LOCALIZATION OF A NEW GENE FOR NONSPECIFIC MENTAL-RETARDATION TO XQ22-Q26 (MRX35)

Non-specific mental retardation (MR) is a condition in which MR appear s to be the only consistent manifestation. The X linked form (MRX) is genetically heterogeneous. We report clinical, cytogenetic, and Linkag e data on a family with X linked non-specific MR. Two point and multip oint Linkage analysis with 18 polymorphic markers, covering the entire chromosome, showed close Linkage to DXS1001 and DXS425 with a maximal lod score of 2.41 at 0% recombination. DXS178 and the gene for hypoxa nthine phosphoribosyltransferase (HPRT), located in Xq22 and Xq26 resp ectively, flank the mutation. All other chromosomal regions could be e xcluded with odds of at least 100:1. To our knowledge there is current ly no other nonspecific MR gene mapped to this region. Therefore, the gene causing MR in this family can be considered to be a new, independ ent MRX locus (MRX35).