Refined mapping of the CSNU3 gene to a 1.8-Mb region on chromosome 19q13.1 using historical recombinants in Libyan Jewish cystinuria patients.

Cystinuria is a genetic disease manifested by the development of kidney stones. In some patients, the disease is caused by mutations in the SLC3A1 gene located on chromosome 2p. In others, the disease is caused by a gene that maps to chromosome 19q, but has not yet been cloned. Cystinuria is very common among Jews of Libyan ancestry living in Israel. Previously we have shown that the disease-causing gene in Libyan Jews maps to an 8-cM interval on chromosome 19q between the markers D19S409 and D19S208. Several markers from chromosome 19q showed strong linkage disequilibrium, and a specific haplotype was found in more than half of the carrier chromosomes. In this study we have analyzed Libyan Jewish cystinuria families with eight markers from within the interval containing the gene. Seven of these markers showed significant linkage disequilibrium. A common haplotype was found in 16 of the 17 carrier chromosomes. Analysis of historical recombinants placed the gene in a 1.8-Mb interval between the markers D19S430 and D19S874. Two segments of the historical carrier chromosome used to calculate the mutation's age revealed that the disease-causing mutation was introduced into this population 7-16 generations ago.