LINKAGE MAPPING OF A LARGE COLOMBIAN FAMILY SEGREGATING FOR X-LINKED RETINOSCHISIS - REFINEMENT OF THE CHROMOSOMAL LOCATION

Juvenile X linked retinoschisis (RS) is a bilateral vitreoretinal dyst rophy that develops early in life. Previous linkage studies have local ised the RS gene to Xp22.1-p22.3 between DXS207 and AFM 291Wf5, which represents a genetic distance of approximately 3.7 cM. In an effort to facilitate the eventual cloning of the RS gene, we have analysed a la rge Colombian family, using 10 microsatellite markers that have been m apped to the region Xp22.1-p22.3. A total of 93 members, including 19 affected and eight unaffected males, two affected females, and six obl igate carrier females were analysed. Close linkage was observed betwee n the disease locus and DXS999 (Zmax=2.27, theta max=0.05), DXS987 (Zm ax=2.61, theta max=0.1), DXS443 (Zmax=4.23, theta max=0.1), and DXS274 (Zmax=3.49, theta max=0.05) markers. Recombination with the RS locus was found for all marker loci except DXS197, DXS43, and DXS1195. These results place the RS locus within an interval of approximately 2 cM b etween the flanking markers DXS1053 and DXS999, approximately 1.7 cM c loser than the previously reported boundary. The results also further confirm the lack of genetic heterogeneity of RS.