What causes myosin storage myopathy (hyaline body myopathy)?

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

Mutations in the slow/β-cardiac myosin heavy-chain gene (MYH7) have been reported in sporadic or autosomal dominantly inherited cases. Mutations in MYH7 also cause Laing early adult-onset distal myopathy type 3 and cases of familial hypertrophic cardiomyopathy, dilated cardiomyopathy and left ventricular non-compaction. The same mutation may present with variable phenotypes as exemplified by one mutation (Leu1793Pro) shown to present with neonatal hypotonia, adult-onset proximal weakness and isolated neonatal cardiomyopathy. [63]  Mutations in MYH7 also cause hypertrophic cardiomyopathy (CMH-1), dilated cardiomyopathy (CMD-1S), and familial left ventricular noncompaction.

Hyaline bodies are subsarcolemmal areas, mostly in type-1 muscle fibers, that are devoid of sarcomeres and react with myosin ATPase but not oxidative enzymes or glycogen. They are pink on hematoxylin and eosin (H&E) staining, and pale green with modified GT staining. They are composed of granular and filamentous material in continuity with adjacent thick myosin filaments. The hyaline bodies immunostain intensely with antibodies against the slow myosin heavy chain and have been proposed to result from myofibrillolysis of the mutated slow myosin heavy chain within type-1 muscle fibers.

Type-1 muscle fiber predominance is common. 

Interestingly, some patients with a mutation in MYH7 do not have hyaline bodies on muscle biopsy sample.

Onset is usually in infancy or childhood but with variable penetrance; some patients present in adult life or may even be asymptomatic in their 40s. [64]  Their weakness can be proximal, proximal and distal, or scapuloperoneal in distribution. Progression is minimal or very slow; more rapid progression is rare.


Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!