Visual event-related potentials in children with phenylketonuria RM Henderson 1 , DL McCulloch 1 , AM Herbert 1,2 , PH Robinson 3 and MJ Taylor 4 Department of Vision Sciences, Glasgow Caledonian University 1 , Glasgow, Scotland; Department of Psychology, University of North Texas 2 , Denton, TX, USA; Royal Hospital for Sick Children 3 , Yorkhill, Glasgow, Scotland; CERCO 4 , Faculte ´ de Me ´decine de Rangueil, Toulouse, France Henderson RM, McCulloch DL, Herbert AM, Robinson PH, Taylor MJ. Visual event-related potentials in children with phenylketonuria. Acta Pædiatr 2000; 89: 52–7. Stockholm. ISSN 0803– 5253 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 mmol/l. The most recent Phe levels were 56–624 mmol/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. & Event-related potentials, phenylalanine, phenylketonuria, reaction time, P3, visual evoked potentials RM Henderson, Department of Vision Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 0BA, Scotland (Tel. 44 (0) 141 331 3382, fax. 44 (0) 141 331 3387, e-mail. rmhe@gcal.ac.uk) Phenylketonuria (PKU) is an inherited metabolic dis- order that prevents the conversion of the amino acid phenylalanine (Phe) to tyrosine. Without treatment from infancy, normal development is severely disrupted (for review, see (1)). Treatment for PKU consists of restriction of dietary Phe and intake of amino acid supplements that contain extra tyrosine. In the past, dietary control was discontinued between 8–14 y of age, because clinical changes are less noticeable after this age with increased Phe (2). In addition, the unpalatable nature of the diet does not encourage compliance. Currently, there is a growing body of evidence that neurophysiological and neuropsychological changes are associated with high Phe levels in later childhood and even adulthood. High Phe levels affect the intellectual quotient (IQ) up to the age of 10 y (3). There are also changes in reaction time and executive function in childhood and adulthood in early-treated PKU (for review, see (4)). The hypothesis has been advanced that deficits in executive function (defined as anticipation, planning, self-monitoring and flexibility) are due to deficient dopamine levels in the prefrontal cortex (5). Recent advances in brain imaging have also shown abnormalities in patients with PKU. Magnetic reso- nance imaging (MRI) has shown abnormalities in the white matter of the brain in asymptomatic, early-treated children and adults (6, 7). These MRI abnormalities were related to recent levels of Phe and length of time since dietary treatment ceased, and were independent of Phe levels early in life (6). Event-related potentials (ERPs) are electrical poten- tials recorded from the surface of the scalp. Early peaks are sensitive to sensory processing, whilst later peaks are involved with cognitive processing. For instance, the third positive peak (P3) is a late cognitive potential that has a larger amplitude if a stimulus is infrequent and task-relevant (for review, see (8)). ERPs have excellent temporal resolution; changes have been found in the early peaks of scalp-recorded potentials of children and adults with PKU (9–16). PKU may also affect cognitive P3, as recent studies have shown that dopamine monotherapy in Parkinson’s disease causes a reduction in P3 latency (17) for an auditory task. This has led to suggestions that the P3 has a dopaminergic component. The aim of this study was to measure electrophysio- logical and behavioural correlates of visual processing in a group of children with early-treated PKU. We wished to determine if the usual age-related changes in latency and amplitude of the ERPs (for review, see (18))  Scandinavian University Press 2000. ISSN 0803-5253 Acta Pñdiatr 89: 52±7. 2000