XLMR genes: Update 1998

Since the Seventh Fragile X and XLMR Mental Retardation (XLMR) Workshop in 1995, the genes for Coffin-Lowry, Mohr-Tranebjaerg, and Opitz G/BBB syndrom es have been cloned. Jensen syndrome has been found to be allelic to Mohr-T ranebjaerg, Twenty new XLMR syndromes and metabolic or neuromuscular disord ers have been reported. Twenty-four new localizations have been established , including five in previously reported conditions (FG, Carpenter, Arts, OP A2, and OFD1), The number of families with nonspecific XLMR that have been reported has continued to increase; 58 families or loci are now known, Eigh teen new families with nonspecific mental retardation (MRX) have been repor ted. Two of them, however, were subsequently found to have mutations in the RABGDIA gene, which codes for a GDP-dissociation inhibitor for RAB protein s. In total, 41 more entries have been added to the X chromosome map of XLM R, The total number of known syndromes and MRX families has increased to 17 8, Of the 120 known XLMR disorders, 53 have been mapped, and 22 have been c loned. Assuming that at least 10 loci are necessary to account for the 58 f amilies with MRX, the total number of XLMR loci counted so far would be 130 , Although it is likely that many of the disorders will eventually prove to be allelic, it is not possible at present to determine the precise number of loci for nonspecific XLMR. (C) 1999 Wiley-Liss, Inc.