[Phenylketonuria: a children's disease in adulthood]

The prognosis for patients with phenylketonuria (PKU) has improved greatly with early institution of treatment after birth. It was assumed that the diet could be terminated after adolescence but there are strong indications that hyperphenylalaninaemia can have detrimental effects in adult patients. Hyperphenylalaninaemia can cause reversible white matter abnormalities, and is also associated with psychiatric illness, which improves with lowering of the plasma phenylalanine level. Even optimally treated patients generally have a decreased performance with neuropsychological tests compared with subjects without PKU. Elevation of the plasma phenylalanine level leads to worsening of neuropsychological performance, lowering of the level leads to improved performance. Strict metabolic control is necessary during pregnancy in women with PKU in view of the increasing frequency of congenital abnormalities with increasing phenylalanine level. The complexity and demanding nature of the diet treatment make specialised facilities for optimal medical and paramedical care mandatory.