Brachydactyly, Type B1; BDB1

What is Brachydactyly, Type B1; BDB1?

Brachydactyly, Type B1; BDB1 is a rare disease. It is also known as Apical dystrophy BDB1 BDB2 Brachydactyly - type B2 Brachydactyly, Type B; Bdb.

Also called an apical dystrophy, the extent of the changes can vary even within the same pedigree. The terminal portion of the index to the 5th fingers show absent or rudimentary nails and the toes show a similar pattern. The big toes and thumbs are spared. Syndactyly and symphalangism can occur and the mildest expression of the gene might be the fusion of the proximal and distal phalanges. Houlston and Temple (1994) reported a family with what seemed like a characteristic face. There was a high nasal bridge, a prominent nose with a bulbous tip, hypoplastic alae nasi, widely spaced eyes with downslanting palpebral fissures and a short philtrum. Santos et al., (1981) and Santos (1995) also reported a family where affected individuals had a prominent nose with a bulbous configuration. de Ravel et al., (1999) reported a brother and sister with brachydactyly type B with similar facial features to other reported patients. The parents had no clinical abnormalities. Gonadal mosaicism was suggested. The brother had markedly bulbous finger tip pads and nail aplasia. The authors suggest that brachydactyly type B and Cooks (1985) (qv) syndrome are identical abnormalities.
Gong et al., (1999) mapped the gene to 9q in two families. Oldridge et al., (1999) also presented evidence of linkage to 9q22. Slavotinek and Clayton-Smith (1999) report a further case and review syndromes with similar digital abnormalities. Oldridge et al., (2000) demonstrated mutations in the ROR2 gene. This codes for a tyrosine kinase receptor. There were two nonsense and one frameshift mutation within a 7-amino-acid segment of the 943-amino-acid protein, suggesting gain of function mutations. Schwabe et al., (2000) reported further mutations in the ROR2 gene in this condition.
Six families without ROR2 mutations were studied by Lehmann et al., (2007). Mutations in 5 were found in the bone morphogenetic protein antagonist NOGGIN. The patients had a distinct phenotype - a severe transverse distal reduction, with fingers I and II less severely affected. In those with distal phalanges present, there were abnormal proximal interphalangeal joints (they could not bend these and flexion creases were missing). Proximal symphalangism and carpal synostosis and partial cutaneous were almost constant features. The authors call this 'brachydactyly type B2'.
There have been patients (with ROR2 mutation) with in addition to the Robinow phenotype, brachydactyly type B (see elsewhere) - Schwarzer et al., (2009).

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* This information is courtesy of the L M D.

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What gene changes cause Brachydactyly, Type B1; BDB1?

The syndrome is inherited in the following inheritance pattern/s:

Autosomal Dominant - In the case of autosomal dominant inheritance, just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation.

In some cases, a genetic syndrome may be the result of a de-novo mutation and the first case in a family. In this case, this is a new gene mutation that occurs during the reproductive process.

OMIM Number - 113000 (please check the OMIM page for updated information)

The syndrome can be caused by mutations in the following gene/s location/s:
ROR2 - 9q22.31

What are the main symptoms of Brachydactyly, Type B1; BDB1?

The typical symptoms of the syndrome are:
Micropenis, Joint contracture of the hand, Hemivertebrae, Hypoplastic sacrum, Short toe, Short middle phalanx of finger, Short distal phalanx of finger, Autosomal dominant inheritance, Syndactyly, Wide anterior fontanel, Broad thumb, Aplasia/Hypoplasia of the distal phalanges of the hand, Anonychia, Aplasia/Hypoplasia of the distal phalanges of the toes, Abnormality of the metacarpal bones, Abnormality of thumb phalanx, Abnormality of the foot, Synostosis of carpal bones, Type B brachydactyly, Short long bone, Thoracolumbar scoliosis, Vertebral fusion, Ventricular septal defect, Symphalangism affecting the phalanges of the hand, Camptodactyly, Preaxial foot polydactyly, Cutaneous finger syndactyly, Delayed eruption of permanent teeth, Delayed cranial suture closure

How does someone get tested for Brachydactyly, Type B1; BDB1?

The initial testing for Brachydactyly, Type B1; BDB1 can begin with facial genetic analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the type of genetic testing needed. A consultation with a genetic counselor and then a geneticist will follow.

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.

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