HOXD13 and synpolydactyly type 1: Most non-syndromic synpolydactyly cosegregates with a mutation in the HOXD13 gene on chromosome 2q31 and is categorized as Synpolydactyly type 1 (SPD1, OMIM 186000), which is also known as syndactyly type II (SD II), according to the nomenclature of Temtamy and McKuisck (Temtamy and McKusick, 1978).