The natural history of untreated phenylketonuria over 20 years.

Fifty-one adults with untreated phenylketonuria (PKU), have been reviewed after a 20 year interval, at ages ranging from 28.8 to 71.8 years. Five died of causes unrelated to PKU. Three severely affected individuals had shown a progressive loss of motor function and three had developed epilepsy, bringing the total with this problem to 12. No loss of abilities was apparent in 41 patients. Other health problems, including cataracts, were not frequent. Serum phenylalanine levels had decreased over the 20 year period. Untreated PKU does not generally cause progressive loss of abilities during adult life.