Linkage of nonspecific X‐linked mental retardation to Xq21.31

Abstract

Mental retardation unassociated with the Fragile X syndrome accounts for up to 60% of patients with X-linked mental retardation. In this investigation, we report on a family with mild non-specific X-linked mental retardation (MRX) without other apparent phenotypic abnormalities. Linkage analysis on 27 relatives using 18 polymorphic markers spanning the X-chromosome demonstrated close linkage to DXYS1 with a peak LOD score of 2.14 at a theta of 0. Numerous families with various types of MRX have now been studied by other investigators using molecular genetic techniques. In addition to the family described in this report, a number of these have demonstrated linkage to the DXYS1 locus. These data suggest that a gene for mental retardation may exist in the region of DXYS1. Alternatively, this area of the X-chromosome may harbor multiple different but closely linked genes which cause the various types of MRX.

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

“…The MRX50 gene is located at region Xp11.3-Xp11.21, in the pericentromeric part of the short arm of the chromosome, overlapping with a large number of other MRX gene regions: MRX1 [Suthers et al, 1988;Gedeon et al, 1996], MRX5 [Sammans et al, 1991], MRX7 [Jedele et al, 1992], MRX8 [Schwartz et al, 1992], MRX9 [Willems et al, 1993], MRX10, MRX11, MRX12, and MRX13 [Kerr et al, 1992], MRX14 Gedeon et al, 1996], MRX15 , MRX18 , MRX20 [Lazzarini et al, 1994], MRX22 [Passos-Bueno et al, 1993], MRX26 [Robledo et al, 1996], MRX31 , and MRX38 [Schutz et al, 1996]. Gedeon et al [1996] hypothesize that all these MRX localizations clustering on the pericentromeric part of the Xp arm could be accounted for by 2 gene locations, namely the MRX1 and the MRX10 locations.…”

X‐linked mental retardation exhibiting linkage to DXS255 and PGKP1: a new MRX family (MRX14) with localization in the pericentromeric region

“…A maximum LOD score with DXYSlX at Xq21.31 has been reported for seven other families with mental retardation. Two had non-specific mental retardation, MRX7 (Jedele et al 1992) and MRX13 ) and five had severe syndromal XLMR : MRXS3 (Sutherland et al 1988), MRXS4 (Miles & Carpenter 1991), Allan-Herndon syndrome (Schwartz et al 1990, Bialer et al 1992), Wieacker-Wolff syndrome (Wieacker et al 1987) and Carpenter syndrome (Carpenter et al 1988). For MRX8, a multipoint LOD score of 2.36 for 8=0.00 was obtained with DXS326 at…”

Letter to the editor: How many X-linked genes for non-specific mental retardation (MRX) are there?

“…Genes isolated from translocation breakpoints or within deletions and which are expressed in neural tissue represent candidates for those MRX families where the genes map across these regions. Another region characterised by deletions lies in Xq28 adjacent to FRAXE [Gedeon et al, 19951 and contains elements of the FMR2 gene which is associated with FRAXE MR [Gecz et al, 19961. The lack of distinctive clinical criteria within the MRX group of X-linked mental retardations means that currently the only approach to differentiating between them is through non-overlapping regional localisations of the associated gene [Kerr, 19911 This study" Hu et al, 1994bGedeon et al, 1991Hu et al, 1994bSamanns et al, 1991Kondo et al, 1991Jedele et al, 1992Schwartz et al, 1992Willems et al, 1993 This study'…”