Cystinuria and its relationship to mental retardation.

Urine specimens from 2,073 mentally retarded children have been analysed for their amino acid content, with the aim of determing the relationship of cystinuria and mental retardation. No children homozygous for cystinuria were identified, but 50 heterozygous children were found. This heterozygote incidence is 13 times that expected in our general population.