PHENYLALANINE PRODUCES CHANGES IN PLASMA L-DOPA, EEG MEAN POWER FREQUENCY AND PERFORMANCE IN TREATED PHENYLKETONURIC PATIENTS

Abstract

We previously reported in 10 patients with phenylketonuria (PKU) that performance and biogenic amine excretion fell when blood phenylalanine (phe) was elevated (Ped. Res. 17:213A, 1983). Here we extend this study to include four additional children with PKU age 7-10 years and evaluate electrical changes by EEG using mean power frequencies (MPF) determined by Fourier transformation. We altered the diet during three, nine-day periods using a triple-blind, double cross-over research protocol. All patients achieved a plasma phe concentration of greater than 1.2 μM during the loading phase. Plasma L-DOPA was measured and EEGs were performed on the 7,8, and 9th days of each study period. On the 9th day of each period, tests of neuropsychological performance, attention and vigilance were administered. During phe loading the plasma L-DOPA fell, tests of performance deteriorated and attention was not sustained. When blood phe was elevated the MPF of EEGs decreased reflecting a shift to slow wave forms. During periods of phe restricted diet these parameters reverted to baseline. We conclude that the EEG-MPF and certain tests of performance are impaired by high plasma phe concentration, that these effects are mediated through decreased L-DOPA, and that they are transient.