Polydactylism (polydactyly, hyperdactyly) is a birth defect, a condition characterized by the presence of one or more extra fingers or toes.
An abnormality called polydactylism includes an extra digit of the upper, lower limbs or both. It is estimated that about 2 per 1000 children are born with an extra finger/toe.
Polydactylism is associated with different mutations in a genetic material or a regulatory that influence on the genes. It was estimated that around 39 mutations that may cause polydactylism. Polydactylism may be the sole defect or a symptom of other disorders such as Rubenstein-Taybi Syndrome, Pallister-Hall Syndrome, Mohr Syndrome, Meckel Gruber Syndrome, Ellis van Crevald Syndrome and Biemond Syndrome. The syndromes associated with ulnar polydactyly are: Greig cephalopolysyndactyly syndrome, Meckel syndrome, Ellis–van Creveld syndrome, McKusick–Kaufman syndrome, Down syndrome, Bardet–Biedl syndrome, Smith–Lemli–Opitz syndrome. Mutations in Hoxa- or Hoxd clusters are known to cause polydactylism. Radial polydactyly is associated with the next syndromes: Holt–Oram syndrome, Fanconi anemia, Townes–Brocks syndrome, and Greig cephalopolysyndactyly (also occurs with ulnar polydactyly). The Bardet–Biedl syndrome, Meckel syndrome, Pallister–Hall syndrome, Legius syndrome, Holt–Oram syndrome, syndactyly and cleft hand are associated with central polydactyly.
The 4th week of embryologic period is critical for the development of the limbs. Toxic or radiation influence on the fetus in this period can cause the formation of birth abnormalities. The family history of polydactylism puts the offspring at risk of inheritance of the abnormality or a syndrome that involves polydactylism.
[See also: Atrial septal defect]
The extra finger or toe is a piece of soft tissue, although sometimes it contains bone tissues without joints. Commonly the extra digit is present on the side of the little finger (ulnar side). Rarely the extra digit appears in the central area of the palm (ring, middle and index fingers). Usually the extra digit originates from the normal finger and rarely begins from the wrist or a foot. The presence of the extra digit on the ulnar side of the hand is called postaxial polydactyly. The occurrence of the extra digit on the side of the thumb is called preaxial polydactyly.
The extra digit may vary from the skin tag to the complete duplication and the complete developed digit either small or normal-size. Commonly the extra finger is rudimentary and consists of an end phalanx with a nail. There are no tendons present in the extra digit.
To evaluate the diagnosis the X-ray is performed. As long as polydactyly is associated with several inborn diseases the affected child should be carefully examined and consulted with a genetic specialist.
The condition is not life-threatening. Surgical removal of the extra finger or toe during infancy is a preferable treatment, although the extra digit may remain.