Background: Patients with early-treated PKU show white matter abnormalities in MRIs, but no correlation with other clinical aspects (e.g. IQ, VEP) was confirmed.

Study design: Cross-sectional, control group for neuropsychological tasks.

Subjects: 29 early-treated adult patients with classical PKU(mean age 20.7 [18-25]), 24 control subjects (similar in age, sex, and educational status of the family).

Methods: MRI 1.0 T (T1-, T2- and proton density weighted images), IQ-test (WAIS-R), VEP, neuropsychological tasks (SVAT), plasma phenylalanine level.

Results: MRI revealed a high frequency of supra- and infratentorial abnormalities. Visuo-motor reaction time was higher in PKU(Z=-1.8, p<0.05), and sustained attention ability was reduced (Z=-3.7, p<0.001). MRI grade (derived from T2- weighted images) was correlated with reaction time (r=.53, p<0.01) and sustained attention (r=41, p<0.05), but not with IQ or VEP results.

Conclusions: Neuropsychological test results reveal for the first time that MRI white matter changes may be associated with impaired information processing in patients with PKU.