Mitochondria, which are found in all cells in the body, use food and oxygen to produce energy. The result is often muscle weakness, fatigue, and problems with the heart, eyes, and various other systems. Mitochondrial myopathies are typically caused by defects in a part of the mitochondria called the respiratory chain. If there is a deficiency in any of these complexes, the individual will have mitochondrial myopathy.
Mitochondrial myopathies are typically inherited disorders.
That is, they are passed on from parent to child. Symptoms and severity are consistent within family members. The mtDNA defect can only be passed on by the mother. Symptoms and severity are not consistent within family members because the ratio of mutated cells to normal cells can vary greatly from one pregnancy to another. This mutation is said to occur in the early development of the embryo.