PKU is one of the most frequent inherited metabolic disorders, with a prevalence of about one in 14,000 babies in populations of European descent. The disorder (caused by mutations within the gene for the enzyme phenylalanine hydroxylase), results in a failure to convert phenylalanine to tyrosine in the liver. The accumulation of phenylalanine prevents normal postnatal brain development and leads to severe learning difficulties. Screening at birth to identify individuals with the disorder, and regulation of blood concetrations of phenylalanine by a low-protein diet in affected children can result in normal cognitive functioning in adulthood.

John Walter from the Royal Manchester Childrens Hospital, UK, and colleagues assessed data from 4 PKU centres (three in the UK and one from Australia) to estimate the adherence to PKU control among younger and older children. Children younger than 10 years had substantially fewer phenylalanine concentrations above the recommended limit for PKU control compared with children older than 15 years (30% compared with 80%, respectively). Similar results were observed for the frequency of blood testing; more than 80% of children younger than 10 years had the recommended frequency of blood testing, compared with less than half of children aged 15 years or older.

John Walter comments: "Our findings indicate that adolescents and young adults generally do not comply with recommendations for the monitoring and control of phenylalanine concentrations. If phenylketonuria is proven to be dangerous in adults as it is in infants, maintenance of good dietary control beyond childhood will become increasingly important, and more acceptable modes of treatment than available will need
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Contact: Richard Lane
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Lancet
4-Jul-2002