Mitochondrial Diseases Support Group

Mitochondrial diseases comprise those disorders that in one way or another affect the function of the mitochondria and/or are due to mitochondrial DNA. Mitochondrial diseases take on unique characteristics both because of the way the diseases are often inherited and because mitochondria are so critical to cell function. The subclass of these diseases that have neuromuscular disease symptoms are often referred to as a mitochondrial myopathy.

The effects of mitochondrial disease can be quite varied. Since the distribution of defective DNA may vary from organ to organ within the body, the mutation that in one person may cause liver disease might in another person cause a brain disorder. In addition, the severity of the defect may be great or small. Some minor defects cause only "exercise intolerance", with no serious illness or disability. Other defects can more severely affect the operation of the mitochondria and can cause severe body-wide impacts. As a general rule, mitochondrial diseases are worst when the defective mitochondria are present in the muscles or nerves, because these are the most energy-hungry cells of the body.

However, even though mitochondrial disease varies greatly in presentation from person to person, several major categories of the disease have been defined, based on the most common symptoms and the particular mutations that tend to cause them.

In addition to the Mitochondrial myopathies, other examples include:

* Diabetes mellitus and deafness (DAD)
o this combination at an early age can be due to mitochondrial disease
o Diabetes mellitus and deafness can be found together for other reasons as well

* Leber hereditary optic neuropathy (LHON)
o visual loss beginning in young adulthood
o Wolff-Parkinson-White syndrome
o multiple sclerosis-type disease

* Leigh syndrome, subacute sclerosing encephalopathy
o after normal development the disease usually begins late in the first year of life, but the onset may occur in adulthood
o a rapid decline in function occurs and is marked by seizures, altered states of consciousness, dementia, ventilatory failure

* Neuropathy, ataxia, retinitis pigmentosa, and ptosis (NARP)
o progressive symptoms as described in the acronym
o dementia

* Myoneurogenic gastrointestinal encephalopathy (MNGIE)
o gastrointestinal pseudo-obstruction
o neuropathy