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Polydactyly of hand in Infant/Neonate
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Polydactyly of hand in Infant/Neonate

Contributors: Michael Catanzaro MD, Danielle Wilbur MD
Other Resources UpToDate PubMed


Causes / typical injury mechanism:
  • Polydactyly of the hand is inherited. This may be a sporadic genetic mutation or may have an autosomal dominant inheritance pattern with variable penetrance.
  • Sonic hedgehog (SHH) / zone of polarizing activity pathways regulate anterior / posterior (ulnoradial) development.
  • Currently 6 genes have been identified as contributing to polydactyly of the hand: ZNF141, GLI3, MIPOL1, IQCE, PITX1, and GLI1.
Classic history and presentation: Polydactyly is present at birth with various degrees of maturity of the accessory digit(s).

Prevalence: There is a male prevalence for both preaxial (thumb duplication) and postaxial (ulnar digit) polydactyly.

Risk factors:
  • Preaxial polydactyly has a higher prevalence in White individuals.
  • Postaxial polydactyly has a 10 times higher prevalence in Black individuals with an autosomal dominant inheritance pattern. White patients with postaxial polydactyly need genetic work-ups.
  • The limb bud forms from ectoderm with underlying mesoderm. Limb development takes place in weeks 4-8 of gestation.
  • The zone of polarizing activity is an area of mesenchyme beneath the apical ectodermal ridge on the posterior aspect of the limb bud.
  • Via secretion of SHH, there is development of the limb in the ulnoradial dimension.
  • Oversecretion of SHH results in postaxial polydactyly. Ectopic SHH expression or disruption of this signaling pathway leads to preaxial polydactyly.
Grade / classification system:
  • Postaxial polydactyly –
    • Type A: well-formed digit
    • Type B: rudimentary digit
  • Preaxial polydactyly (thumb duplication) – Wassel classification
    • Type I: bifid distal phalanx
    • Type II: duplicated distal phalanx
    • Type III: bifid proximal phalanx
    • Type IV (most common): duplicated proximal phalanx
    • Type V: bifid metacarpal
    • Type VI: duplicated metacarpal
    • Type VII: triphalangism


Q69.0 – Accessory finger(s)
Q69.1 – Accessory thumb(s)

81793007 – Polydactyly of fingers

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Last Reviewed:12/13/2022
Last Updated:02/09/2023
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Polydactyly of hand in Infant/Neonate
Copyright © 2024 VisualDx®. All rights reserved.