Phenylketonuria presenting in adulthood as progressive spastic paraparesiswith dementia

A 57 year old woman living independently in the community presented with fo ur years of progressive spastic paraparesis and dementia. An extensive eval uation for the usual causes of these difficulties was unrevealing, but her serum phenylalanine concentration was markedly elevated and genetic analysi s demonstrated mutations in the phenylalanine hydroxylase gene consistent w ith classic phenylketonuria. A protein restricted diet was associated with improvement in her condition. Although untreated phenylketonuria is typical ly associated with severe neurological dysfunction beginning in early child hood, this case shows that disability may be delayed until adulthood.