Although both preaxial polydactyly and syndactyly are cardinal features of this malformation, it is classified as a form of polydactyly because syndactyly does not occur in the absence of polydactyly (McClintic, 1935), the opposite not being true. On the other hand, polysyndactyly is here classified as a type of syndactyly because polydactyly (of the third or fourth fingers and fifth toes) does not occur in the absence of syndactyly. The thumb shows only the mildest degree of duplication, and syndactyly of various degrees affects fingers 3 and 4. The foot malformation is more constant and consists of duplication of part or all of the first or second toes and syndactyly affects all of the toes, especially the second and third. [from
OMIM]