XLMR in MRX families 29, 32, 33 and 38 results from the dup24 mutation in the ARX (Aristaless related homeobox) gene

Background X-linked mental retardation (XLMR) is the leading cause of mental retardation in males. Mutations in the ARX gene in Xp22.1 have been found in numerous families with both nonsyndromic and syndromic XLMR. The most frequent mutation in this gene is a 24 bp duplication in exon 2. Based on this fact, a panel of XLMR families linked to Xp22 was tested for this particular ARX mutation.