White matter pathology in phenylketonuria.

Early-treated phenylketonuria (PKU) is associated with a range of neuropsychological impairments. Proposed mechanisms for these impairments include dopamine depletion and white matter pathology. Neuroimaging studies demonstrate high-signal intensity in the periventricular white matter in most PKU patients, which can extend into subcortical and frontal regions in more severe cases. A review of histopathology and neuroimaging studies reveals that diffuse white matter pathology in untreated PKU patients is likely to reflect hypomyelination (lack of myelin formation), while in early-treated patients white matter abnormalities observed on magnetic resonance imaging (MRI) is likely to reflect intramyelinic edema. Research demonstrates that this pathology is associated with metabolic control and may be reversed with adherence to a strict low-phenylalanine (Phe) diet. While the functional significance of white matter pathology in PKU is not certain, there is some evidence that these abnormalities are associated with functional impairments when the pathology extends into subcortical and frontal regions.