X-linked myotubular myopathy: Living longer and awaiting treatment.

Abstract

The congenital myopathies (CMs) are a cluster of genetic disorders affecting myofiber structure and function. The salient clinical features are hypotonia, weakness, and motor impairment. The presentation varies from the most severe impairment in the newborn to a range of phenotypes in infancy (“floppy baby”), childhood, or occasionally adulthood. The prevalence of CMs is ≈1:26,000 children (birth to 17 years).1 The CMs were named on the basis of distinctive morphologic abnormalities seen on muscle biopsy: nemaline myopathy, with rods due to protein accumulation; core myopathy, with cores or multiminicores devoid of oxidative enzyme activity; centronuclear myopathy, with abnormal centrally placed nuclei; and congenital fiber-type disproportion, with a predominance of small type 1 fibers. Specific clinical features, e.g., ophthalmoparesis and facial, bulbar, and respiratory weakness, and muscle MRI can point toward a specific diagnosis.2 Standard-of-care guidelines for the CMs were published in 2012.3