Abnormal organic acidurias in mentally retarded patients.

Urine specimens from 1778 mentally retarded patients and 420 age and sex matched non-retarded controls selected from a general practice have been analysed for non-amino organic acids by a quantitative extraction and gas chromatographic method. The compounds were identified by combined gas chromatography and mass spectrometry. Approximately 5% of the patients had an abnormal organic aciduria. The frequency of abnormalities was slightly higher (about 7%) in a group of 248 severely subnormal children, but not in cases with a family history of mental retardation, retarded sibs, or whose parents were consanguineous. The most frequently observed abnormalities were phenylalanine metabolites in cases of phenylketonuria (about 1%), increased excretion of benzoic acid (about 1%), and increased excretion of 2-oxoglutaric acid with or without raised urinary citric-acid levels (about 1%). The biochemical and clinical significance of these findings is being further investigated.