Mental Retardation, X-Linked 50

Clinical Features

Claes et al. (1997) added 2 families to the growing list of nonspecific X-linked mental retardation (XLMR) families in which the disease gene could be mapped to a specific site on the X chromosome. The first family reported was designated MRX49 (300114). The second of these families, designated MRX50, contained 4 males in 2 generations showing moderate mental retardation.

Mapping

Linkage analysis in the MRX50 family by Claes et al. (1997) showed location of the locus at Xp11.3-p11.21 in the pericentromeric part of the short arm of the X chromosome, overlapping with a large number of other MRX gene regions: MRX1 (309530), MRX5, MRX7, MRX8, MRX9 (309549), MRX10, MRX11, MRX12 (300957), MRX13, MRX14 (300062), MRX15, MRX18, MRX22, MRX26, MRX31, and MRX38 (see 300419). Gedeon et al. (1996) hypothesized that all of the MRX assignments clustered on the pericentromeric part of Xp could be accounted for by 2 gene locations, namely the MRX1 and the MRX10 locations. Some of these families with pericentromeric gene locations show additional characteristic abnormalities and some of them show manifestations of disease in heterozygous carriers. Claes et al. (1997) commented that whether these clinical differences reflect allelic variability or locus heterogeneity will become clear only after the cloning of the responsible genes.