proximal symphalangism proximal symphalangism 2 MIM:615298 A proximal symphalangism that is characterized by absence of the cuboid bone and lack of shortness of the first and fifth metacarpal bones, and the presence of distal interphalangeal joint fusions and flat feet and that has_material_basis_in heterozygous mutation in the GDF5 gene on chromosome 20q11. disease_ontology DOID:0080788