Cognitive Findings and Behavior in Children and Adolescents with Phenylketonuria

Objective: The primary aim of this study was to assess cognitive development, in particular that of executive functions (EFs), and behavioral findings for patients with early treated phenylketonuria (PKU). Furthermore, we evaluated the relationships of our findings with plasma levels of Phe and adherence to dietary prescriptions. Methods: A cross-sectional design was adopted. Patients who had early treated PKU, who were older than 4 years, and who were regularly seen by a physician were enrolled in the study. Cognitive development was assessed with Wechsler Scales appropriate to the chronological age of subjects in the study. Executive functions were assessed using the Tower of London test, and behavioral findings were quantified with the Child Behavior Checklist. Results: Thirty-five patients were enrolled (mean age 11.5 years, SD +/- 6.2). The mean Full Scale intelligence quotient was in the normal range (93.4 +/- 17.4), without significant difference between the verbal intelligence quotient (mean, 94.3 +/- 16.1) and performance intelligence quotient (mean, 93.9 +/- 18.0). The majority of patients showed a deficit within the EF domain of cognitive abilities (mean lower than 1.8 SD of the normal mean), 8 of them showing a score <2 SD lower than the normal mean. Internalizing problems were also observed in 12 patients (38.7%) and were higher in adherent patients and in patients with a lower intelligence quotient. Conclusion: After early diagnosis and treatment of PKU, residual problems can be found in EFs of patients not achieving satisfactory Phe levels, while scores of internalizing behaviors were higher in compliant patients.