Summary
Postaxial polydactyly is defined as the presence of an extra digit near the fifth digit and/or toe. This anomaly is present in one newborn in 2 000 in Europe. It is ten times more frequent in Africa. It can be strictly isolated or part of a multiple malformation syndrome, which might be linked to the mutation of one or several identified genes (90 syndromes identified so far) or to chromosomal abnormalities (deletion, inversion, duplication, translocation, etc). The isolated form can consist of type A polydactyly, where the digit is completely formed, or type B, where the extra digit presents as a skin tag. Postaxial polydactyly is generally transmitted as an autosomal dominant trait with variable penetrance and expressivity. One gene and three loci have been identified to date: GLI3 (located in 7p13.6), PAPA2 (postaxial polydactyly type A2, 13q21-q32), PAPA3 (19p13.1-13.2) and PAPA4 (7q21-7q34). The PAPA2 locus is associated with type A polydactyly, whereas both types A and B can be observed in families with mutations of the GLI3 gene or linked to PAPA3 and PAPA4 loci. Management is surgical, with cosmetic aim. *Author: Prof. D. Lacombe (August 2007)*.
