Confirmation of genetic homogeneity of syndactyly type IV and triphalangeal thumb-polysyndactyly syndrome in a Chinese family and review of the literature

Syndactyly type IV (SD4) is inherited in an autosomal dominant fashion and characterized by complete cutaneous syndactyly of all fingers accompanied with polydactyly. Triphalangeal thumb-polysyndactyly syndrome (TPTPS) consists of a triphalangeal thumb, polydactyly, and syndactyly and is transmitted in an autosomal dominant manner with variable expression. Genomic duplications of the long-range limb-specific cis-regulator (ZRS) cause SD4 and TPTPS. Here, we report two individuals from a Chinese family with syndactyly. One individual had overlapping clinical symptoms of TPTPS and SD4, while the other had a typical SD4 with postaxial polydactyly of the toe. Results of quantitative PCR suggested that the duplication of ZRS involved all affected individuals, and array comparative genomic hybridization detected its size as 115.3 kb. Conclusion: This work confirms the genetic homogeneity of SD4 and TPTPS. Our result expands the spectrum of ZRS duplications. TPTPS and SD4 should be considered as a continuum of phenotypes.