Biochemical screening for inherited metabolic disorders in the mentally retarded

A biochemical screening programme for the detection of inherited metabolic disease was carried out on urine and blood samples from inmates of the Alexandra Institute for the mentally retarded, Cape Town. Of the 1087 patients screened, positive results for phenylketonuria were obtained in 3, for cystinuria in 2 and for Hartnup disease in 1. The overall frequency of metabolic disorders was 0,6%. It is evident that genetic metabolic disease as detected by current screening procedures makes only a small contribution to the overall burden of mental retardation.