Prevalence of Homocystinuria Among the Mentally Retarded: Evaluation of a Specific Screening Test

The prevalence of homocystinuria in patients with mental retardation institutionalized in the United States is about 0.02%; this is lower than a previous estimation from Northern Ireland (0.3%). On the other hand, about 5% of patients with dislocated lenses may be expected to have the disease. A silver-nitroprusside test which is almost completely specific for homocystine has been evaluated. It should be useful for screening.