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KEY POINTS
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Key Points

  • Defined as the presence of a hand or foot with more than 5 digits.

  • May be “radial/tibial” (formerly preaxial), “ulnar/fibular” (formerly postaxial), or “central”.

  • Incidence is 1/100 to 1/698 depending on ethnic origin of population studied.

  • Major consideration is to determine if isolated or associated with other anomalies. Isolated polydactyly is frequently inherited as an autosomal dominant condition.

  • Polydactyly is a component of at least 119 recognized conditions.

  • Differential diagnosis includes trisomy 13, Meckel–Gruber syndrome, Bardet-Biedl syndrome, Ellis–van Creveld syndrome, short-rib polydactyly syndrome, and Smith–Lemli–Opitz syndrome.

  • Refer for detailed fetal sonographic anatomic evaluation, consider karyotype.

  • Surgical outcome and prognosis are good if isolated.

  • If associated with other anomalies, consider genetics consultation and DNA mutation testing.

  • Recurrence risk depends on underlying diagnosis.

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CONDITION
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Polydactyly is the presence of a hand or a foot with more than five fingers or toes. Although the medical term polydactyly was first ascribed to the 17th century Amsterdam physician Theodor Kerckring (Blauth and Olason, 1988), the presence of polydactyly was mentioned in the Bible (Nicolai and Schoch, 1986) and is even evident on the left leg of St. Joseph in Raphael’s famous 16th century painting of “The Marriage of the Virgin” (Mimouni et al., 2000). Polydactyly is the most frequent congenital anomaly of the human hand (Tsukurov et al., 1994). Polydactyly affecting the thumb or great toe is now classified as “radial/tibial” (formerly preaxial), which refers to a duplication of digits on the radial side of the hand and the tibial side of the foot, or “ulnar/fibular” (formerly postaxial), in which the extra digits occur on the ulnar and fibular sides of the hand and foot, respectively (Talamillo et al., 2005). Cases in which the three central digits are affected are referred to as “central polydactyly” and are the least common of the three types. In general, radial/tibial polydactyly is more common than ulnar/fibular polydactyly (Temtamy and McKusick, 1978). Polydactyly has been further subclassified on a descriptive basis. In ulnar/fibular polydactyly, type A denotes fully developed extra digits. Type B describes rudimentary extra digits or a pedunculated skin tag that is usually found on the hands and only rarely on the feet. This type is very common among blacks. In radial/tibial polydactyly, when the thumb is polydactylous it is known as type I, when a triphalangeal thumb is present it is known as type II, when the index finger is polydactylous it is type III, and when polysyndactyly occurs it is known as type IV.

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Morphogenetically, the hand and foot malformations can be considered as a process of bifurcation of one or several finger or toe rays in the longitudinal axis progressing from peripheral to central. Segment polarity genes initially identified in Drosophila, such as sonic hedgehog (SHH), play a critical role in this process.

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INCIDENCE
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