Brachydactyly, Type B1

Alternative Names

  • BDB1
  • Brachydactyly, Type B
  • BDB
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WHO-ICD-10 version:2010

Congenital malformations, deformations and chromosomal abnormalities

Congenital malformations and deformations of the musculoskeletal system

OMIM Number

113000

Mode of Inheritance

Autosomal dominant

Gene Map Locus

9q22.31

Description

Brachydactyly type B (BDB) is an autosomal recessive skeletal disorder characterized by the absence or underdevelopment of terminal phalanges. Typical features of the condition include hypoplasia or aplasia of distal phalanges and nails, short middle phalanges, and deformed thumbs and big toes. The condition shows wide-ranging phenotypic variability ranging from a mild version characterized by slightly shortened distal phalanges and nails, and frequent distal symphalangism, to severe forms characterized by amputation-like phenotype with absence of distal phalanges and/or nails of fingers. The most severe form of BDB includes severe skeletal defects primarily affecting the distal limbs and the spine and resembles the clinical features of Robinow Syndrome. Interestingly, both Robinow Syndrome and BDB are caused due to defects in the same gene.

Loss of function mutations in the ROR2 (Receptor Tyrosine Kinase Like Orphan Receptor 2) gene are responsible for the phenotypic effects of BDB. Although it is known that the ROR2 protein is involved in protein-protein interactions, its exact function and its role in the development of BDB is not known. It is speculated that the protein may be involved in the formation of chondrocytes, and thus play a role in cartilage and growth plate development. Furthermore, studies have been performed on the genotype-phenotype correlations of ROR2 and BDB, and it has been shown that distal mutations on the gene tend to cause more severe phenotypes.

Epidemiology in the Arab World

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Other Reports

Jordan

Hamamy et al. (2006) reported on a 29-year old Jordanian male, who presented with marked shortening of fingers (except thumb) with absence of nails. Fingers III-V had bulbous finger tips, and toes II-V had hypoplastic nails. Thumbs and big toes were normal. The patient was born to non-consanguineous healthy parents, and also had three normal siblings (confirmed radiographically). However, he was married to his first cousin, and his 3-year old son was similarly affected. In addition, the patient also showed a prominent nose, high nasal bridge, hypoplastic ala nasi, and high arched palate; all typical of BDB. Genetic analysis proved the presence of a de novo heterozygous mutation in the patient in the ROR2 gene.

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