What causes spheroid body myopathy?

Updated: Mar 11, 2019
  • Author: Matthew Harmelink, MD; Chief Editor: Amy Kao, MD  more...
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Answer

This myopathy is due to an autosomal dominant mutation in the gene for myotilin (titin immunoglobulin domain protein; TTID), which also causes LGMD type 1A and a myofibrillar myopathy. This has been described in one large kindred. [73]  

Spheroid bodies are more common in type-1 muscle fibers and devoid of enzymatic activity. Electron microscopy shows fine filaments and streaming of Z disks. Immunohistochemical studies show the presence of desmin and ubiquitin, similar to what is found in many myofibrillar myopathies.

Myotilin binds actin and is thought to be involved in stabilization of actin bundles and anchorage of thin filaments at the Z disk.

This myopathy can be considered a myofibrillar myopathy/desminopathy since aggregates include desmin. Mutations in myotilin also cause LGMD type 1A (Limb-Girdle Muscular Dystrophy.

Presentation varied from childhood to the eighth decade, most often with proximal weakness that slowly progressed, as well as dysarthric speech.

Swallowing difficulties, loss of ambulation, and need for respiratory support occurred in a few individuals.


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