Treatment of classical phenylketonuria.

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Abstract
The results of dietary treatment of this group of confirmed phenylketo-nurics is presented. The small number treated from the first 3 months of life maintained normal intelligence, provided serum phenylalanine control was good. The intelligence quotient (IQ) was lower in those whose serum phenylalanine exceeded 12 mg/100 ml after infancy, and also in 1 child whose serum phenylalanine was less than 2 mg/100 ml during most of his first year. Forty per cent of children treated after the age of 6 months had a recent IQ of more than 60(Tested at age 2 years or more), contrasted with 12% of comparable untreated cases. Decline of IQ after stopping the diet at the age of 2 years, and return towards normal after the diet was reinstituted at 3 years, were demonstrated in 1 child. The results of stopping the diet in older children were variable, but caution is advocated. The problems of diagnosis, and the meticulous treatment necessary to avoid both phenylalanine excess and deficiency, are such that cases detected by infant screening surveys should be referred to special centers wherever possible.