synpolydactyly synpolydactyly synpolydactyly is a joint presentation of syndactyly (fusion of digits) and polydactyly (production of supernumerary digits). this is often a result of a mutation in the hox d13 gene. synpolydactylyother namesorthopedic types omim name gene 186000 spd1 hoxd13 608180 spd2 fbln1 610234 spd3 ? at 14q11.2-q12