Executive function in adolescents with PKU and their siblings: Associations with biochemistry

The clinical relevance of novel biomarkers as outcome parameter in adults with phenylketonuria

Recent studies in PKU patients identified alternative biomarkers in blood using untargeted metabolomics. To test the added clinical value of these novel biomarkers, targeted metabolomics of 11 PKU biomarkers (phenylalanine, glutamyl-phenylalanine, glutamyl-glutamyl-phenylalanine, N-lactoyl-phenylalanine, N-acetyl-phenylalanine, the dipeptides phenylalanyl-phenylalanine and phenylalanyl-leucine, phenylalanine-hexose conjugate, phenyllactate, phenylpyruvate, and phenylacetate) was performed in stored serum samples of the well-defined PKU patient-COBESO cohort and a healthy control group. Serum samples of 35 PKU adults and 20 healthy age- and sex-matched controls were analyzed using ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry. Group differences were tested using the Mann-Whitney U test. Multiple linear regression analyses were performed with these biomarkers as predictors of (neuro-)cognitive functions working memory, sustained attention, inhibitory control, and mental health. Compared to healthy controls, phenylalanine, glutamyl-phenylalanine, N-lactoyl-phenylalanine, N-acetyl-phenylalanine, phenylalanine-hexose conjugate, phenyllactate, phenylpyruvate, and phenylacetate were significant elevated in PKU adults (p < 0.001). The remaining three were below limit of detection in PKU and controls. Both phenylalanine and N-lactoyl-phenylalanine were associated with DSM-VI Attention deficit/hyperactivity (R2 = 0.195, p = 0.039 and R2 = 0.335, p = 0.002, respectively) of the ASR questionnaire. In addition, N-lactoyl-phenylalanine showed significant associations with ASR DSM-VI avoidant personality (R2 = 0.265, p = 0.010), internalizing (R2 = 0.192, p = 0.046) and externalizing problems (R2 = 0.217, p = 0.029) of the ASR questionnaire and multiple aspects of the MS2D and FI tests, reflecting working memory with R2 between 0.178 (p = 0.048) and 0.204 (p = 0.033). Even though the strength of the models was not considered strong, N-lactoyl-phenylalanine outperformed phenylalanine in its association with working memory and mental health outcomes.

Metabolic control and clinical outcome in adolescents with phenylketonuria

The main neurological, cognitive, and behavioural consequences of phenylketonuria have been eradicated thanks to new-born screening and Phe-restricted diet therapy. However, the effects of high phenylalanine levels during adolescence and adulthood on neurocognitive functions remain a concern. This systematic review aimed at collecting clinical data suggesting the safest metabolic target for early treated PKU during the second decade of life. Twenty studies met the inclusion criteria for full-text review. Relevant studies included papers that (a) examined the relationship between metabolic control and neurocognitive functions during adolescence or (b) investigated the impact of metabolic control in adolescence on adult outcomes. Most studies showed a positive correlation between metabolic control during adolescence and neurocognitive outcomes across ages. This was true both for IQ and executive functions, although data on executive functions were less clear, and it remains to be established whether they are more vulnerable to Phe than IQ. Taken together present evidence confirm brain vulnerability to Phe during adolescence and suggests that low average Phe levels and low Phe fluctuations should be maintained throughout life. While results are fully compatible with current European recommendations, clinical and methodological limitations coupled with remarkable interindividual variability prevented a clear identification of a safe threshold for Phe blood levels during adolescence.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

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

OBJECTIVE

To provide a comprehensive systematic review of the literature by examining studies published on all cognitive aspects of children with early and continuously treated phenylketonuria (ECT-PKU) included in the databases Medline, PsycINFO, and PsycARTICLE.

METHOD

In addition to a classical approach, we summarized methodology and results of each study in order to discuss current theoretical and methodological issues. We also examined recent advances in biochemical markers and treatments of PKU, with implications for future research on metabolic control and its role as a determinant of neuropsychological outcome.

RESULTS

Consistent with previous reviews, the hypothesis of a specific and central executive impairment in children with ECT-PKU was suggested. However, findings are inconclusive regarding the nature of executive impairments as well as their specificity, impact on everyday life, persistence over time, and etiology.

CONCLUSION

Given the current state of the science, we suggest future directions for research that utilizes a developmental and integrative approach to examine the effects of recent advances in biochemical markers and treatment of PKU. (JINS, 2019, 25, 624-643).

The influence of blood phenylalanine levels on neurocognitive function in adult PKU patients

It is well known that hyperphenylalaninemia caused by phenylketonuria (PKU) negatively influences cognitive performance. Several tests have been used to study these functions. Until now, no universal, optimal tool has been developed for detecting PKU-caused brain dysfunctions. Using computerized neuropsychological tests during daily routine would be helpful for screening subclinical brain deficits in adult PKU patients. In a monocentric, cross-sectional study, adult patients with PKU (n = 46; median age = 29.5 years; female/male ratio = 21/25) were tested with the computerized Cambridge Cognition (CANTAB) test measuring neurocognitive functions. Patients were divided into two groups: The "on diet" group included patients whose blood Phe-level was under 600 μmol/l (n = 20), and the "loose diet" group included patients whose blood Phe-level was above 600 μmol/l (n = 26) at the examination time. The results of the PKU-affected individuals were compared with a healthy control group (n = 31; median age = 25 years; female/male ratio = 11/20). Compared with the control group, PKU patients had significantly worse test results in memory, problem-solving skills, and strategy. However, there were no significant differences in response speed or initial thinking time. There was no correlation between the blood Phe-level, tyrosine (Tyr)-level or Phe/Tyr ratio and the different cognitive test results. There were no significant differences in test results between the two PKU subgroups. Several cognitive functions measured by CANTAB are negatively influenced by hyperphenylalaninemia in adult PKU patients. However, response speed and initial thinking time were not impaired as seriously as other functions. Patients with lower Phe-levels failed to achieve better test results than patients whose Phe-levels were notably elevated.

Multicompartment analysis of protein-restricted phenylketonuric mice reveals amino acid imbalances in brain

BACKGROUND

The mainstay of therapy for phenylketonuria (PKU) remains dietary protein restriction. Developmental and neurocognitive outcomes for patients, however, remain suboptimal. We tested the hypothesis that mice with PKU receiving protein-restricted diets would reveal disruptions of brain amino acids that shed light on these neurocognitive deficits.

METHOD

Phenylalanine hydroxylase-deficient (PKU) mice and parallel controls (both wild-type and heterozygous) were fed custom diets containing 18, 6, and 4 % protein for 3 weeks, after which tissues (brain, liver, sera) were collected for amino acid analysis profiling.

RESULTS

Phenylalanine (phe) was increased in all tissues (p < 0.0001) of PKU mice and improved with protein restriction. In sera, decreased tyrosine (p < 0.01) was corrected (defined as not significantly different from the level in control mice receiving 18 % chow) with protein restriction, whereas protein restriction significantly increased many other amino acids. A similar trend for increased amino acid levels with protein restriction was also observed in liver. In brain, the effects of protein restriction on large neutral amino acids (LNAAs) were variable, with some deficit correction (threonine, methionine, glutamine) and no correction of tyrosine under any dietary paradigm. Protein restriction (4 % diet) in PKU mice significantly decreased lysine, arginine, taurine, glutamate, asparagine, and serine which had been comparable to control mice under 18 % protein intake.

CONCLUSION

Depletion of taurine, glutamate, and serine in the brain of PKU mice with dietary protein restriction may provide new insight into neurocognitive deficits of PKU.

[Factors influencing the quality of life of 104 children with phenylketonuria in Anhui Province, China]

OBJECTIVE

To investigate the factors influencing the quality of life (QOL) of children with phenylketonuria (PKU) in Anhui Province, China.

METHODS

A total of 104 PKU children who were diagnosed and treated in three major maternal and child health hospitals in Anhui Province were enrolled as study subjects. The PedsQL™ 4.0 Generic Core Scales were used to evaluate the quality of life of these children. The multivariate logistic regression analysis was used to evaluate the factors influencing the QOL.

RESULTS

The 104 PKU children had significantly lower overall QOL score and scores on the subscales of physiological functioning, emotional functioning, and social functioning than the general school-age children (P<0.01). They also had a significantly lower score on the physiological domain consisting of emotional functioning, social functioning, and role functioning than the general school-age children (P<0.01). The multivariate logistic regression analysis showed that an older age (≥4 years) of PKU children was the risk factor for poor QOL (OR=8.569, P<0.01), and guardians' engagement at enterprises or institutions was the protective factor for QOL (OR=0.206, P<0.05).

CONCLUSIONS

PKU children have a low level of QOL, and age and guardians' occupation are factors influencing the QOL.

[Factors influencing the quality of life of 104 children with phenylketonuria in Anhui Province, China]

OBJECTIVE

To investigate the factors influencing the quality of life (QOL) of children with phenylketonuria (PKU) in Anhui Province, China.

METHODS

A total of 104 PKU children who were diagnosed and treated in three major maternal and child health hospitals in Anhui Province were enrolled as study subjects. The PedsQL™ 4.0 Generic Core Scales were used to evaluate the quality of life of these children. The multivariate logistic regression analysis was used to evaluate the factors influencing the QOL.

RESULTS

The 104 PKU children had significantly lower overall QOL score and scores on the subscales of physiological functioning, emotional functioning, and social functioning than the general school-age children (P<0.01). They also had a significantly lower score on the physiological domain consisting of emotional functioning, social functioning, and role functioning than the general school-age children (P<0.01). The multivariate logistic regression analysis showed that an older age (≥4 years) of PKU children was the risk factor for poor QOL (OR=8.569, P<0.01), and guardians' engagement at enterprises or institutions was the protective factor for QOL (OR=0.206, P<0.05).

CONCLUSIONS

PKU children have a low level of QOL, and age and guardians' occupation are factors influencing the QOL.