“…In phenylketonuria there is a lack of pigment in the skin, hair, and substantia nigra (Crome, 1962) owing to the underlying deficiency of phenylalanine hydroxylase (Hassel and Brunsting, 1959). The same defect could also result in a decrease in brain dopamine (a precursor of melanin) and the excess phenylpyruvic acid found in phenylketonuria might further deplete dopamine by condensation (Robbins, 1968).…”