GDF6 and osteoarthritis: Mutations and/or deletion of the effector genes BMP2, BMP6, BMPR1B, GDF6 and GDF5 have been associated with brachydactyly (BMP2, BMPR1B and GDF5)19–21, joint deformities and osteoarthritis (GDF5)22, reduction in long bone size (BMP6)23, joint defects (GDF5 and GDF6) and severe chondrodysplasia (BMP2)24.