Preaxial polydactyly type 4: variability in a large kindred.

A five generation family with type 4 preaxial polydactyly is reported. The 21 affected individuals demonstrated variability in expression without apparent sex influence and penetrance which was complete. The deformities were more severe in the feet than the hands. Anteroposterior flatness of the thumbs was the only manifestation of the trait in the hands of several affected family members.