Miyoshi What????

Miyoshi Myopathy is a rare form of muscular dystrophy which is part of the limb-girdle group of muscular dystrophy. Miyoshi is caused by defects in the gene for the protein dysferlin. It is categorized as a distal muscular dystrophy, which means that the muscles that are most strongly affected initially are in the calves, forearms, hands, or feet. Most other forms of muscular dystrophy primarily begin in proximal muscles (those in the hips, thighs, or shoulders), so those that don't follow that pattern were grouped together for classification purposes. There are many forms of distal myopathy but Miyoshi Myopathy is different from the other distal myopathies in several respects:

 

• It is recessive. This means that in most cases there is no family history.
• The first muscles to be affected are typically the gastrocnemius (the calf muscles in the back of the legs used to stand on tiptoe).
• Onset of symptoms generally occurs between the ages of 15 and 30. There are exceptions to this age range: genetically confirmed cases have been reported in the literature with onset as late as age 73.
• Levels of CK (creatine kinase, a muscle enzyme) in the blood are very high. Values typically found in Miyoshi patients are several thousand, compared to a normal reading of 100 or less. This is typical of some other muscular dystrophies but not most of the distal forms.
• Muscle biopsies show indications of a muscle disease, including degeneration/regeneration of muscle fibers, and often show evidence of inflammation.
• There are typically no symptoms of neuropathy, and tests of nerve conduction generally yield normal results.

There are three genetically identified types of Miyoshi Myopathy - MMD1, MMD2, MMD3.  MMD1 is the type that is caused by mutations in the dysferlin gene.  MMD3 is the type that is caused by mutations in Anoctamin 5. The gene for MMD2 has not yet been identified, but it is known that MMD2 is distinct from MMD1 or MMD3.  These types of Miyoshi Myopathy are indistinguishable clinically and can only be differentiated by the identification of mutations in the particular genes.

 

-The information above was obtained from the Jain Foundation website. For this and more information on Miyoshi Myopathy visit www.jain-foundation.org.