Biochemical markers associated with executive function in adolescents with early and continuously treated phenylketonuria.

Debate continues as to why executive function (EF) continues to show impairments in children with early and continuously treated phenylketonuria (ECT-PKU). Using a mixed model, we measured EF in 10 adolescent children with ECT-PKU and 6 sibling controls, and examined associations between EF and (1) phenylalanine (phe) and (2) the phenylalanine : tyrosine ratio (phe : tyr). Measurements were taken on two occasions anticipated to yield variation in concurrent biochemistry resulting from changes in dietary compliance (i.e. holiday vs non-holiday period). A repeated measures anova using the Behaviour Rating Inventory of Executive Function yielded the following results: no significant interactions; two significant group effects of substantially impaired working memory and initiation skills in children with ECT-PKU compared with controls, irrespective of occasion and two significant time effects, suggestive of slightly poorer non-holiday planning and organization scores in both groups. Further analyses revealed that phe levels were not significantly different on these occasions, suggesting that holiday dietary compliance may be better than expected. Correlations between EF and biochemistry in children with PKU showed that participant's lifetime phe : tyr ratio was positively and significantly associated with EF impairment, more so than phe-only measures.