On the inheritance of the split hand/split foot malformation.

Analysis of families with non-syndromal split hand/split foot (SHSF) confirms the existence of 2 distinct entities, most probably caused by at least 2 different autosomal dominant genes. In the families in which the SHSF malformation is non-syndromal and limited to the hands and feet (type I), the pattern of inheritance is of a regular autosomal dominant gene with a high penetrance (96%). In families in which at least one individual has other limb malformations and SHSF (type II), the transmission is often unusual. In most families, the gene is non-penetrant, sometimes for generations, before the birth of the first affected individual. Thereafter, among the descendants of affected individuals, the penetrance is reduced (66%), suggesting the possible existence of another gene which controls the appearance of the clinical manifestations. The possibility that SHSF associated with other limb malformations is a disorder caused by trinucleotide repeat instability is raised.