Polyalanine repeat expansion mutation of the HOXD13 gene in a Chinese family with unusual clinical manifestations of synpolydactyly

Synpolydactyly (SPD) is an autosomal dominant limb malformation caused by mutations in the gene HOXD13. We investigated a Chinese family in which three individuals across three generations were affected with distinctive limb malformations. We extracted genomic DNA from the affected and three unaffected individuals from this family as well as 100 unrelated controls, for mutation detection by DNA sequencing. The family was characterized by camptodactyly and symphalangism of fingers two to five, transverse phalanx and osseous fusion of the third metacarpal with the proximal phalanx, as well as the coexistence of mild and more severe bilateral phenotypes. We identified a duplication mutation, c. 186–212dup, in exon 1 of the HOXD13 gene in the affected individuals from this family; it was not present in the unaffected individuals or the 100 unrelated individuals. And we also did not find polymorphism among the controls. This study has expanded the phenotypic spectrum of known HOXD13 polyalanine repeat mutations and provided more information about the polymorphic nature of the polyalanine repeat. In addition, new clinical manifestations have been added to the spectrum of possible synpolydactyly phenotypes.