Brachydactyly type A2 (Mohr-Wriedt type)
Brachydactyly type A2 or Mohr-Wriedt type is characterised by hypoplasia/aplasia of the second middle phalanx of the index finger, second toe and sometimes little finger. There is radial deviation of the index finger and tibial deviation of the second toe.
Type A2 brachydactyly can be caused by a mutation in the human bone morphogenetic protein receptor 1B gene (BMPR1B) on chromosome 4q, that affect cartilage formation. It is an autosomal dominant inheritable disease.
Affected middle phalanx appears triangular or rhomboid in shape and it is called as "delta phalanx". The delta phalanx has a continuous epiphysis, running from the proximal to the distal end of the phalanx along the shortened side. Thus, growth can occur only outward leading to persistent angulations and little gain in length.