Mitochondrial myopathies are a group of neuromuscular diseases caused by damage to the mitochondria—small, energy-producing structures that serve as the cells’ “power plants.” Nerve cells in the brain and muscles require a great deal of energy, and thus appear to be particularly damaged when mitochondrial dysfunction occurs
Symptoms include muscle weakness, heart failure, dementia, blindness, droopy eyelids, etc.
Mitochondrial Disease. MedicineNet. https://www.medicinenet.com/mitochondrial_disease/article.htm#what_is_the_prognosis_for_mitochondrial_disease