Visual event-related potentials in children with phenylketonuria.

Visual event-related potentials (ERPs) were examined in 16 children (aged 5-14 y) with phenylketonuria (PKU) and 16 age- and sex-matched controls. Lifetime median measures of phenylalanine (Phe) were 230-460 micromol/l. The most recent Phe levels were 56-624 micromol/l. ERPs were recorded whilst the children performed a discrimination task. All stimuli were square wave gratings degree, which appeared for 33 ms. A response to an infrequent grating that differed in orientation or spatial frequency was required. The older children with PKU had a delay in the first peak (P1) of the ERP, and age-related changes in the amplitude of P1. There was attenuation of the second peak across age groups in PKU. There was no evidence of reduced response accuracy or longer reaction times in children with PKU. Latencies of the cognitive P3 were not delayed in PKU. The delayed early peaks are consistent with previous studies that have shown delayed visual evoked potentials in PKU. The lack of differences in reaction time and P3 may be due to relatively good Phe control in children with PKU, or to the simplicity of the task. Suggestions are made for future ERP studies of PKU.