Genomic Organization of a 225-kb Region in Xq28 Containing the Gene for X-Linked Myotubular Myopathy (MTM1) and a Related Gene (MTMR1)

MTM1is responsible for X-linked recessive myotubular myopathy, which is a congenital muscle disorder linked to Xq28.MTM1is highly conserved from yeast to humans. A number of related genes also exist. TheMTM1gene family contains a consensus sequence consisting of the active enzyme site of protein tyrosine phosphatases (PTPs), suggesting that they belong to a new family of PTPs. Database searches revealed homology of myotubularin and all related peptides to the cisplatin resistance-associated α protein, which implicates an as yet unknown function. In addition, homology to the Sbf1 protein (SET binding factor 1), involved in the oncogenic transformation of fibroblasts and differentiation of myoblasts, was also evident. We describe 225 kb of genomic sequence containingMTM1and the related gene,MTMR1,which lies 20 kb distal toMTM1.Although there is only moderate conservation of the exons, the striking similarity in the gene structures indicates that these two genes arose by duplication. Calculations suggest that this event occurred early in evolution long before separation of the human and mouse lineages. So far, mutations have been identified in the coding sequence of only 65% of the patients analyzed, indicating that the remaining mutations may lie in noncoding regions ofMTM1or possibly inMTMR1.Knowledge of the genomic sequence will facilitate mutation analyses of the coding and noncoding sequences ofMTM1andMTMR1.