The animated videos in NORD’s Rare Disease Video Library provide brief introductions to rare disease topics for patients, caregivers, students, professionals and the public. NORD collaborates with medical experts, patient organizations, videographers and Osmosis to develop the videos, which are made possible by individual donations, educational grants and corporate sponsorships. NORD is solely responsible for the content.
Primary mitochondrial myopathies (PMM) are a group of disorders that are associated with changes in genetic material (e.g. depletions, deletions, or mutations) found within the DNA of mitochondria (mtDNA) or with genes outside the mitochondria (nuclear DNA), affecting predominantly the skeletal muscle. Mitochondria, found by the hundreds within every cell of the body, regulate the production of cellular energy and carry the genetic blueprints for this process within their own unique DNA (mtDNA). These disorders often hamper the ability of affected cells to break down food and oxygen and produce energy. Mitochondria provide more than 90% of the energy used by the body’s tissues; mitochondrial disorders are characterized by a lack of sufficient energy for cells of the body to function properly. High-energy tissues like muscle, brain, or heart tissue are most likely to be affected by mitochondrial disorders. In most mitochondrial disorders, abnormally high numbers of defective mitochondria are present in the cells of the body. Mitochondrial diseases often affect more than one organ system of the body. Most mitochondrial diseases affect the muscles (myopathy). Sometimes, muscle disease is the only or predominant sign of a mitochondrial disorder, thus defined as PMM. There are no disease-modifying treatments for PMM; treatment is aimed to improving or resolving specific symptoms.
Primary mitochondrial myopathies (PMM) are genetically defined disorders leading to defects of oxidative phosphorylation (see Causes section below) affecting predominantly, but not exclusively, skeletal muscle. Thus, secondary involvement of mitochondria, frequently observed in other neuromuscular diseases (e.g. Duchenne muscular dystrophy) is not considered PMM. Moreover, individuals with muscle disease symptoms but with other systems are affected (i.e. brain, liver, kidney, etc.) are not considered affected by PMM, and they may fit into a more straightforward clinical syndrome like Kearns-Sayre syndrome, MELAS syndrome, etc. NORD has individual reports on many different forms of mitochondrial disease. (For more information, choose the specific disorder name as your search term in the Rare Disease Database.)