Brachydactyly type A2

Alternate names

BDA2; Mohr-Wriedt type brachydactyly; Brachymesophalangy 2

Definition

Brachydactyly type A2 is a very rare condition affecting the middle bone (middle phalanx) of the index finger and the second toe.

Epidemiology

A very rare digital malformation. No epidemiologic studies available. Reported pedigrees are summarized in OMIM.

Cause

• Type A2 brachydactyly can be caused by mutation in the human bone morphogenetic protein receptor 1B gene (BMPR1B) on chromosome 4q, that affect cartilage formation in a dominant-negative manner..
• Kjaer et al. found that sparing of the 4th finger distinguishes the Mohr-Wriedt type BDA2 from BDA2 caused by mutations in BMPR1B and concluded that the growth and differentiation factor 5 gene (GDF5) on chromosome 20q11 is a novel BDA2 causing gene.
• Mutations in GDF5 alter the receptor binding affinities and can also cause symphalangism.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

• In families with multiple cases of brachydactyly type A2, it seems that the condition is inherited in an autosomal dominant manner.
• This means that every child of a person affected by the condition has a 50% chance of having the condition themselves.

Signs and symptoms

• BDA2 is characterized by hypoplasia/aplasia of the 2nd middle phalanx of the index finger and sometimes little finger. It was first described by Mohr and Wriedt .
• Characteristically, affected individuals have a triangular-shaped middle phalanx in the index fingers and second toes.
• In severely affected cases, the index finger is curved radially.
• Deformity of the 2nd toe is a more consistent finding than deformity of the index finger.
• The big toes show malformation of the proximal phalanx resulting in fibular deviation of the distal phalanx, while all other toes have rudimentary middle phalanges causing tibial deflection of their distal phalanges.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Type A2 brachydactyly(Short index fingers and second toes)

30%-79% of people have these symptoms

• Clinodactyly of the 5th finger(Permanent curving of the pinkie finger)
• Short foot(Short feet)

5%-29% of people have these symptoms

• Aplasia/Hypoplasia of the middle phalanx of the 2nd finger(Absent/small middle index finger bone)
• Short 2nd metacarpal(Shortened 2nd long bone of hand)
• Short middle phalanx of the 5th finger(Short middle bone of the little finger)

Diagnosis

Clinical evaluation of the hands and curved index finger, together with the second toe, also seen in X-rays. This is seen as triangular shaped middle phalanx of the index fingers and second toes..

Treatment

There is no specific management or treatment that is applicable to all forms of brachydactyly. Plastic surgery is only indicated if the brachydactyly affects hand function or for cosmetic reasons, but is typically not needed. Physical therapy and ergotherapy may ameliorate hand function..

Prognosis

Prognosis for the brachydactylies is strongly dependent on the nature of the brachydactyly, and may vary from excellent to severely influencing hand function. If brachydactyly forms part of a syndromic entity, prognosis often depends on the nature of the associated anomalies.

NIH genetic and rare disease info

• NIH info on Brachydactyly type A2

Brachydactyly type A2 is a rare disease.

Brachydactyly type A2 Resources
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