We recruited a series of 45 male patients and 49 female patients with sporadic nonsyndromic mental retardation, including 63 French Canadians, 6 European whites, 9 non-European whites, 2 South Americans, 6 nonwhites, and 8 patients of mixed race or ethnic background. We used a series of open-ended questions to determine race or ethnic background by asking the parents of the patients about the origin of each of their parents. The diagnosis of mental retardation was made on a clinical basis with the use of standardized developmental or IQ tests.
