Brachydactyly type B

Definition

Brachydactyly type B (BDB) is a condition characterized by incomplete development (hypoplasia) or absence of the outermost bones of the fingers and toes (distal phalanges) and nails.

Epidemiology

This is a rare hand malformation with only a few published pedigrees in the world literature.

Types

There are 2 types of this condition, designated as type 1 and 2.

Cause

BDB type 1 is caused by mutations in the ROR2 gene. BDB type 2 is caused by mutations in the NOG gene.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

Inheritance of both types is autosomal dominant.

Signs and symptoms

• There is absence or hypoplasia of the terminal parts of the index to little fingers with complete absence of fingernails..
• The thumbs are always intact but frequently show flattening, splitting or duplication of the distal phalanges.
• Digits are less severely affected on the radial side of the hand compared to those on the ulnar side.
• The feet are similarly but less severely affected.
• The deformity is symmetric.
• There is soft tissue syndactyly, symphalangism, carpal and/or tarsal fusions and shortening of metacarpals and/or metatarsals.

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

• 2nd-5th toe middle phalangeal hypoplasia(Underdeveloped 2nd-5th middle toe bones)
• Absent fingernail
• Aplasia/Hypoplasia of the distal phalanges of the hand(Absent/small outermost finger bone of the hand)
• Short distal phalanx of finger(Short outermost finger bone)
• Short foot(Short feet)
• Short metacarpal(Shortened long bone of hand)
• Type B brachydactyly

30%-79% of people have these symptoms

• Absent phalangeal crease
• Aplasia/Hypoplasia of the distal phalanges of the toes(Absent/small outermost bones of toe)
• Aplasia/Hypoplasia of the middle phalanges of the hand(Absent/small middle finger bone of the hand)
• Aplasia/Hypoplasia of the middle phalanges of the toes(Absent/small middle bones of toe)
• Aplasia/Hypoplasia of the nails(Absent/small nails)
• Cutaneous finger syndactyly(Webbed fingers)
• Cutaneous syndactyly of toes(Webbed skin of toes)
• Proximal placement of thumb(Attachment of thumb close to wrist)
• Tarsal synostosis(Fused ankle bones)

5%-29% of people have these symptoms

• Broad hallux phalanx(Broad bone of big toe)
• Finger syndactyly
• Hypermetropia(Farsightedness)
• Sensorineural hearing impairment
• Symphalangism affecting the phalanges of the hand(Fused finger bones of the hand)
• Synostosis of carpal bones
• Fusion of wrist bones

1%-4% of people have these symptoms

• Carpal synostosis
• Distal symphalangism of hands(Fused outermost bones of hand)
• Proximal symphalangism of hands(Fused innermost hinge joints)
• Short 1st metacarpal(Shortened 1st long bone of hand)

Diagnosis

Clinical examination of the thumb anomalies and distal phalangeal hypoplasia, and absence of nails sometimes with associated distal symphalangism. Radiological examination of the hands and pattern profile analysis..

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 B

Brachydactyly type B is a rare disease.

Brachydactyly type B Resources
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