What are the genetic changes related to Miyoshi myopathy ?
Miyoshi myopathy is caused by mutations in the DYSF or ANO5 gene. When this condition is caused by ANO5 gene mutations it is sometimes referred to as distal anoctaminopathy. The DYSF and ANO5 genes provide instructions for making proteins primarily found in muscles that are used for movement (skeletal muscles). The protein produced from the DYSF gene, called dysferlin, is found in the thin membrane called the sarcolemma that surrounds muscle fibers. Dysferlin is thought to aid in repairing the sarcolemma when it becomes damaged or torn due to muscle strain.  The ANO5 gene provides instructions for making a protein called anoctamin-5. This protein is located within the membrane of a cell structure called the endoplasmic reticulum, which is involved in protein production, processing, and transport. Anoctamin-5 is thought to act as a channel, allowing charged chlorine atoms (chloride ions) to flow in and out of the endoplasmic reticulum. The regulation of chloride flow within muscle cells plays a role in controlling muscle tensing (contraction) and relaxation.  DYSF or ANO5 gene mutations often result in a decrease or elimination of the corresponding protein. A lack of dysferlin leads to a reduced ability to repair damage done to the sarcolemma of muscle fibers. As a result, damage accumulates and leads to atrophy of the muscle fiber. It is unclear why this damage leads to the specific pattern of weakness and atrophy that is characteristic of Miyoshi myopathy. The effects of the loss of anoctamin-5 are also unclear. While chloride is necessary for normal muscle function, it is unknown how a lack of this chloride channel causes the signs and symptoms of Miyoshi myopathy.