Executive functioning in children and adolescents with phenylketonuria.

This study addresses the effects of dietary adherence, phenylalanine (phe) levels, and age on performance of executive functioning (EF) tasks in children and adolescents with phenylketonuria (PKU). We herein collate formerly discrete findings to understand the relationship among actual clinical parameters and EF in PKU. Fifteen subjects (age range 8-20 years) with PKU were compared with the normative sample on the Delis-Kaplan EF Battery and on the Wechsler Abbreviated Scales of Intelligence to examine the relationship between EF skills, phe levels, age, and dietary adherence. At the time of the assessment, the mean age of participants was 14.8 years, mean lifetime phe levels ranged from 216 to 1200 microM (mean 594 microM); and concurrent phe levels ranged from 222 to 1730 microM (mean 660 microM). Children and adolescents with PKU showed lower performance in several EF skills: initiation of problem solving, concept formation, and reasoning. Performance on EF tasks requiring inhibitory control, cognitive flexibility and set shifting decreased at higher phe levels. Phe levels were positively correlated to age and inversely related to dietary adherence. We conclude that dynamic clinical parameters appear to govern EF in patients with PKU. We suggest that when adolescents decrease dietary compliance, changes in EF skills occur. Therefore, there is a need to specifically monitor EF skills in patients with PKU during the transition to, and during, adolescence.