Prefrontal Dysfunction in Early and Continuously Treated Phenylketonuria

Abstract

In this study, we tested the hypothesis that patients with early and continuously treated phenylketonuria (PKU) are selectively impaired in cognitive functions dependent on the prefrontal cortex (PFC) over a wide age range. Thirty-six patients with PKU between 8 and 20 years of age and 36 controls matched for age, sex, and educational level of both parents performed computerized versions of tests shown to be sensitive to PFC functions. To assess specificity, we selected within each test measures shown to be specifically impaired by PFC damage as well as measures not specifically impaired by damage to the PFC (control measures). A contrast sensitivity test was administered to obtain additional and independent evidence for the mechanism proposed to underlie the specific PFC deficits. Patients with early and continuously treated PKU demonstrated impairments on 3 of the 4 PFC measures but not on any of the control measures. Furthermore, they were found to be significantly less sensitive to contrast than were the matched controls. Together, these results seem to confirm that specific deficits in PFC functions persist in older patients with early and continuously treated PKU. The results with respect to the biochemical mechanism underlying these deficits were less clear. They do suggest, however, that some of the deficits may be ameliorated by stricter dietary treatment.