The MYOT gene provides instructions for making a protein called myotilin. Myotilin is found in heart (cardiac) muscle and muscles used for movement (skeletal muscle). Within muscle fibers, myotilin proteins are found in structures called sarcomeres, which are necessary for muscles to tense (contract). Myotilin attaches (binds) to other proteins to help form sarcomeres. Myotilin is also involved in linking neighboring sarcomeres to each another to form myofibrils, the basic unit of muscle fibers. The connection of sarcomeres to each other and the formation of myofibrils are essential for maintaining muscle fiber strength during repeated cycles of contraction and relaxation.
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At least five mutations in the MYOT gene have been found to cause myofibrillar myopathy. Most of these mutations are located in an area of the gene known as exon 2. MYOT gene mutations that cause myofibrillar myopathy change single protein building blocks (amino acids) in myotilin. Mutated myotilin proteins cluster together with other muscle proteins in the sarcomere to form clumps (aggregates). The aggregates prevent these proteins from functioning normally. A dysfunctional myotilin protein cannot properly bind with other proteins, preventing the formation of sarcomeres and myofibrils. MYOT gene mutations that cause myofibrillar myopathy impair the function of muscle fibers, causing weakness and the other features of this condition.