Mitochondrial myopathies are types of

myopathies In medicine, myopathy is a disease of the muscle in which the muscle fibers do not function properly. This results in muscular weakness. ''Myopathy'' means muscle disease (Greek : myo- ''muscle'' + patheia '' -pathy'' : ''suffering''). This mean ...

associated with

mitochondrial disease Mitochondrial disease is a group of disorders caused by mitochondrial dysfunction. Mitochondria are the organelles that generate energy for the cell and are found in every cell of the human body except red blood cells. They convert the energy of ...

. On biopsy, the muscle tissue of patients with these diseases usually demonstrate "ragged red" muscle fibers. These ragged-red fibers contain mild accumulations of glycogen and neutral lipids, and may show an increased reactivity for

succinate dehydrogenase Succinate dehydrogenase (SDH) or succinate-coenzyme Q reductase (SQR) or respiratory complex II is an enzyme complex, found in many bacterial cells and in the inner mitochondrial membrane of eukaryotes. It is the only enzyme that participates i ...

and a decreased reactivity for

cytochrome c oxidase The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory electr ...

. Inheritance was believed to be maternal ( non-Mendelian extranuclear). It is now known that certain nuclear DNA deletions can also cause mitochondrial myopathy such as the OPA1 gene deletion. There are several subcategories of mitochondrial myopathies.

Signs and symptoms

Signs and symptoms include (for each of the following causes): * Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like syndrome (MELAS) ** Varying degrees of cognitive impairment and dementia **

Lactic acidosis Lactic acidosis is a medical condition characterized by a build-up of lactate (especially -lactate) in the body, with formation of an excessively low pH in the bloodstream. It is a form of metabolic acidosis, in which excessive acid accumulates ...

Stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

s **

Transient ischemic attack A transient ischemic attack (TIA), commonly known as a mini-stroke, is a minor stroke whose noticeable symptoms usually end in less than an hour. TIA causes the same Symptoms of stroke, symptoms associated with strokes, such as weakness or numbn ...

s ** Hearing loss ** Weight loss * Myoclonic epilepsy and ragged-red fibers (MERRF) ** Progressive myoclonic epilepsy ** Clumps of diseased mitochondria accumulate in muscle fibers and appear as "ragged-red fibers" when muscle is stained with modified

Gömöri trichrome stain Gömöri trichrome stain is a histological stain used on muscle tissue. It can be used to test for certain forms of mitochondrial myopathy. It is named for George Gömöri George Gomori may refer to: * György Gömöri (1904–1957), Hungari ...

** Short stature *

Kearns–Sayre syndrome Kearns–Sayre syndrome (KSS), oculocraniosomatic disorder or oculocranionsomatic neuromuscular disorder with ragged red fibers is a mitochondrial myopathy with a typical onset before 20 years of age. KSS is a more severe syndromic variant of chron ...

(KSS) ** External

ophthalmoplegia Ophthalmoparesis refers to weakness (-paresis) or paralysis (-plegia) of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic, ophthalmologic, and endocrine disease. Internal o ...

** Cardiac conduction defects **

Sensorineural hearing loss Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). SNHL accounts for about 90% of rep ...

Chronic progressive external ophthalmoplegia Chronic progressive external ophthalmoplegia (CPEO) is a type of eye disorder characterized by slowly progressive inability to move the eyes and eyebrows. It is often the only feature of mitochondrial disease, in which case the term CPEO may be g ...

(CPEO) ** Progressive

ophthalmoparesis Ophthalmoparesis refers to weakness (-paresis) or paralysis (-plegia) of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic, ophthalmologic, and endocrine disease. Internal o ...

** Symptomatic overlap with other mitochondrial myopathies

Cause

Mitochondrial myopathy literally means mitochondrial muscle weakness, muscle weakness caused by mitochondrial dysfunction. The mitochondrion is the powerhouse of the cell. Every muscle cell has mitochondria, and if the muscle cell’s mitochondria have problems by which there is not enough energy to function or perform its duties, problems occur. The cause may be genetic, such as a variation within the POLG (polymerase gamma) gene, which causes mitochondrial DNA (mtDNA) to become damaged and lose function.

Diagnosis

Muscle biopsy: ragged red fibers in

Treatment

Although no cure currently exists, there is hope in treatment for this class of

hereditary disease A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...

s with the use of an embryonic mitochondrial transplant.

References

External links