GENETIC-ANALYSIS OF NEW FRENCH X-LINKED JUVENILE RETINOSCHISIS KINDREDS USING MICROSATELLITE MARKERS CLOSELY LINKED TO THE RS LOCUS - FURTHER NARROWING OF THE RS CANDIDATE REGION

The gene involved in juvenile retinoschisis (RS) has previously been l ocalized, by genetic linkage analyses, to Xp22.1-p22.2, between DXS274 and DXS43/DXS207; it is closely linked to the latter markers. From ou r recent data, this interval represents a genetic distance of approxim ately 10 cM. In the present study, we have studied 14 French families with X-linked juvenile RS by using four CA polymorphisms that are clos ely linked to the RS locus and that have recently been included in an Xp22.1-p22.2 high-resolution map. Complete cosegregation with the dise ase locus was observed for three of them, DXS207, DXS418, and DXS999, which further confirms the locus homogeneity for RS and the close link age to this region. One recombinant was found with the most proximal m arker, AFM291 wf5, thereby defining this marker as the new proximal bo undary of the candidate region for RS. Under the assumption that DXS20 7 and DXS43 constitute the distal boundary, the present study further reduces the region containing the disease gene to a interval of 3-4 cM . The results reported here should facilitate the eventual cloning of the RS gene.