X-linked nonspecific mental retardation (MRX16) mapping to distal Xq28: Linkage study and neuropsychological data in a large family

A genetic linkage study was performed on a large four-generation family wit h variable nonspecific X-linked mental retardation (MRX16), speech abnormal ities, and retardation of all milestones, Significant linkage was found in the Xq28 region with loci DXS52, DXS15, BGN, and DXS1108 with maximum LOD s cores of 4.86, 4,01, 4,83, and 5,43, respectively, at theta = 0,00, Recombi nation was observed at the locus DXS1113, thus mapping the gene in an 8-Mb interval between this marker and the Xq telomere. Linkage intervals of thre e other MRX families overlap with this interval in Xq28 where the RABGDIA g ene, mutated in the MRX41 and MRX48 families, is also located, In MRX3, MRX 28, but also in MRX16, no alteration of RABGDIA has been found, thus sugges ting the existence of at least two MRX genes in distal Xq28, Am, J, Med. Ge net. 83: 411-418, 1999. (C) 1999 Wiley-Liss, Inc.