Cranial MRI in PKU: evaluation of a critical threshold for blood phenylalanine.

A group of 15 adolescent patients with PKU and good life time blood phenylalanine control was tested for white matter abnormalities on MRI. Five of the patients presented mild to moderate abnormalities in association with blood phenylalanine levels above 5.0 mg/dl. Patients with and without MRI changes could statistically not be discriminated by blood phenylalanine concentrations at the time of investigation as well as by phenylalanine levels of different time periods prior to MRI examination.