Congenital genetic anomaly in which extra fingers or toes, sometimes not completely developed, are present in an individual. There are two common forms of hexadactyly (6-digit polydactyly). In the autosomal dominant postaxial form, a single full or partial extra digit is located distal to the little finger. The GLI3 gene has been implicated. In the autosomal dominant preaxial form, a single full or partial extra digit is found proximal to the thumb. Both forms manifest during prenatal development. There are nine other less common forms, some with more than six digits; these latter are all very rare; aka polydactylism.