X-linked recessive myotubular myopathy (XLMTM) is a very severe congenital 
muscular disease characterised by an impaired maturation of muscle fibres, and 
caused by defects in the MTM1 gene. This gene defines a new family of putative 
tyrosine phosphatases conserved through evolution. We have determined intronic 
flanking sequences for all the 15 exons to facilitate the detection of mutations 
in patients and genetic counselling. We characterised a new polymorphic marker 
in the immediate vicinity of the gene, which might prove useful for linkage 
analysis. Sequencing of the TATA-less predicted promoter provides the basis for 
transcriptional regulatory studies.