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Neuropsychology of early-treated phenylketonuria: specific executive function deficits
M C Welsh1, B F Pennington, S Ozonoff
1Department of Psychology, University of Denver, CO 80208.
Insights
Children with early-treated phenylketonuria (PKU) show specific executive function impairments, linked to phenylalanine levels. These deficits in executive functions like planning suggest subtle prefrontal dysfunction even with dietary management.
Area of Science:
- Neuroscience
- Developmental Psychology
- Metabolic Disorders
Background:
- Phenylketonuria (PKU) is a metabolic disorder requiring early dietary intervention.
- Elevated phenylalanine (Phe) may impact neurotransmitter levels, potentially affecting brain function.
- Executive functions (EF) are crucial for cognitive control and goal-directed behavior.
Purpose of the Study:
- To investigate if early-treated PKU children exhibit selective executive function deficits.
- To explore the relationship between phenylalanine levels and executive function performance.
- To examine the proposed biochemical mechanism involving dopamine depletion and prefrontal dysfunction.
Main Methods:
- Compared executive function performance in 11 preschool children with early-treated PKU against 11 age- and IQ-matched controls.
- Administered a battery of executive function tasks and a recognition memory task.
- Correlated executive function scores with phenylalanine levels within the PKU group.
Main Results:
- PKU children demonstrated significantly impaired executive function composite scores compared to controls.
- No significant differences were found in recognition memory between the groups.
- Executive function composite scores negatively correlated with phenylalanine levels in PKU children, independent of IQ.
Conclusions:
- Early-treated PKU is associated with specific deficits in executive functions.
- Phenylalanine levels may directly impact executive function performance in PKU.
- Findings support a biochemical mechanism involving dopamine and prefrontal dysfunction in PKU-related cognitive impairments.
Abstract:
This study explored the hypothesis that children with early-treated phenylketonuria (PKU) are selectively impaired on executive function measures, even when still on diet. The rationale for this hypothesis is that even mild elevations in phenylalanine (Phe) can lead to lower central levels of biogenic amines, including dopamine (DA). We hypothesize that this mild DA depletion causes subtle prefrontal dysfunction, which in turn affects executive functions such as set maintenance, planning, and organized search. 11 preschool early-treated PKU children (M age = 4.64) and a sample of age- and IQ-matched unaffected peers (n = 11) were evaluated on a battery of executive function (EF) measures. In addition, a "non-executive function" task, recognition memory, was administered to all subjects. Group comparisons demonstrated that PKU children were significantly impaired on an executive function composite score; there were no group differences, however, in recognition memory. These results supported the hypothesized specific deficit in executive function. Furthermore, within the PKU group the executive function composite score was significantly negatively correlated with concurrent phenylalanine levels, even after controlling for the correlation between IQ and executive function skills. This second finding provides support for the proposed biochemical mechanism underlying the specific cognitive deficits.