Symphalangism, Proximal, 1b, also known as sym1b, is related to multiple synostoses syndrome 2 and brachydactyly, type a1, c. An important gene associated with Symphalangism, Proximal, 1b is GDF5 (Growth Differentiation Factor 5). Affiliated tissues include bone, and related phenotypes are pes planus and clinodactyly of the 5th finger