A clinical, cytogenetic and familial study of 307 mentally retarded, institutionalized, adult male patients with special interest for fra(X) negative X-linked mental retardation.

In this study we report the results of a systematic etiological, clinical genetic study in 307 institutionalized mentally retarded adult males. Special attention is paid to the nosology of X-linked mental retardation. During the survey 63 males with one or more 'Martin Bell'-like features were identified in whom repetitive fragile Xq27-3 screenings were negative. In 13 of them, belonging to 9 different families, pedigree data were compatible with X-linked inheritance. This finding confirms the existence of one (or more) forms of fra(x) negative mental retardation with 'Martin Bell'-like features.