Localization of a non-specific X-linked mental retardation gene, MRX23, to Xq23-q24

More than 100 X-linked mental retardation syndromes have been described. We report the localization of the disease gene, MRX23, in one family to Xq23-24. Affected family members present with non- specific X-linked mental retardation with verbal disability (BDOAS 10, 1-100). MRX23 is tightly linked to the markers DXS1220 (Z = 3.76 at theta = 0.1) and DXS424 (Z = 3.9 at theta = 0.06). Multipoint linkage analysis, taking five loci (DXS1072-0.07-DXS1220-0.014-MRX23-0.01-DXS 424-0.08-DXS1001) at a time, gives a maximum LOD score of 6.7 between these two markers. The next most likely location, between DXS424 and DXS1001 is 120-fold less likely. Haplotype analysis also indicates the most likely location for the disease gene is between DXS1220 and DXS424.