Regional localization of two genes for nonspecific X-linked mental retardation to Xp22.3-p22.2 (MRX49) and Xp11.3-p11.21 (MRX50)

Two families with nonspecific X-linked mental retardation (XLMR) are presented. In the first family, MRX49, 5 male patients in 2 generations showed mild to moderate mental retardation. Two-point linkage analysis with 28 polymorphic markers, dispersed over the X-chromosome, yielded a maximal LOD score of 2.107 with markers DXS7107 and DXS8051 at theta = 0.0, localizing the MRX49 gene at Xp22.3-p22.2, between Xpter and marker DXS8022. Multipoint linkage analysis showed negative LOD values over all other regions of the chromosome. In the second family, MRX50, 4 males in 2 generations showed moderate mental retardation. Pairwise linkage analysis with 28 polymorphic markers yielded a LOD score of 2.056 with markers DXS8054, DXS1055, and DXS1204, all at theta = 0.0. Flanking markers were DXS8012 and DXS991, situating the MRX50 gene at Xp11.3-Xp11.21, in the pericentromeric part of the short arm of the X chromosome.