Phenylketonuria: Implications of Initial Serum Phenylalanine Levels on Cognitive Development

Abstract

This study investigated influences of diagnostic phenylalanines, age at initiation of diet, and dietary control, separately and in combination, on cognitive development for 29 phenylketonuric children (17 boys and 12 girls) who ranged in age from 1 to 1,184 days. Initial serum phenylalanine concentrations and age at initiation of therapy were significantly related to cognitive development, whereas neither dietary and biochemical control relative to blood levels of phenylalanine or for these variables in combination exerted a statistically significant effect on measures of functioning. The interaction between initial serum phenylalanine level and age at onset of diet did reach nearly significant proportions, suggesting that the relation between diagnostic phenylalanines and subsequent cognitive development in the phenylketonuric population warrants further study. Despite an approximately 13-point decrease in IQs between initial (1 yr.) and most recent measurements (3 yr.), all 29 children were functioning in the normal or near-normal intellectual range at the most recent testing.