[Phenylketonuria: early diagnosis and mental development (author's transl)]

The relationship of early diagnosis and treatment to mental development was studied in 152 children with phenylketonuria. The average IQ at onset of the diet, if within the first two months of life, was 105 in 60 children, 70 in 28 patients if between 3 and 12 months of life, and 53 in 31 of between the thirteenth month and the end of the second year. In 33 children in whom the diagnosis had been made after the second year, diet being started this late, average IQ was 50 with correspondingly greater scatter in the severe mental deficiency range.