GDF5 and brachydactyly type A2: Brachydactyly Type A2 (BDA2), an autosomal dominant disorder characterized by malformations of the middle phalanges, is associated with mutations in Bmpr1b,468,469GDF5,468,470,471 and BMP2. 472,473 Specific mutations in GDF5 (e.g., N445K/T) are also associated with synostosis syndrome,474 whereas duplications in the regulatory elements of BMP2472,475 contribute to BDA2 pathogenesis.473 In contrast, brachydactyly type-B (BDB), which is marked by terminal digit deficiencies, arises from point mutations in Noggin476 (Table 6).