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What is Mitochondrial Disease?
Mitochondria are present in all cells in the body (except for red blood cells). These tiny organelles contain their own DNA, and are responsible for carrying out certain essential cellular functions, including oxygen processing and energy synthesis. Mitochondria synthesize more than 90% of the energy the body uses.
Mitochondrial disease occurs due to genetic defects in mitochondrial or nuclear DNA that cause the mitochondria to fail in one or more cell types. There are actually more than forty different types of mitochondrial disease, each originating from a different genetic mutation. The common thread for each type is that the mitochondria are unable to synthesize energy. In some cases, toxic by-products may build up in the body, damaging mitochondrial DNA (which cannot repair itself the way nuclear DNA can) and causing even more damage.
Because there are more than forty types of mitochondrial disease, symptoms are wide-ranging. Symptoms may include poor growth and development, visual or hearing problems, muscle weakness and lack of coordination, learning disabilities, kidney, liver, or heart disease, respiratory disorders, gastrointestinal disorders, or neurological problems (such as seizures). The range of symptoms experienced by any one individual depends on the organs and systems affected by the disease.
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How can Stem Cells Treat Mitochondrial Disease?
Current treatments for mitochondrial disease focus mainly on treating symptoms and slowing down the disease’s progression. Common treatments include dietary therapy, vitamin supplements, and lifestyle changes to reduce physiological stress (such as that produced by extremes of heat and cold).
As with many other illnesses, stem cells may provide new options for treating many types of mitochondrial diseases. However, because each of the more than forty types of mitochondrial disease have different causes, it is not likely that one type of therapy will work effectively for all types of mitochondrial disease.
There is hope, however, for treatment of certain types of mitochondrial disease. At a meeting on mitochondrial diseases held in Phoenix, AZ in May 2008, researcher Michio Hirano of Columbia University in New York spoke of a possible treatment for mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), a type of mitochondrial disease caused by a genetic defect in a nuclear enzyme which is responsible for breaking down thymidine. The failure of the enzyme causes thymidine to accumulate in the blood, at levels which are toxic to mitochondria.
The experimental treatment for MNGIE developed by Dr. Hirano involves infusions of healthy blood stem cells, intended to restore function of the required enzyme, and eliminate thymidine toxicity. At the May 2008 meeting, Hirano reported that one patient, a thirty year old woman with MNGIE, had experienced a remarkable reduction in symptoms up to two and a half years after receiving donor blood stem cell infusions.