IMPROVED GENETIC-MAPPING OF X-LINKED RETINOSCHISIS

X linked retinoschisis (RS) causes poor vision in affected males owing to radial cystic changes at the macula. Genetic linkage analysis was carried out in 16 British families with X linked retinoschisis using m arkers from the Xp22 region. Linkage was confirmed between the RS locu s and the markers DXS207 (led score, Zmax = 17.9 at recombination frac tion theta = 0.03; confidence interval for theta = 0.007-0.09), DXS105 3 (Zmax = 18.0 at theta = 0.01, CI = 0.001-0.06), DXS43 (Zmax = 12.9 a t theta = 0.03, CI = 0.004-0.09), DXS1195 (Zmax = 6.4 at theta = 0.00) , DXS418 (Zmax = 8.2 at theta = 0.00), DXS999 (Zmax = 21.2 at theta = 0.01, CI = 0.001-0.05), DXS443 (Zmax = 14.2 at theta = 0.03, CI = 0.00 4-0.09), DXS365 (Zmax = 24.5 at theta = 0.008, CI = 0.001-0.04). Key r ecombinants placed RS between DXS43 distally and DXS999 proximally. Mu ltipoint linkage analysis gave odds of 344:1 in favour of this locatio n for RS and supported the map Xpter-(DXS207, DXS1053)-DXS43-1 cM-RS-1 cM-DXS999-DXS443-DXS365-DXS1052-Xcen.