4 weeks
CPT Code 
Test Code 
Test Methods 
Specimen Types Accepted 
Cultured Cells
Extracted DNA

Centronuclear myopathy (CNM) is a rare muscle disease associated with non-progressive or slowly progressive muscle weakness that can develop from infancy to adulthood. On muscle histopathology, patients with CNM have increased frequency of central nuclei, as well as type 1 fiber predominance and hypotrophy, in the absence of other significant abnormalities. Patients with X-linked myotubular myopathy (XLMTM) [OMIM#310400] generally present with hypotonia, feeding difficulties, respiratory distress, and delayed motor milestones. Death in infancy is common in males with the classic form of this condition. Intelligence is usually normal. Muscle of patients with XLMTM appears similar to fetal myotubes, with small rounded muscle fibers and no surrounding contractile elements. Female carriers generally do not have significant muscle weakness or notable features of XLMTM, although there have been several cases of symptomatic carriers with skewed X-inactivation. XLMTM is caused by mutations in the MTM1 [OMIM#300415] gene located at Xq28. Approximately 80% of males with a diagnosis of myotubular myopathy by muscle biopsy will have a mutation in MTM1 identifiable by sequence analysis. About 7% of mutations in MTM1 are deletions.