Mapping of a gene for non-specific X linked mental retardation: evidence for linkage to chromosomal region Xp21.1-Xp22.3.

Linkage analysis of a non-specific form of X linked mental retardation (MRX) was performed with 16 polymorphic markers spanning the entire X chromosome in a three generation Italian family, including four male patients with moderate mental retardation. One obligate carrier woman had mild mental retardation and another two had normal intelligence. The results indicate tight linkage to DNA markers DXS84 (L754), DXS164 (pERT87-15), and DXS278 (CRI-S232). A maximum lod score of 2.11 at theta = 0.00 was obtained with DXS164 and DXS278. The linked region spanned chromosomal bands Xp21.1-Xp22.3, that is, the same portion of the X chromosome where MRX2 and MRX10-13 have been previously localised.