Mitochondrial myopathies are types of myopathies associated with mitochondrial disease. 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 and a decreased reactivity for cytochrome c oxidase. 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
Strokes
Transient ischemic attacks
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
Short stature
Kearns–Sayre syndrome (KSS)
External ophthalmoplegia
Cardiac conduction defects
Sensorineural hearing loss
Chronic progressive external ophthalmoplegia (CPEO)
Progressive ophthalmoparesis
Symptomatic overlap with other mitochondrial myopathies

Cause
Zidovudine, an HIV medication can cause red ragged fiber myopathy. Diagnosis
Muscle biopsy: ragged red fibers in Gömöri trichrome stain. Treatment
Although no cure currently exists, there is hope in treatment for this class of hereditary diseases with the use of an embryonic mitochondrial transplant. References


== External links ==
It then acts as an endonuclease to incise the damaged DNA strand on the 5 side of the damaged site. Mutant cells with deficient ERCC1-XPF are not only defective in NER, but also in the repair of double-strand breaks and inter-strand crosslinks. The XPG protein is an endonuclease that incises DNA during NER at the 3 side of the damaged nucleotide. Mutations in the XPG (ERCC5) gene can lead to XP alone, or in combination with Cockayne syndrome (CS), or in combination with infantile lethal cerebro-oculo-facio-skeletal syndrome. Diagnosis
Types
There are seven complementation groups, plus one variant form:

Treatment
There is no cure for the disorder; all treatment is symptomatic or preventive. Symptoms can be avoided or controlled by completely avoiding exposure to sunlight, either by staying indoors or wearing protective clothing and using sunscreen when outdoors. Keratosis can also be treated by using cryotherapy or fluorouracil. In more severe cases of XP, even minuscule amounts of UV light, for example, from covered windows or fluorescent bulbs, can be very dangerous and trigger symptoms.On September 10, 2020, Clinuvel Pharmaceuticals announced that it was investigating the use of its FDA-approved flagship drug Scenesse as a potential treatment to increase pain-free light exposure for patients with xeroderma pigmentosum.