X-LINKED JUVENILE RETINOSCHISIS - LOCALIZATION BETWEEN (DXS1195, DXS418) AND AFM291WF5 ON A SINGLE YAC

We studied 17 pedigrees with 108 affected males with X-linked juvenile retinoschisis (RS; McKusick No. 31270) and have analyzed all of the k nown polymorphic markers in the RS region of Xp22.1-p22.2 between DXS9 87 and DXS41. By haplotype analyses we found 7 individuals who showed crossovers in this interval surrounding RS, We previously reported AFM 291wf5 as the centromeric boundary, and this remains unchanged in the present study, A new recombination was identified on the telomeric sid e at (DXS1195, DXS418). Our data support the locus order Xpter - (DXS9 87, DXS207, DXS1053, DXS43) - (DXS1195, DXS418)- (RS, DXS257 DXS999) - (AFM291wf5, DXS443) - DXS1052 - (DXS1226, DXS274, DXS41) - Xcen; loci grouped in parentheses could not be mutually ordered by our genetic d ata, Physical mapping has indicated a distance of at most 900-1,000 kb between (DXS1195, DXS418) and AFM291wf5. No recombination was observe d between RS and DXS257 which lies in our new interval of interest, bu t one critical individual was not informative with this marker. Our da ta now define the smallest RS inclusion interval. This interval is con tained on a single YAC from which we have identified expressed sequenc es as candidate genes for RS.