Neuropsychiatric symptoms associated with PKU exceed general population estimates for inattention, hyperactivity, depression, and anxiety. High Phe is associated with an increased prevalence of neuropsychiatric symptoms and executive functioning deficits whereas low Phe is associated with improved neurological performance. Findings support lifelong maintenance of low blood Phe.

Autism in Phenylketonuria Patients: From Clinical Presentation to Molecular Defects

Autism has been reported in untreated patients with phenylketonuria. The authors aimed to explore autism in 15 Tunisian and 4 Algerian phenylketonuria patients, and report their clinical, biochemical and molecular peculiarities. The Childhood Autism Rating Scale and the Autism Diagnostic Interview-Revised were used for the diagnosis of autism. Five exons of phenylalanine hydroxylase gene (7, 6, 10, 11, and 5) were amplified by polymerase chain reaction and directly sequenced. Among these patients, 15 were suffering from autism at the time of evaluation. Six mutations were identified: p.E280K, p.G352Vfs, IVS10nt11, p.I224T, p.R261Q, and p.R252W. There was no correlation between autism and mutations affecting the phenylalanine hydroxylase gene, but the age of diet onset was the determining factor in autistic symptoms' evolution.

Psychiatric disorders in adolescent and young adult patients with phenylketonuria

BACKGROUND AND OBJECTIVES

Psychiatric symptoms are a challenging aspect in adolescent and adult early treated phenylketonuric (ETPKU) patients. To assess the occurrence of psychiatric disorders we explored the presence of symptoms requiring intervention and further investigated the link between psychiatric disorders, the quality of biochemical control and cognitive functioning.

PATIENTS AND METHODS

Forty-six ETPKU patients (aged 12 to 44) and 30 age-matched healthy controls were subjected to cognitive and psychiatric assessment by means of self-report questionnaires and psychiatric interview. Psychiatric diagnoses, if detected, were made according to DSM-5 criteria. Concomitant IQ, historical and concurrent biochemical metabolic controls were included in the statistical analysis.

RESULTS

Twenty-five out of 46 ETPKUs showed clinical scores on at least one scale of the psychiatric assessment (7/30 in controls); anxiety and withdrawal were the most frequent self-reported symptoms. Seventeen patients (and no controls) met criteria for a psychiatric diagnosis, most of them belonging to the Anxiety Disorders category. The occurrence of psychiatric symptoms was not associated with the life-long and concurrent quality of metabolic control but patients with good metabolic control (≤ 500 μM) in the first 11 years of life showed higher frequency of psychiatric diagnosis (Fisher's exact p=.0300).

DISCUSSION/CONCLUSION

ETPKUs show a higher than normal vulnerability to psychiatric disorders, which cannot be explained by the usual biochemical alterations influencing intellectual outcome. Our data support the hypothesis that the burden of the disease acts as psychological stress for children and their families. Possible involvement of neuromediators in the pathogenesis of these complex symptoms requires further investigation.

ADHD, autism and neuroradiological complications among phenylketonuric children in Upper Egypt

The aim of this study is to evaluate the neuropsychological status in a cohort of children with early and continuously treated phenylketonuria in Assiut, Upper Egypt. The study was implemented in seventy-eight phenylketonuria (PKU) children. Only 34 patients met the inclusion criteria. Investigated patients were evaluated according to detailed history, neurological examination, Childhood Autism Rating Scale, full scale Intelligence Quotient, attention deficit hyperactivity disorder, electroencephalography and magnetic resonance imaging (MRI). This study concluded that the prognosis for early diagnosed children with PKU treated from the first weeks of life is generally good. However, they are at increased risk for neurological complications and behavioral problems. So, neonatal screening for PKU is highly recommended in Egypt, for early detection and management. In addition, neuropsychological and MRI assessments in PKU children should be done.

Phenylketonuria: a review of current and future treatments

Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism caused by a deficiency in the hepatic enzyme phenylalanine hydroxylase (PAH). If left untreated, the main clinical feature is intellectual disability. Treatment, which includes a low Phe diet supplemented with amino acid formulas, commences soon after diagnosis within the first weeks of life. Although dietary treatment has been successful in preventing intellectual disability in early treated PKU patients, there are major issues with dietary compliance due to palatability of the diet. Other potential issues associated with dietary therapy include nutritional deficiencies especially vitamin D and B12. Suboptimal outcomes in cognitive and executive functioning have been reported in patients who adhere poorly to dietary therapy. There have been continuous attempts at improving the quality of medical foods including their palatability. Advances in dietary therapy such as the use of large neutral amino acids (LNAA) and glycomacropeptides (GMP; found within the whey fraction of bovine milk) have been explored. Gene therapy and enzyme replacement or substitution therapy have yielded more promising data in the recent years. In this review the current and possible future treatments for PKU are discussed.

Inherited Metabolic Disorders: Aspects of Chronic Nutrition Management

The introduction of newborn screening and the development of new therapies have led to an expanding population of patients with inherited metabolic disorders, and these patients are now entering adulthood. Dietary therapy is the mainstay of treatment for many of these disorders, and thus, trained metabolic dietitians are critical members of the multidisciplinary team required for management of such patients. The main goals of dietary therapy in inborn errors of metabolism are the maintenance of normal growth and development while limiting offending metabolites and providing deficient products. Typically, the offending metabolite is either significantly reduced or removed completely from the diet and then reintroduced in small quantities until blood levels are within the normal range. Such treatment is required in infancy, childhood, and adulthood and requires careful monitoring of micronutrient and macronutrient intake throughout the life span. The goal of this review is to highlight the basic principles of chronic nutrition management of the inborn errors of protein, carbohydrate, and fat metabolism.

Long-term developmental progression in infants and young children taking sapropterin for phenylketonuria: a two-year analysis of safety and efficacy

PURPOSE

Sapropterin is an oral synthetic formulation of tetrahydrobiopterin prescribed as adjunctive therapy for phenylketonuria. The efficacy of sapropterin in reducing blood phenylalanine levels has been demonstrated in clinical studies of individuals with phenylketonuria older than 4 years of age. Its effect on neurocognitive functioning in younger children has not been examined.

METHODS

A 2-year interim analysis of blood phenylalanine levels, prescribed dietary phenylalanine intake, and neurocognitive functioning was performed in children who started receiving sapropterin at 0-6 years of age and responded with a ≥30% mean blood phenylalanine reduction. Children were evaluated at baseline and 2-year follow-up.

RESULTS

Sapropterin had a favorable safety profile and lowered blood phenylalanine levels with increased prescribed dietary phenylalanine intakes. Mean full-scale intelligence quotient was 103 ± 12 at baseline and 104 ± 10 at 2-year follow-up (P = 0.50, paired t-test, n = 25). For children younger than 30 months of age, the cognitive composite score from the Bayley Scales of Infant and Toddler Development, Third Edition, remained within the average range.

CONCLUSION

Sapropterin had a favorable safety profile, was effective in lowering blood phenylalanine levels while clinically requiring dietary adjustment, resulting in increased phenylalanine intake, and preserved neurocognitive performance in children who started therapy between 0 and 6 years of age.

Maternal Phenylketonuria: Long-term Outcomes in Offspring and Post-pregnancy Maternal Characteristics

Maternal phenylketonuria (MPKU) is a well-recognized complication of PKU and one of the most potent teratogenic syndromes of pregnancy. Virtually all offspring from untreated pregnancies in women with classic PKU have intellectual disabilities and microcephaly. Congenital heart disease and intrauterine growth retardation occur many times more often than expected in the general population. Control of maternal blood phenylalanine during pregnancy prevents most if not all of these complications. Previous studies demonstrated the benefits of treatment in terms of birth parameters and early development. In this study, physical examinations, a medical history, and neuropsychological evaluation were obtained in 47 children from 24 mothers with PKU who received treatment during pregnancy. Mothers were interviewed and administered an abbreviated IQ test. Associations between maternal factors and offspring outcomes were also analyzed.The 21 male and 26 female offspring ranged in age from 1 month to 26 years with 21 (62%) over 6 years. Results indicated mean intercanthal distances above the 70th percentile. Microcephaly was present in 19% of offspring, with head circumference below the third percentile. None of the offspring had cardiac anomalies. Mean offspring IQ was 94 ± 19, with 12% performing in the range of intellectual disability (IQ < 70). Among children >5 years of age, 25% had learning disabilities, 31% had attention deficit hyperactivity disorder (ADHD), 22% were on ADHD medication, and 34% had a diagnosis of anxiety and/or depression. Among the 24 mothers, 12 reported following the diet for PKU. Only one woman on diet had a blood phenylalanine concentration <360 μmol/L (recommended range) and the majority had indications of poor nutritional status. Mean maternal Full Scale IQ was 94 ± 16 (range = 61-117), with 25% performing in the borderline intellectual range (IQ < 85). Verbal IQ was significantly lower than Performance IQ (p = 0.01, CI 2.7, 16.1). On the self-report Beck Depression Inventory, Second Edition, 25% received scores indicating mild to moderate depression, and on the Beck Anxiety Inventory, 46% reported mild to moderate anxiety. Offspring IQ correlated with maternal metabolic control during pregnancy (r = 0.51), maternal IQ (r = -0.62), and socioeconomic position (r = -0.48). Offspring with ADHD, learning disabilities, or emotional disturbances were more likely to have mothers with anxiety and/or depression. To ensure optimal offspring outcomes, healthcare providers need to assess maternal nutrition, blood phenylalanine concentrations, cognitive abilities, and socioeconomic position. Interventions can then be initiated that reduce psychosocial stressors and enhance adherence to diet and positive parenting, which in turn can lead to better cognitive functioning, behavior, and emotional well-being in their children.

Variability in phenylalanine control predicts IQ and executive abilities in children with phenylketonuria

A number of studies have revealed significant relationships between cognitive performance and average phenylalanine (Phe) levels in children with phenylketonuria (PKU), but only a few studies have been conducted to examine the relationships between cognitive performance and variability (fluctuations) in Phe levels. In the current study, we examined a variety of indices of Phe control to determine which index best predicted IQ and executive abilities in 47 school-age children with early- and continuously-treated PKU. Indices of Phe control were mean Phe, the index of dietary control, change in Phe with age, and several indices of variability in Phe (standard deviation, standard error of estimate, and percentage of spikes). These indices were computed over the lifetime and during 3 developmental epochs (<5, 5.0-9.9, and ≥10 years of age). Results indicated that variability in Phe was generally a stronger predictor of cognitive performance than other indices of Phe control. In addition, executive performance was better predicted by variability in Phe during older than younger developmental epochs. These results indicate that variability in Phe should be carefully controlled to maximize cognitive outcomes and that Phe control should not be liberalized as children with PKU age.

Behavioral and neurochemical characterization of new mouse model of hyperphenylalaninemia

Hyperphenylalaninemia (HPA) refers to all clinical conditions characterized by increased amounts of phenylalanine (PHE) in blood and other tissues. According to their blood PHE concentrations under a free diet, hyperphenylalaninemic patients are commonly classified into phenotypic subtypes: classical phenylketonuria (PKU) (PHE > 1200 µM/L), mild PKU (PHE 600-1200 µM/L) and persistent HPA (PHE 120-600 µM/L) (normal blood PHE < 120 µM/L). The current treatment for hyperphenylalaninemic patients is aimed to keep blood PHE levels within the safe range of 120-360 µM/L through a PHE-restricted diet, difficult to achieve. If untreated, classical PKU presents variable neurological and mental impairment. However, even mildly elevated blood PHE levels, due to a bad compliance to dietary treatment, produce cognitive deficits involving the prefrontal cortical areas, extremely sensible to PHE-induced disturbances. The development of animal models of different degrees of HPA is a useful tool for identifying the metabolic mechanisms underlying cognitive deficits induced by PHE. In this paper we analyzed the behavioral and biochemical phenotypes of different forms of HPA (control, mild-HPA, mild-PKU and classic-PKU), developed on the base of plasma PHE concentrations. Our results demonstrated that mice with different forms of HPA present different phenotypes, characterized by increasing severity of behavioral symptoms and brain aminergic deficits moving from mild HPA to classical PKU forms. In addition, our data identify preFrontal cortex and amygdala as the most affected brain areas and confirm the highest susceptibility of brain serotonin metabolism to mildly elevated blood PHE.

Newborn screening 50 years later: access issues faced by adults with PKU

Fifty years after the implementation of universal newborn screening programs for phenylketonuria, the first disease identified through newborn screening and considered a success story of newborn screening, a cohort of adults with phenylketonuria treated from birth provides valuable information about effects of long-term treatment for inborn errors of metabolism in general, and phenylketonuria specifically. For phenylketonuria, newborn screening allows early implementation of the phenylalanine-restricted diet, eliminating the severe neurocognitive and neuromotor impairment associated with untreated phenylketonuria. However, executive function impairments and psychiatric problems are frequently reported even for those treated early and continuously with the phenylalanine-restricted diet alone. Moreover, a large percentage of adults with phenylketonuria are reported as lost to follow-up by metabolic clinics. While a group of experts identified by the National Institutes of Health convenes to update treatment guidelines for phenylketonuria, we explore individual patient, social, and economic factors preventing >70% of adult phenylketonuria patients in the United States from accessing treatment. As more conditions are identified through newborn screening, factors affecting access to treatment grow in importance, and we must continue to be vigilant in assessing and addressing factors that affect patient treatment outcomes and not just celebrate amelioration of the most severe manifestations of disease.

Developmental and psychiatric presentations of inherited metabolic disorders

Pediatric neurologists and developmental pediatricians may evaluate patients with primary or associated behavioral and academic concerns. A critical element of the evaluation involves determining that the child's condition is not better explained by underlying inherited metabolic disorders. In this review, psychiatric and behavioral presentations of inherited metabolic disorders are discussed via several case studies. Key features of vignettes will illustrate when to consider these disorders in evaluating children referred for psychiatric and behavioral changes, after more common etiologies have been excluded. We seek to develop a better understanding of key clinical pearls to help identify children with an inherited metabolic disorder to account for behavioral or academic concerns.

A diversified approach for PKU treatment: routine screening yields high incidence of psychiatric distress in phenylketonuria clinics

OBJECTIVES

Individuals with phenylketonuria (PKU) treated early and continuously are reported to have psychiatric and executive function impairments. The feasibility of screening for psychiatric distress and executive function impairment in individuals with PKU was tested in 3 separate clinics in North America.

METHODS

Individuals were offered screening for psychiatric distress using the Pediatric Symptom Checklist, the PSC-Youth Report or the Brief Symptom Inventory and executive function impairment using the Behavior Rating Inventory of Executive Function. Gender, age and blood phenylalanine (Phe) concentrations obtained most recently and during the 2 years prior to screening were assessed.

RESULTS

More than 90% of patients with PKU accepted the screening for psychiatric distress during their routine clinic visit. The screening took 15-20 min. 32% of patients screened positive for psychiatric distress and 19% for executive function impairment. More individuals >18 years screened positive for psychiatric distress while a similar number screened positive for executive function impairment across age groups. Lower blood Phe levels correlated with negative screening for psychiatric distress. Patients positive for psychiatric distress had higher (p=0.009) median and most recent blood Phe values (p=0.05).

DISCUSSION/CONCLUSIONS

Routine screening for psychiatric distress of patients with phenylketonuria could be easily implemented in current clinic structures. High incidences of positive screens reinforce the need for regular psychiatric assessments of individuals with PKU. Identification and referral to local mental health providers might help to improve the standard of care for individuals with PKU.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pilot study on executive function and adaptive skills in adolescents and young adults with mitochondrial disease

High-functioning adolescents and young adults with mitochondrial disease are now attempting transitions to postsecondary environments. This pilot and case study explores factors that interfere with their successful transition through behavior-rating scales addressing academic skills and behavior. In the Behavior Assessment System for Children, Second Edition, Spearman correlation matrices showed that students' attitude to school was associated with depression and anxiety. Mothers' reports linked internalizing disorders with somatic symptoms. Two case studies, with Behavior Rating Inventory of Executive Function profiles, show the role executive functions play in academic success. Attention to both cognitive and psychiatric concerns may increase success in academics and enhance the sense of well-being in older students with mitochondrial disease.

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 randomized, placebo-controlled, double-blind trial of supplemental docosahexaenoic acid on cognitive processing speed and executive function in females of reproductive age with phenylketonuria: A pilot study

Low blood docosahexaenoic acid (DHA) is reported in patients with phenylketonuria (PKU); however, the functional implications in adolescents and adults are unknown. This pilot study investigated the effect of supplemental DHA on cognitive performance in 33 females with PKU ages 12-47 years. Participants were randomly assigned to receive DHA (10mg/kg/day) or placebo for 4.5 months. Performance on cognitive processing speed and executive functioning tasks was evaluated at baseline and follow up. Intention-to-treat and per protocol analyses were performed. At follow up, biomarkers of DHA status were significantly higher in the DHA-supplemented group. Performance on the cognitive tasks and reported treatment-related adverse events did not differ. While no evidence of cognitive effect was seen, a larger sample size is needed to be conclusive, which may not be feasible in this population. Supplementation was a safe and effective way to increase biomarkers of DHA status (www.clinicaltrials.gov; Identifier: NCT00892554).

Using change in plasma phenylalanine concentrations and ability to liberalize diet to classify responsiveness to tetrahydrobiopterin therapy in patients with phenylketonuria

Tetrahydrobiopterin (BH(4)) responsiveness is currently defined as a decrease in plasma phenylalanine concentrations in patients with phenylketonuria (PKU). This definition does not offer insight beyond the initial assessment of patients, which may lead to treatment ambiguity in patients who only experience an initial decrease in plasma phenylalanine concentrations. We present our experience with a novel classification approach using sequentially-applied criteria. Plasma phenylalanine concentrations were measured at baseline and after one month of BH(4) therapy (20 mg/kg/day) in 58 PKU patients (34 M, 24 F; age 17.3±11.0 years). Thirty-two patients (55.2%) were classified as "preliminary responders" at one month, experiencing at least a 15% decrease in plasma phenylalanine concentrations. Preliminary responders' ability to liberalize their dietary restrictions was then systematically assessed. "Definitive responders" were defined as preliminary responders who could increase their dietary phenylalanine tolerance by at least 300 mg/day and lower prescribed medical food needs by at least 25% while maintaining metabolic control (plasma phenylalanine ≤360 μmol/L) and consuming adequate dietary protein. Preliminary responders who could not liberalize their diets according to these criteria were classified as "provisional responders." Nineteen patients (32.8% of patients initiating BH(4) therapy) met the definitive responder criteria, increasing dietary phenylalanine tolerance from 704±518 mg/day to 1922±612 mg/day and reducing medical food to 16.7±19.5% of their baseline prescription. Nine patients (15.5% of patients initiating BH(4) therapy) were classified as provisional responders, all remaining on 100% of their baseline medical food prescription. From this classification approach, a subgroup of provisionally responsive patients emerged who experienced an initial decrease in plasma phenylalanine concentrations but who could not substantially increase their dietary phenylalanine tolerance or decrease medical food needs. Diet liberalization is an essential component of BH(4)-responsiveness classification.

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

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

Mental and motor development and psychosocial adjustment of Chinese children with phenylketonuria

AIM

This study was designed to evaluate mental and motor development, psychosocial adjustment (temperament and behavioural problems) in children with phenylketonuria (PKU).

METHODS

Twenty-eight Chinese children aged from three to 36 months with early-treated PKU were evaluated by Bayley Scales of Infant Development (BSID), Peabody Developmental Motor Scale (PDMS-II), Toddler Temperament Questionnaire (TTQ) and Achenbach's Child Behavior Checklist (CBCL). The related factors, including blood phenylalanine (Phe) levels, and the socio-economic status (SES) of the children's family were also explored.

RESULTS

In comparison with healthy control, early-treated PKU children showed no delay in the mental and motor development. However, they presented higher levels on four of the nine temperamental dimensions (higher level in activity, more intense in reaction, more negative mood and more distraction). They also had more behavioural problems in depression, aggression and destructibility. A lower Phe level and a higher SES of children's family showed a positive effect on development index, temperamental characteristics and behavioural problems.

CONCLUSION

Early-treated PKU children were normal in the mental and motor development. However, they presented higher level on four of the nine temperamental dimensions and had more behavioural problems. Paediatric control combined with psycho-counselling was suggested for young PKU children.

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.

Retrospective, observational data collection of the treatment of phenylketonuria in the UK, and associated clinical and health outcomes

OBJECTIVE

To determine the percentage of phenylketonuria (PKU) subjects using current treatment strategies whose phenylalanine (Phe) concentrations diverge from the UK target guidelines for PKU.

RESEARCH DESIGN AND METHODS

This retrospective, observational, chart review was conducted between 2004 and 2008 at three specialist PKU treatment centres in the UK, and included 125 eligible subjects: 20 adults (18+ years, with ≥4 Phe concentrations measured per year) and 105 children (up to age 17, with ≥6 Phe concentrations measured per year).

RESULTS

The mean percentage of subjects with at least 70% of Phe concentrations within the target range for 0-5-year olds, 6-10 year olds and 11-17 year olds was similar across the period 2004-2008 (57.0%, 56.5% and 57.1%, respectively) and lower (39.4%) in the 18+ year age group. For all ages, across the period the mean was 54.4%. Further analysis of the adult population showed that some subjects were very good at complying with treatment and reporting Phe concentrations. Overall, the percentage of 100% compliance was 15.7% in females and 13.7% in males. The mean duration that subjects were 'out of range' of target Phe concentrations over the study period was approximately 1 year and 3 months and the mean duration for 'significantly out of range' values was approximately 9 months. The most common type of contact made with subjects was by telephone, with a mean number of 16 calls per subject per year.

CONCLUSION

The results support current literature showing that a proportion of subjects with PKU, in particular older subjects, are not fully compliant with their treatment and subsequently have Phe concentrations that depart from national recommendations. However, definitive conclusions may not be drawn due to the retrospective nature of the study and the small number of observed subjects.