Neuropsychological functioning in treated phenylketonuria.

Comprehensive neuropsychological assessment was performed on a series of patients with treated classical phenylketonuria. All patients showed a similar cluster of performance deficits in motor and visual-motor functions, spatial operations, academic skill areas, and select areas of higher level reasoning. The results are consistent with other neuropsychological studies of patients with early and late diet termination that have used differing assessment methods, thus allowing for greater confidence in the findings. Examination of underlying factors indicates that poor motor coordination, limits in the complexity of spatial problem solving, and limits in the amount of information that can be "processed" simultaneously may account for most or all of the performance deficits observed among these patients. Suggestions for future research and both clinical and theoretical implications of the findings are discussed.