Syndactyly is one of the most common congenital malformations of the hands and feet， characterized by softissue or bony fusion between adjacent digits， and clinically categorized into isolated and syndromic forms. Based on clinical phenotypes and molecular-genetic evidence， isolated syndactyly has been classified into nine categories comprising sixteen subtypes. Prior studies have largely focused on case reports， identification of causative genes， or phenotypic overviews， whereas systematic developmental-biology interpretations of its molecular pathology remain limited. This review integrates key processes in limb development， including early limb bud formation， patterning of the proximodistal and anteroposterior axes， and molecular regulation of interdigital programmed cell death. Furthermore， the pathogenic pathways and key nodes involved in syndactyly across 3 themes are delineated： the WNT-FGF8 axis， the SHH-BMP axis， and retinoic acid signaling together with apoptosis and extracellular matrix remodeling. The article holds that syndactyly fundamentally reflects a failure in the closure of the interdigital morphogenetic window. Its molecular basis lies in the disruption of the temporal coordination by developmental signals that govern tissue fate transition， programmed cell death， and extracellular matrix clearance. This framework may provide a new theoretical basis for the precise classification and etiological interpretation of the disorder.

 , Syndactyly, Limb development, WNT-FGF8 axis, SHH-BMP pathway, Retinoic acid