North American Mitochondrial Disease Consortium

Information for Patients and Families

Overview of Mitochondrial Diseases

What are Mitochondrial Diseases?

Mitochondrial Diseases are very diverse conditions due to dysfunction of mitochondria, specialized compartments (organelles) in virtually every cell of the body (only red blood cells lack mitochondria). Mitochondria generate more than 90% of the energy required by the body. Mitochondrial dysfunction depletes cells of energy causing cell damage and even cell death.

Due to the high energy requirements of brain and muscle, mitochondrial disease typically affect these parts of the body causing encephalomyopathies (brain and muscle disease). Other organs are frequently affected including: eye, ear (the hearing organ called the cochlea), heart, liver, gastrointestinal tract, liver, kidney, endocrine organs (such as the thyroid gland and insulin-producing cells in the pancreas), and blood.

Who gets Mitochondrial Diseases?

The diseases predominantly affect children, but adult-onset disorders are being recognized with increasing frequency.

What causes Mitochondrial Disease?

Mitochondria are unique organelles because they are the products of their own genetic material (mitochondrial DNA or mtDNA) and nuclear DNA. Therefore, mitochondrial diseases are caused by mutations in either mtDNA or nuclear DNA.

How are Mitochondrial Diseases diagnosed?

Mitochondrial diseases are often difficult to diagnose and therefore, it is important for patients to be evaluated at a medical center with appropriate expertise. In some cases, symptoms and signs may suggest a particular mitochondrial disease. Physical examination and laboratory tests are necessary to characterize involvement of various organs and to reach the correct diagnosis. Laboratory studies typically include: blood tests, brain MRI or CT scans, heart tests (electrocardiogram and echocardiograms), ophthalmological and neurological evaluations, and hearing tests. Elevated lactic acid (lactate) or lactate to pyruvate ratio (>20:1) in blood or cerebrospinal fluid is a common sign of mitochondrial dysfunction. Muscle biopsy is the gold-standard for the diagnosis of many mitochondrial diseases and requires specialized microscopic analyses and biochemical tests (such as measurements of mitochondrial respiratory chain enzyme activities). Finally, genetic testing of blood, urine, or muscle is performed to pinpoint the exact mutation responsible for a specific disease.

What is the treatment for Mitochondrial Disease?

Treatment of mitochondrial diseases is limited. Therapies to treat specific symptoms and signs of mitochondrial diseases are very important. For example, in mitochondrial patients, epilepsy typically responds to anti-convulsant drugs while insulin and other standard treatments are effective for diabetes mellitus. Nutritional supplements such as vitamins and co-factors are often taken by patients with mitochondrial diseases and are most useful in patients with specific deficiencies (e.g. coenzyme Q10 (CoQ10) supplementation is particularly effective in patients with CoQ10 deficiencies).