Because there is an association between polydactyly and several syndromes, children with a congenital upper extremity deformity should be examined by a geneticist for other congenital anomalies. This should also be done if a syndrome is suspected, or if more than two or three generations of the family are affected. Research has shown that the majority of congenital anomalies occur during the 4-week embryologic period of rapid limb development. Polydactyly has been associated with 39 genetic mutations. More specific loci and genetic mechanisms responsible for disorders of duplications will be defined with time, as molecular research continues. Polydactyly can be divided into three major types, which are discussed below. Ulnar or postaxial polydactyly
This is the most common situation, in which the extra digit is on the ulnar side of the hand, thus the side of the little finger. This can also be called postaxial polydactyly. It can manifest itself very subtly, for instance only as a nubbin on the ulnar side of the little finger, or very distinctly, as a fully developed finger. Most commonly, the extra finger is rudimentary, consisting of an end phalanx with a nail, and connected to the hand with a small skin pedicle. Mostly one neurovascular bundle can be identified, with no tendons present in the extra digit. In case of a fully developed extra finger, the duplication usually presents itself at the level of the metacarpophalangeal joint. A triplication of the little finger is very rare. Ulnar polydactyly occurs ten times more often in African populations.
However, considering that this rumour first emerged in the 1580s from a Catholic dissenter, it is generally deemed false. Robert Chambers, purported author of Vestiges of the Natural History of Creation, and his brother William had six digits on each limb. Lucille Clifton, an African-American poet and civil rights advocate. Zerah Colburn, American prodigious math calculating savant. Calvin Choy, a Hong Konger singer and actor nicknamed "Sir One One" (Sir11) as he has six digits on his right hand. Several members of a Da Silva family in São Paulo, Brazil, have two thumbs on each hand. Vicente Fox, former President of Mexico, has six toes on each foot. Danny Garcia, boxing champion, has six toes on his right foot. Yoandri Hernández Garrido, nicknamed "Veinticuatro" ("twenty four" in Spanish), has six fully formed fingers on both hands and six perfect toes on each foot. Hampton Hawes, jazz pianist, was born with six fingers on each hand (the extra fingers were surgically removed shortly after birth). Henry II the Pious, High Duke of Poland 1238–1241, had six toes on his left foot. A boy named Hong Hong born in Pingjiang County, Hunan province, China, has 31 fingers and toes. Kamani Hubbard, a boy in California was born in 2009 with a rare case of polydactyly, with 12 fingers and 12 toes, all fully functional. Johann Jacob Freiherr von Moscon (1621–1661), Lower Styrian baron, is depicted with six fingers at his left hand on a portrait from Brežice, Slovenia.