Brachydactyly type B2

Brachydactyly type B2 (BDB2) is a very rare inherited skeletal disorder characterized by shortening or absence of the terminal phalanges (end bones) of the fingers and toes, with partial or complete absence of the nails. It is a subtype of brachydactyly type B and is distinguished by the additional presence of partial duplication (bifurcation or symphalangism) of the distal phalanges, particularly of the thumbs and great toes. The condition primarily affects the skeletal system of the hands and feet, and the degree of severity can vary considerably even within the same family. Clinically, individuals with BDB2 typically present with hypoplasia or aplasia of the distal phalanges of the second through fifth digits, which gives the fingers a shortened or stubby appearance. The thumbs and great toes may show broad or bifid (split) terminal phalanges, which is a hallmark distinguishing feature from classic brachydactyly type B1. Nail abnormalities, including absent or rudimentary nails, are commonly observed on the affected digits. The condition is caused by heterozygous mutations in the NOG gene (noggin), located on chromosome 17q22, which encodes a protein involved in bone morphogenetic protein (BMP) signaling — a critical pathway in skeletal development. Brachydactyly type B2 is present from birth and is typically identified during infancy or early childhood. The condition does not usually affect life expectancy or cognitive function. There is no specific curative treatment; management is primarily supportive and may include orthopedic evaluation, occupational therapy to optimize hand function, and in some cases surgical intervention to improve digit function or cosmetic appearance. Genetic counseling is recommended for affected families given the autosomal dominant inheritance pattern.

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