X-linked mental retardation associated with bilateral clasp thumb anomaly

We report on a family in which mental retardation is associated with a bilateral clasp-thumb anomaly (absent extensor pollicis brevis tendons). Males over 3 generations were documented to have this combination of findings and pedigree analysis strongly suggests X-linked inheritance. We are not aware of previous reports of X-linked mental retardation (XLMR) associated with this anomaly. There was no evidence of a fragile X in the 2 brothers who were studied for this abnormality.