Event-related potential correlates of selective processing in early- and continuously-treated children with phenylketonuria: effects of concurrent phenylalanine level and dietary control

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.

Behavioral and Emotional Problems in Early-Treated Brazilian Children and Adolescents with Phenylketonuria

Background

Phenylketonuria (PKU) is an inborn error of metabolism caused by mutations in the phenylalanine hydroxylase (PAH) gene. When untreated, PKU leads to a significant intellectual deficiency. Although early initiation of dietary therapy allows normal cognitive development, low adherence to treatment may result in neuropsychological deficits, including attention problems. This study was performed to evaluate emotional and behavioral problems in early-treated children and adolescents with PKU using the Child Behavior Checklist – CBCL/6–18 answered by parents.

Material/Methods

The study included 36 PKU patients. The mean scores of internalizing, externalizing, and total problems, syndrome scales, and DSM-IV-oriented scales of patients were compared with those of controls. An analysis to evaluate the importance of adherence to treatment and presence of intellectual disability was also performed.

Results

There were no significant differences between patients and controls for almost all CBCL/6–18 scales, with the exception of the Attention Problem Scale – CBCL-APS. The mean (±SD) of the CBCL-APS scores of patients (7.86±5.33) was considerably higher than the mean of the controls (6.07±4.37; p=0.016), but not different from the mean of a matched control subsample (6.69±4.46; p=0.316). The difference between the mean of the scores of DSM-IV/ADHD scale of patients (6.72±4.07) and controls (5.73±3.56; p=0.102) was not significant. Non-adherence to treatment and intellectual disability had a negative impact on both CBCL-APS and DSM-IV/ADHD scale scores.

Conclusions

Our findings indicate a significant prevalence of parents’ complaints of attention problems and hyperactivity in non-adherent to treatment and intellectually low performing patients with PKU.

Outcomes of referrals to Child Protective Services for medical neglect in patients with phenylketonuria: Experiences at a single treatment center

Phenylketonuria (PKU) results in an accumulation of phenylalanine (phe) in the blood which can lead to multiple health consequences in affected individuals. Treatment for PKU is available; however adherence to medical management recommendations can be difficult. When recommendations are not followed and the health of a child is at risk, one intervention that may be necessary is a referral for medical neglect to the local child protective services (CPS) agency. This study summarizes the cases that were referred from our metabolic clinic at the Children's Hospital of Michigan to CPS, and the outcomes of that intervention. CPS referrals helped to improve adherence to medical management recommendations in the majority of cases, including a lower blood phe level for the child; however, at times that improvement did not occur until after a second referral and/or the child's temporary removal from the home.

Evaluation of effectiveness and outcome of PKU screening and management in the State of Sergipe, Brazil

OBJECTIVES

Phenylketonuria (PKU) was the first inherited metabolic disease known to cause mental retardation for which a newborn screening program (NBS) was developed. The objective of this study was to evaluate the effectiveness of PKU NBS and the management of cases in the northeastern Brazilian state of Sergipe (SE).

MATERIALS AND METHODS

We reviewed the phenylalanine concentrations in filter-paper collected from the heel (PKUneo) of 43,449 newborns; blood concentrations obtained by venipuncture in the subjects with abnormal PKUneo; the children's age at several phases of the program, the incidence of the disease from January 2007 to June 2008; and metabolic control of the patients.

RESULTS

The coverage of NBS/SE was 78.93%. The children's age was 10 ± 7 days at PKUneo collection. Twelve children were recalled based on the PKUneo cutoff value at 28 ± 13 days. From these, the concentrations of phenylalanine collected by venipuncture were normal in five children. The incidence of hyperphenylalaninemia was 1/43,449, and of PKU was 1/8,690 (5 cases). One suspected subject died. Another death occurred in the cohort, in a confirmed PKU case. PKU treatment began within 51 ± 12 days of life. In the four patients under dietary phenylalanine restriction, metabolic control was often difficult.

CONCLUSIONS

PKU NBS/SE has satisfactory coverage and adequate cutoff for recalling patients and diagnosis, but the onset of treatment is delayed, and follow-up metabolic control is frequently inadequate.

Age-related psychophysiological vulnerability to phenylalanine in phenylketonuria

BACKGROUND

Phenylketonuria (PKU) is caused by the inherited defect of the phenylalanine hydroxylase enzyme, which converts phenylalanine (Phe) into tyrosine (Tyr). Neonatal screening programs and early treatment have radically changed the natural history of PKU. Nevertheless, an increased risk of neurocognitive and psychiatric problems in adulthood remains a challenging aspect of the disease. In order to assess the vulnerability of complex skills to Phe, we explored: (a) the effect of a rapid increase in blood Phe levels on event-related potentials (ERP) in PKU subjects during their second decade of life; (b) the association (if existing) between psychophysiological and neurocognitive features.

METHODS

Seventeen early-treated PKU subjects, aged 10-20, underwent ERP [mismatch negativity, auditory P300, contingent negative variation (CNV), and Intensity Dependence of Auditory Evoked Potentials] recording before and 2 h after an oral loading of Phe. Neurocognitive functioning, historical and concurrent biochemical values of blood Phe, Tyr, and Phe/Tyr ratio, were all included in the statistical analysis.

RESULTS

Event-related potential components were normally detected in all the subjects. In subjects younger than 13 CNV amplitude, W2-CNV area, P3b latency, and reaction times in motor responses were negatively influenced by Phe-loading. Independently from the psychophysiological vulnerability, some neurocognitive skills were more impaired in younger patients. No correlation was found between biochemical alterations and neurocognitive and psychophysiological findings.

CONCLUSION

The vulnerability of the emerging neurocognitive functions to Phe suggests a strict metabolic control in adolescents affected by PKU and a neurodevelopmental approach in the study of neurocognitive outcome in PKU.

A comparison of phenylketonuria with attention deficit hyperactivity disorder: do markedly different aetiologies deliver common phenotypes?

Phenylketonuria (PKU) is a well-defined metabolic disorder arising from a mutation that disrupts phenylalanine metabolism and so produces a variety of neural changes indirectly. Severe cognitive impairment can be prevented by dietary treatment; however, residual symptoms may be reported. These residual symptoms appear to overlap a more prevalent childhood disorder: Attention Deficit/Hyperactivity Disorder (ADHD). However, the aetiology of ADHD is a vast contrast to PKU: it seems to arise from a complex combination of genes; and it has a substantial environmental component. We ask whether these two disorders result from two vastly different genotypes that converge on a specific core phenotype that includes similar dysfunctions of Gray's (Gray, 1982) Behavioural Inhibition System (BIS), coupled with other disorder-specific dysfunctions. If so, we believe comparison of the commonalities will allow greater understanding of the neuropsychology of both disorders. We review in detail the aetiology, treatment, neural pathology, cognitive deficits and electrophysiological abnormalities of PKU; and compare this with selected directly matching aspects of ADHD. The biochemical and neural pathologies of PKU and ADHD are quite distinct in their causes and detail; but they result in the disorder in the brain of large amino acid levels, dopamine and white matter that are very similar and could explain the overlap of symptoms within and between the PKU and ADHD spectra. The common deficits affect visual function, motor function, attention, working memory, planning, and inhibition. For each of PKU and ADHD separately, a subset of deficits has been attributed to a primary dysfunction of behavioural inhibition. In the case of ADHD (excluding the inattentive subtype) this has been proposed to involve a specific failure of the BIS; and we suggest that this is also true of PKU. This accounts for a substantial proportion of the parallels in the superficial symptoms of both disorders and we see this as linked to prefrontal, rather than more general, dysfunction of the BIS.

Mental health and social functioning in early treated Phenylketonuria: the PKU-COBESO study

This article presents a new Dutch multicenter study ("PKU-COBESO") into cognitive and behavioral sequelae of early and continuously treated Phenylketonuria (PKU) patients. Part of the study sample will consist of young adult PKU patients who have participated in a large neuropsychological study approximately 10 years ago, when they were 7-to-15-year-olds (Huijbregts et al., 2002 [1]). Their neurocognitive development will be mapped in association with their earlier and continued metabolic history, taking into account possible changes in, for instance, medication. A second part of the sample will consist of PKU patients between the ages of 7 and approximately 40 years (i.e., born in or after 1974, when neonatal screening was introduced in The Netherlands), who have not participated in the earlier neuropsychological study. Again, their cognitive functioning will be related to their metabolic history. With respect to aspects of cognition, there will be an emphasis on executive functioning. The concept of executive functioning will however be extended with further emphasis on the impact of cognitive deficits on the daily lives of PKU patients, aspects of social cognition, social functioning, and behavior/mental health (i.e., COgnition, BEhavior, SOcial functioning: COBESO). In addition to a description of the PKU-COBESO study, some preliminary results with respect to mental health and social functioning will be presented in this article. Thirty adult PKU patients (mean age 27.8, SD 6.4) and 23 PKU patients under the age of 18 years (mean age 11.0, SD 3.3) were compared to 14 (mean age 26.9 years, SD 5.9) and 7 matched controls (mean age 10.5, SD 2.6) respectively, with respect to their scores on the Adult Self-Report or Child Behavior Checklist (measuring mental health problems) and the Social Skills Checklist or Social Skills Rating System (measuring social skills). Whereas there were very few significant group differences (except for mental health problems in the internalizing spectrum for adult PKU patients), possibly due to the small control groups, several significant associations between mental health problems and Phe levels were observed for the PKU patients. Childhood Phe levels and internalizing problems for adult PKU patients were related; concurrent Phe was associated with both internalizing and externalizing behavioral problems for those under the age of 18. These preliminary results underline the importance of early dietary adherence.

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.

Routine use of CANTAB system for detection of neuropsychological deficits in patients with PKU

Several studies have reported neuropsychological deficits related to hyper phenylalaninemia in patients with phenylketonuria (PKU). As computerized neuropsychological tests seem to be promising in the detection of such abnormalities, we aimed to assess the usefulness of routine use of CANTAB system in PKU clinic. A group of 49 PKU patients aged >16 years were tested by means of computerized CANTAB tests measuring speed of response, response inhibition, sustained attention, and working memory capacity. The scores achieved by study participants were analyzed with respect to their blood phenylalanine concentrations. Proper dietary control was observed in 22 patients, whereas in the remaining 27 persons, blood phenylalanine concentrations exceeded the recommended range. The results of the tests assessing sustained attention, working memory, and inhibitory control achieved by the non-compliant patients were significantly worse in comparison with patients maintaining proper diet. However, the mean scores achieved by treatment-adherent patients were also worse than expected, what could probably be related to problems with early start of treatment during their infancy. Our results confirmed the presence of specific neuropsychological deficits related to hyperphenylalaninemia in adults and adolescents with PKU. In our opinion, routine use of computerized neuropsychological tests should be recommended in PKU clinics.

Cognitive, neurophysiological, neurological and psychosocial outcomes in early-treated PKU-patients: a start toward standardized outcome measurement across development

The aim of this paper is to provide a concise summary of findings from outcome studies in early-treated phenylketonuria (PKU). The paper should not be considered as an extensive review of the many different outcome measures that have been used in PKU-research, but as an attempt to integrate such findings so that they will be of additional value for day to day monitoring of PKU-patients and may direct future research to fill the present gaps of knowledge. Neurological, neuropsychological, neurophysiological, neuroimaging, quality of life, and psychosocial findings will be discussed in the context of their potential contributions to lifelong follow-up and treatment of PKU-patients being summarized in statements.