The use of a low phenylalanine diet in response to the challenging behaviour of a man with untreated phenylketonuria and profound learning disabilities.

If phenylketonuria (PKU) is not treated from an early age with a reduced phenylalanine diet, irreversible brain damage may occur. Although dietary intervention can do nothing to alter this impairment once it occurs, there is some evidence to suggest that a low phenylalanine diet may help to reduce the level of behavioural disturbances frequently experienced by people with untreated PKU. Using this evidence, dietary intervention was used in response to the challenging behaviour of a 30-year-old man with profound learning disabilities. Initial improvements were observed, but overall the results were inconclusive. Possible confounding factors are discussed. An unusual reaction to neuroleptic medication whilst on the diet is also documented.