Isolated postaxial polydactyly type B with mosaicism of a submicroscopic unbalanced translocation leading to an extended phenotype in offspring.

Postaxial polydactyly (PAP) is characterized by the presence of one or more extra ulnar or fibular digits or parts of it. PAP type B presents frequently as a skin tag on the hand(s). It is usually an isolated malformation, but in 6.6% it is associated with other congenital abnormalities, mostly well recognizable syndromes. We present a male with PAP-B only and his daughter with an extended phenotype including mental retardation and minor dysmorphisms. Both share a cytogenetically balanced t(4;7)(p15.2;q35), present in mosaicism in the father. We found microdeletions associated with the breakpoints. The chromosomal regions described here have not been previously associated with the PAP-B phenotype. We present the first case of an individual with isolated PAP-B and a submicroscopic chromosome abnormality.