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Polydactyly or polydactylism (), also known as hyperdactyly, is a congenital physical anomaly in humans, dogs, and cats having supernumerary fingers or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes). ==Signs and symptoms== In humans/animals this condition can present itself on one or both hands. The extra digit is usually a small piece of soft tissue that can be removed. Occasionally it contains bone without 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. These are respectively known as postaxial (little finger), preaxial (thumb), and central (ring, middle, index fingers) polydactyly. The extra digit is most commonly an abnormal fork in an existing digit, or it may rarely originate at the wrist as a normal digit does. The world record holder for highest number of digits is Akshat Saxena from Uttar Pradesh, India. He was born in 2010 with 7 digits on each hand and 10 digits on each foot, for a total of 34 digits. The incidence of congenital deformities in newborns is approximately 2%, and 10% of these deformities involve the upper extremity. Congenital anomalies of the limb can be classified in seven categories, proposed by Frantz and O’Rahilly and modified by Swanson, based on the embryonic failure causing the clinical presentation. These categories are failure of formation of parts, failure of differentiation, duplication, overgrowth, undergrowth, congenital constriction band syndrome, and generalized skeletal abnormalities. Polydactyly belongs to the category of duplication. 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. Likewise if a syndrome is suspected or over 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Polydactyly」の詳細全文を読む スポンサード リンク
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