Both proximal symphalangism (185800), which is due to mutations in the NOG gene (602991), and distal symphalangism (185700) are autosomal dominant disorders characterized by fusion of the proximal or distal interphalangeal joints, respectively. Kantaputra et al. (2002) described ... Both proximal symphalangism (185800), which is due to mutations in the NOG gene (602991), and distal symphalangism (185700) are autosomal dominant disorders characterized by fusion of the proximal or distal interphalangeal joints, respectively. Kantaputra et al. (2002) described a seemingly novel form of distal symphalangism. A Thai mother and son had brachydactyly, especially at the distal segment of the digits, fusion of the distal interphalangeal joints, and absence of digital phalanges 3 and 4. They also had cone-shaped epiphyses of middle phalanges 2 and 4, radial-ray carpal-bone anomalies, narrowing of the zygomatic arch, and dental pulp stones. The second fingers were predominantly affected. Proximal symphalangism was ruled out because of the pattern of the symphalangism and because no mutation in the NOG gene was found. Distal symphalangism shares many features with brachydactyly type B (113000), including aplasia/hypoplasia of the middle and distal phalanges of fingers 2 to 5 and fingernail dysplasia. This diagnosis was ruled out by the absence of mutation in the ROR2 gene (ROR2; 602337), which has been found in cases of type B brachydactyly.