Fine mapping of progressive pseudorheumatoid dysplasia: a tool for heterozygote identification.

Progressive pseudorheumatoid dysplasia is a skeletal genetic disorder affecting primarily the articular cartilage, causing joint stiffness and leading to a crippling status. More than two-thirds of the reported patients belong to Arab and Mediterranean populations. The disease locus has been mapped to chromosome 6q22 in a region of 12.9 cM using a Jordanian family. We examined two additional families, one Jordanian and one Palestinian, to test for homogeneity of the disorder and the presence of a common haplotype, to fine map the disorder, and to use all the information to derive a tool for heterozygote identification. The two families showed linkage to the same previously reported locus, thus suggesting homogeneity, but they did not share a common haplotype. They also provided information that refined the genetic region for the disease locus to 2.1 cM with three microsatellite markers. The absence of a common haplotype indicates that no common ancestor mutations were inherited by our patients. Genotyping for the three-marker haplotype showed that it can be used as a heterozygote identification tool.