The efficacy of dietary therapy for phenylketonuria.

Ninety-four patients with classical phenylketonuria are reviewed. Early treatment with a low phenylalanine diet usually results in normal or near-normal I.Q. Twenty-seven of the 38 patients diagnosed before 2 months of age have an I.Q. in the normal range. Of the other 11, six are dull normal, four are borderline and one is frankly retarded. Adequate reasons are given for the less than optimal results in these 11 early-treated patients. Twenty-one of the 28 patients presenting with abnormal electroencephalograms showed normal tracings soon after initiation of diet and four of the other seven improved. Nine of 12 on continuous anticonvulsant medication at the time of presentation were able to discontinue this soon after institution of dietary measures. Eighteen of the 19 sibling pair comparisons revealed a better ultimate I.Q. in the early-treated sib. A plea for early diagnosis by continuation of newborn screening programs and for centralization of diagnostic confirmation and treatment is made.