Diseases of childhood and young adulthood.
Most inherited maternally and involve multiple systems, with some sporadic cases.
May be at least as common i.e., 1 in 8500 population, as other sporadic and inherited neurological disorders, such as amyotrophic lateral sclerosis and Huntington’s chorea.
Symptoms as a result of dysfunction of tissues with high rate of oxidative metabolism including the brain and peripheral nerves, skeletal muscles, cardiac muscles, retina, renal tubules and organ of Corti of the inner ear.