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.
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.