[Intellectual development after relaxing the diet at the age of 5 years in typical phenylketonuria].

BACKGROUND

No satisfactory controlled trial has yet been completed on typical phenylketonuria (PKU) patients whose treatment was relaxed at the age of 5 years.

METHODS

27 children having typical PKU were treated before the age of 3 months. The intake of phenylalanine and protein was carefully regulated during the first 5 years of life, after which the treatment was relaxed. All children were evaluated after at least 6 years on the relaxed diet. Their IQ scores and school performance were related to the degree of dietary control and plasma phenylalanine values.

RESULTS

The IQ scores at 5 years of age were 100 +/- 10.8. Continued evaluation showed that IQ scores remained unchanged. Poor school performance was twice as frequent as in general population; the deficit in the IQ score of this group was 8 points below that of normal sibs. There was no correlation between plasma phenylalanine and the IQ score after the age of 5 years. The positive control decreased with aged.

CONCLUSIONS

Children with typical PKU have an IQ deficit relative to their normal sibs just before relaxing treatment. Good dietary control until 5 years of age, maternal intelligence and continuing evaluation during relaxing diet are the best conditions for optimal intellectual progress. There is no evidence that continued treatment during adolescence is beneficial.