Phenotypic variability of triphalangeal thumb-polysyndactyly syndrome linked to chromosome 7q36

Triphalangeal thumb-polysyndactyly (TPT-PS) is an isolated limb malformatio n consisting of pre- and postaxial polysyndactyly of hands and feet. The on ly family reported so far is of Dutch origin, and the genetic mapping study localized the TPT-PS locus at chromosome region 7q36 where the isolated tr iphalangeal thumb (TPT) anomaly has also been mapped. It was suggested that TPT-PS is a phenotypic variation of isolated TPT, and the same ancestral m utation may produce both phenotypes, Here we report on the second family wi th this malformation from the Turkish population. The characteristic findin gs in this family are triphalangeal thumb, webbing between 3rd, 4th, and 5t h fingers associated with bony synostosis in the distal phalanges of the sa me fingers, and pre- and postaxial polysyndactyly of feet. Some individuals show a more severe phenotype with a complete syndactyly of all fingers giv ing a "cup-like" appearance to the hands. Genetic linkage study with DNA ma rkers D7S1823, D7S550, D7S559, and D7S2423 demonstrated that this family is also linked to chromosome band 7q36. Identification of a second family fro m a distinct ethnic background suggests that TPT-PS and isolated TPT are no t caused by the same ancestral mutation as it was originally anticipated, A m. J. Med. Genet. 87:399-406, 1999. (C) 1999 Wiley-Liss, Inc.