Termination of strict diet therapy in phenylketonuria. A study on EEG sleep patterns and computer spectral analysis

For several years and under various aspects we have studied diet termination in twenty-two early and late treated patients with phenylketonuria. Time of diet termination was the completed eighth year. For evaluation of possible functional CNS deficits, we applied psychometric tests, methods for testing psychomotor behavior and, in addition, neurophysiological parameters and registrations of sleep EEG. EEG morphology was studied visually and the rhythms of the different phases of sleep were quantified by computerized spectral analysis. EEG was studied during diet therapy when phenylalanine levels in blood were low and after a relatively short period of four months with elevated phenylalanine blood levels. At least two years after diet termination with correspondingly elevated phenylalanine blood levels the EEG was studied once more. Compared to the respective findings before diet termination in these patients there were no significant changes of the sleep EEG seen, neither on visual nor on spectral analysis. We have seen in this study minor EEG changes in early treated children and overtly pathological EEG changes in late treated PKU patients with cerebral damage, both before and after diet termination. Ultrastructural CNS defects may be the cause of these anomalies which do not respond to the actual biochemical situation at the age of eight to ten years. The morphology of such defects may include altered synaptic maturation and may occur already in an early phase before the diet therapy is implemented.