Here we report on the localization of a presumptive MRX gene to chromosomal region Xq24-q26 in a German family with nonspecific X-linked mental retardation (MRX 75, HUGO Human Gene Nomenclature Committee).
Thorough investigation of an MRX critical region in Xp22.1-21.3 enabled us to identify a new gene expressed in brain that is responsible for a non-specific form of X-linked mental retardation.
Most considerably, genotype-phenotype correlation studies of affected individuals in XLMR families with MRX gene mutations are necessary to define the criteria of MRX vs MRXS subclassification.