Mitochondrial myopathies are caused by mitochondrial mutations, and they refer to a group of diseases that include MELAS and MERRF. Since the mitochondria are inherited from the mother, this means that the mitochondrial myopathies are maternally inherited disorders. The damaged mitochondria lead to a disruption in oxidative phosphorylation, thereby leading to a disruption in aerobic metabolism and subsequent lactic acidosis. On biopsy, you’ll be able to recognize the presence of ragged red fibers, which is caused by the accumulation of diseased mitochondria in the subsarcolemma of muscle fibers. Signs and symptoms include CNS disease, such as epilepsy and seizures.