Severe X-linked myotubular myopathy with unexpected inheritance from the grandfather and identification of necklace fibers in an asymptomatic male


X-linked recessive myotubular myopathy (XLMTM) usually affects boys and is associated with mutations in the myotubularin gene (MTM1). In this study we describe a family with a severely affected infant boy with a centronuclear myopathy due to unexpected grand paternal transmission of a novel mutation in MTM1 (c.646_648dupGTT; p.Val216dup). The mother of the affected boy was heterozygous carrier of the variant whereas the maternal grandmother was homozygous for the wild-type allele. The maternal grandfather, who was reported to be healthy, was identified with both the mutated MTM1 gene together with wild-type MTM1.


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