[A case report of mild from of phenylketonuria].

We report a 19-year-old man with mild form of phenylketonuria. The diagnosis was first made when he was examined for the tremor at 19 years of age. He had not received the Guthrie's screening test for phenylketonuria in infancy. His development of speech and walking was almost normal. Action and positional tremor developed at two years of age, and psychomotor deterioration at five years. His intelligence was of borderline, and he entered the special class for the mentally retarded at elementary school and junior high school. His skin and iris were less pigmented than those of Japanese young adults, and his hair was rather reddish. He had mild action tremor. He showed mild mental retardation, and the WAIS was 46 in PIQ, 70 in VIQ and 53 in total IQ. T2-weighted MRI of the brain showed high signal of the deep white matter around the posterior conus of the lateral ventricles. EEG showed paroxysmal abnormalities. Serum aminogram disclosed a marked elevation of phenylalanine. Analyses of pteridine in the serum and urine disclosed a low ratio of neopterine/biopterine. An assay of the dehydropteridine reductase in erythrocytes was normal. These laboratory data indicated that his condition was caused by a deficiency of phenylalanine hydroxylase deficiency.