Post-axial polydactyly refers to polydactyly where the additional digit is on the ulnar margin of the hand, or lateral to the 5th (little) toe.
Post-axial polydactyly is more common than preaxial polydactyly, with an estimated incidence of 1 in 3000 5.
Post-axial polydactyly can be associated with:
- trisomy 13
- Bardet-Biedl syndrome
- Meckel Gruber syndrome
- McKusick-Kaufman syndrome
- following oral-facial-digital syndromes (OFDS)
- certain skeletal dysplasias
- Smith Lemli Opitz syndrome
- certain short rib polydactyly syndromes: e.g types I and III
The majority of cases are idiopathic. Associations with mutations to the GLI3 gene on chromosome 7 as well as a second locus mapped to chromosome 13 have been implicated in post-axial polydactyly 5.
Post-axial polydactyly has been defined by Temtamy and McKusick as:
- type A: additional digit at the MCP joint (or more proximally at the CMC joint)
- type B: small nubbin of non-functioning tissue or additional soft tissue on a pedicle
Or, you can use a separate three-part classification system:
- type I: nubbin or floating digit
- type II: duplications at the MCPJ
- type III: duplication of the entire ray
- 1. Tore HG, Mckinney AM, Nagar VA et-al. Syndrome of megalencephaly, polydactyly, and polymicrogyria lacking frank hydrocephalus, with associated MR imaging findings. AJNR Am J Neuroradiol. 2009;30 (8): 1620-2. doi:10.3174/ajnr.A1566 - Pubmed citation
- 2. Bowerman RA. Anomalies of the fetal skeleton: sonographic findings. AJR Am J Roentgenol. 1995;164 (4): 973-9. AJR Am J Roentgenol (abstract) - Pubmed citation
- 3. Son SH, Kim YJ, Kim ES et-al. A case of McKusick-Kaufman syndrome. Korean J Pediatr. 2011;54 (5): 219-23. doi:10.3345/kjp.2011.54.5.219 - Free text at pubmed - Pubmed citation
- 4. Poretti A, Brehmer U, Scheer I et-al. Prenatal and neonatal MR imaging findings in oral-facial-digital syndrome type VI. AJNR Am J Neuroradiol. 2008;29 (6): 1090-1. doi:10.3174/ajnr.A1038 - Pubmed citation
- 5. Hongshan Zhao, Yong Tian, Guido Breedveld, Shangzhi Huang, Ying Zou, Jue Y, Jinghua Chai, Hui Li, Mingyue Li, Ben A Oostra, Wilson H Y Lo, Peter Heutink. Postaxial polydactyly type A/B (PAP-A/B) is linked to chromosome 19p13.1-13.2 in a chinese kindred. (2002) European Journal of Human Genetics. 10 (3): 162. doi:10.1038/sj.ejhg.5200790