Summary

Brachydactyly type B (BDB) is a very rare congenital malformation characterized by hypoplasia or aplasia of the terminal parts of fingers 2 to 5, with complete absence of the fingernails. Prevalence is unknown but only a few cases have been reported in the literature. The thumbs are always intact but frequently show flattening, splitting or duplication of the distal phalanges. Digits on the radial side of the hand are less severely affected than those on the ulnar side. The feet are similarly affected but less severely. Soft tissue syndactyly, symphalangism, carpal and/or tarsal fusions and shortening of metacarpals and/or metatarsals may be present. An autosomal dominant pattern of inheritance has been reported and in the majority of cases, BDB is caused by mutations in the receptor kinase-like orphan receptor 2 gene (ROR2) on 9q22.