Mental Retardation, X-Linked 20

Description

Impaired mental functioning occurs as an isolated feature or as part of many syndromes listed in the X-linked catalog. Mental retardation that is not associated with other distinguishing features is referred to as 'nonspecific.'

The Human Gene Mapping Nomenclature Committee (Mulley et al., 1992) proposed to designate each newly reported apparently unique X-linked mental retardation (MRX) family with gene symbols (e.g., MRX1, MRX2) if a minimal lod score of 2.0 was demonstrated between the MR locus and 1 or more X chromosome markers.

Mapping

Lazzarini et al. (1995) reported a family with MRX20. Fragile X syndrome was excluded cytogenetically and by absence of linkage to the Xq27.3 region. On the other hand, linkage studies using short tandem repeat polymorphism (STRP) markers indicated that the mutation is at a locus in the centromeric region of the X chromosome.