polydactyly, condition that is present at birth in which a person has more than five fingers on a hand or more than five toes on a foot. The term polydactyly is derived from the Greek words poly, meaning “many,” and daktylos, meaning “digit.” Polydactyly occurs in an estimated 1 in 500–1,000 births, with variation from 1 in roughly 1,330 births among white people to 1 in 143 births among Black people. In general, the condition affects males and females equally. Many children with polydactyly are otherwise healthy individuals.

　　Polydactyly can present in various ways: in some instances, an extra digit is visible as a small bump (or “nubbin”), whereas in other instances, the digit is a fully functioning extra finger or toe. Rarely, individuals are born with extra digits on both the hands and the feet. Often the extra digit is made up of skin and soft tissue and may include a bone. More-complex cases of polydactyly involve a combination of skin, soft tissue, and bone, along with a joint, ligament, or tendon.

　　Britannica Quiz 44 Questions from Britannica’s Most Popular Health and Medicine Quizzes Types and causes of polydactyly Polydactyly can be divided into three types: preaxial, central, and postaxial. Preaxial polydactyly is characterized by the duplication of the thumb or big toe. Central polydactyly is characterized by an additional digit near the middle digits, such as between the second and third toe or the third and fourth toe or between the index and middle finger or the middle and ring finger. Postaxial polydactyly is characterized by an extra little toe or finger (the “pinkie” toe or finger). In any type of polydactyly, the extra digit may appear as a lone symptom of so-called non-syndromic polydactyly, or it may occur as syndromic polydactyly, in which it accompanies other congenital anomalies as part of a syndrome (e.g., polysyndactyly [polydactyly with webbing between or fusion of adjacent digits], Down syndrome, or trisomy 13).

　　The underlying pathophysiology of polydactyly is not fully known. In some instances, the condition appears to be inherited. For example, in some persons, polydactyly is a dominant trait, meaning that if one of an individual’s biological parents carries the affected gene, the individual has a 50 percent chance of being born with the condition. Genetic disorders or environmental factors that disrupt limb growth during fetal development can cause polydactyly.

　　Treatment Polydactyly may be treated by tying off the extra digit; the digit shrivels and eventually falls off. This technique is not used when extra digits have a nerve, a vein, and an artery, since pain can result during digit removal. Tying off also carries a risk of incomplete removal, in which a neuroma (a painful bump) develops, because the body tries to regrow the nerve of the extra digit. In complex cases, extra digits are removed with surgery, typically when an individual is between ages one and two.