X-linked myotubular myopathy

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X-linked myotubular myopathy
Classification and external resources
OMIM 310400

X-linked myotubular myopathy (MTM) is a form of centronuclear myopathy (CNM) associated with myotubularin 1.

Genetically inherited traits and conditions are often referred to based upon whether they are located on the "sex chromosomes" (the X or Y chromosomes) versus whether they are located on "autosomal" chromosomes (chromosomes other than the X or Y). Thus, genetically inherited conditions are categorized as being sex-linked (e.g., X-linked) or autosomal. Females have two X-chromosomes, while males only have a single X chromosome, and a genetic abnormality located on the X chromosome is much more likely to cause clinical disease in a male (who lacks the possibility of having the normal gene present on any other chromosome) than in a female (who is able to compensate for the one abnormal X chromosome).

The X-linked form of MTM is the most commonly diagnosed type. Almost all cases of X-linked MTM occurs in males. Females can be "carriers" for an X-linked genetic abnormality, but usually they will not be clinically affected themselves. Two exceptions for a female with a X-linked recessive abnormality to have clinical symptoms: one is a manifesting carrier and the other is X-inactivation. A manifesting carrier usually has no noticeable problems at birth; symptoms show up later in life. In X-inactivation, the female (who would otherwise be a carrier, without any symptoms), actually presents with full-blown X-linked MTM. Thus, she congenitally presents (is born with) MTM.[1] Thus, although MTM1 mutations most commonly cause problems in boys, these mutations can also can clinical myopathy in girls, for the reasons noted above. Girls with myopathy and a muscle biopsy showing a centronuclear pattern should be tested for MTM1 mutations.[1]

Many clinicians and researchers use the abbreviations XL-MTM, XLMTM or X-MTM to emphasize that the genetic abnormality for myotubular myopathy (MTM) is X-linked (XL), having been identified as occurring on the X chromosome. The specific gene on the X chromosome is referred to as MTM-1. In theory, some cases of CNM may be caused by an abnormality on the X chromosome, but located at a different site from the gene MTM1, but currently MTM1 is the only X-linked genetic mutation site identified for myotubular or centronuclear myopathy. Clinical suspicion for X-linked inheritance would be a disease affecting multiple boys (but no girls) and a pedigree chart showing inheritance only through the maternal (mother’s) side of each generation.


  1. ^ a b Jungbluth H, Sewry C, Buj-Bello A, Kristiansen M, Ørstavik K, Kelsey A, Manzur A, Mercuri E, Wallgren-Pettersson C, Muntoni F (2003). "Early and severe presentation of X-linked myotubular myopathy in a girl with skewed X-inactivation". Neuromuscul Disord. 13 (1): 55–9. doi:10.1016/S0960-8966(02)00194-3. PMID 12467733. 

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