The use of a low phenylalanine diet with amino acid supplement in the treatment of behavioural problems in a severely mentally retarded adult female with phenylketonuria.

If phenylketonuria is untreated in infancy, it causes irreversible brain damage. No dietary treatment can alter this brain damage. However, it has been shown that dietary treatment can reduce behaviour disturbances often associated with the condition. In this study, a subject's behaviour was monitored over 18 weeks while on a low phenylalanine diet. Results demonstrate a significant reduction in the level of her disturbed behaviour.