A neurological evaluation of adult phenylketonuria in Northern Ireland.

To investigate the extent of neurological disease in adults with phenylketonuria and also their requirement for specialist medical services, we assessed 27 such patients in Northern Ireland. Most had been diagnosed early and with one exception had dietary relaxation by early adolescence. Abnormal neurological features were elicited in 21/27 cases with significant delay of visual evoked potentials and somatosensory evoked potentials occurring in 63.6 and 13.6% of cases respectively. Periventricular white matter abnormalities were observed in 5/12 patients undergoing magnetic resonance imaging, whilst phenylalanine levels were high (mean 1,226 micromol/l). These data accord with the observation that even early treated patients with phenylketonuria can have significant neurological morbidity in adulthood, although the correlation with current or recent dietary control is unclear and requires further study.