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. 2018 Nov 6:9:447.
doi: 10.3389/fgene.2018.00447. eCollection 2018.

Clinical Genetics of Polydactyly: An Updated Review

Muhammad Umair  1 , Farooq Ahmad  1 , Muhammad Bilal  1 , Wasim Ahmad  1 , Majid Alfadhel  2
Affiliations

Clinical Genetics of Polydactyly: An Updated Review

Muhammad Umair et al. Front Genet. .

Abstract

Polydactyly, also known as hyperdactyly or hexadactyly is the most common hereditary limb anomaly characterized by extra fingers or toes, with various associated morphologic phenotypes as part of a syndrome (syndromic polydactyly) or may occur as a separate event (non-syndromic polydactyly). Broadly, the non-syndromic polydactyly has been classified into three types, i.e.; preaxial polydactyly (radial), central polydactyly (axial), and postaxial polydactyly (ulnar). Mostly inherited as an autosomal dominant entity with variable penetrance and caused by defects that occur in the anterior-posterior patterning of limb development. In humans, to-date at least 10 loci and six genes causing non-syndromic polydactyly have been identified, including the ZNF141, GLI3, MIPOL1, IQCE, PITX1, and the GLI1. In the present review, clinical, genetic and molecular characterization of the polydactyly types has been presented including the recent genes and loci identified for non-syndromic polydactyly. This review provides an overview of the complex genetic mechanism underlie polydactyly and might help in genetic counseling and quick molecular diagnosis.

Keywords: PAP; PPD; digit anomalies; extra digits/toes; limb defects; polydactyly.

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Figures

FIGURE 1
FIGURE 1
Cartoon diagrams of autopods showing preaxial, postaxial, and complex polydactylies. Red filled elements portray the affected/polydactylous digits. Yellow filled elements portray dysplastic/hypoplastic bones and shaded digits represent syndactyly. (A) Representing PPD1 including (I) bifid thumb, hallucal polydactyly and (II) duplication of thumb and hallux. (B) Representing PPD2 including (I) opposable triphalangeal thumb and (II) non-opposable triphalangeal thumb. (C) Representing PPD3 including (I,II) duplication of the second digit. (D) Representing PPD4 including (I) toe webbing (Cross-type I) and (II) finger/toe webbing (Cross type II). (E) Representing PAPA, having (I) well developed fifth digit and (II) more proximal branching of the (5th) fifth digit. (F) Representing PAPB, (I) Pedunculated postminimus and (II) bifid fifth toe-pedunculated postminimus. (G) Representing complex polydactylies (I) showing mirror image preaxial duplications. (II) Central polydactyly (mesoaxial) in hand and foot. (III) Haas type polydactyly with complete syndactyly. (IV) Palmer/dorsal polydactyly.
FIGURE 2
FIGURE 2
Cartoon diagrams of autopods showing postaxial polydactyly (PAP) types A (PAPA1-PAPA7 and PAPA type A-EVC). Red filled elements portray the affected/polydactylous digits, yellow filled elements portray dysplastic/hypoplastic bones and shaded digits represent syndactyly. (A) Representing PAPA1, having a well developed extra digit in both upper and lower limbs. (B) Representing PAPA2, having extra digit restricted to upper limbs. (C) PAPA3, showing well developed extra digits in both upper and lower limbs. (D) PAPA4, having a well developed extra digit, PAPB also reported (skin tag without bone). (E,F) PAPA5, 6: Well developed extra digits and toes. (G) Representing PAPA7, having extra digit restricted to only toes. (H) Representing PAP type A-EVC, having PAP type A and PAP type B in both upper and lower limbs.
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