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Left foot with postaxial polydactyly of 5th ray

Right hand with mid-ray duplication

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.

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, or hexadactylism.

The extra digit is most often a small piece of soft tissue; occasionally it might contain bone but no joints; rarely it may be a complete, functioning digit. The extra digit is most common on the ulnar (little finger) side of the hand, less common on the radial (thumb) side, and very rarely within the middle three digits. The extra digit is most commonly an abnormal fork in an existing digit, or it may rarely originate at the wrist like a normal digit does.

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.

Historically and in the contemporary world, polydactylyism has been associated with witchcraft, psychic power, the extraterrestrial, divine connection, and sporting prowess.^{[citation needed]}

Nowadays, reactions to polydactylyism are 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.

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

• Dactyly
• List of polydactyl people
• Polydactyl cat
• Polycephaly
• Polymelia (= extra limbs)
• Supernumerary body part

• Polydactyly and Syndactyly
• Polydactylism FAQ
• Polydactyly Blogger