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Polydactyly

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This article is about the human congenital disorder (disease). For the paleontological application, see Dactyly.

Left foot with postaxial polydactyly of 5th ray

Right foot with postaxial polydactyly of 5th ray

Photograph of the left hand of a 27-year-old man. The supernumerary thumb had normal sensation; with no joints, it could not move independently.

Image:Polydactyl.jpg

Polydactyly, or polydactylism, also known as hyperdactyly, is the anatomical variant consisting of more than the usual number of digits on the hands and/or feet. It is a congenital abnormality, usually genetically inherited as an autosomal dominant trait. When each hand or foot has six digits, it is sometimes called hexadactyly.

Polydactyls have six or more digits on their hands or feet. The extra digits vary from small pieces of soft tissue to apparently complete digits. In Western societies, they are usually surgically removed during early life, but not always.

The condition is reported in about 1 child in every 500, although the frequency varies greatly from population to population. It is higher in some groups (an example is the Amish in the United States) due to the founder effect.

Range of motor skills in these extra digits is hard to chart given the rarity of the condition, but cases have varied. In some cases, the extra digit has no joints in the bone and thus is completely immobile, in other cases the extra digit has limited dexterity, and some cases have been reported in which an extra finger was fully functional, and indistinguishable from the rest of the fingers.

Historically and in the contemporary world, polydactylyism has been associated with witchcraft, psychic power, the extraterrestrial, divine connection, and sporting prowess.

Nowadays, reactions to polydactylyism is mixed. Although the condition is usually not life-threatening or even particularly debilitating, most people in Western societies have the extra digits removed surgically. However, there are other people who enjoy the physical distinction.

[edit] Types of polydactyly

There are several types of polydactyly, of varying frequency. Here are some of them:

Polydactyly with cleft lip/palate and psychomotor retardation (Varadi-Papp Syndrome)
Polydactyly myopia syndrome
Polydactyly postaxial dental and vertebral
Polydactyly postaxial with median cleft of upper lip
Polydactyly postaxial
Polydactyly preaxial type 1
Polydactyly syndrome middle ray duplication
Polydactyly visceral anomalies cleft lip palate