Mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes; a common type of mitochondrial myopathy (MM). MELAS is one of a group of rare muscular disorders called mitochondrial myopathies. It is caused by a defect in the gene encoding for certain proteins/components of the mitochondria and results in disorders in the brain and muscles. Characteristics of MELAS include stroke-like episodes, seizures, vomiting, hearing loss, and elevated lactate levels. Also referred to as mitochondrial myopathy, encephalomyopathy lactic acidosis, and stroke-like episodes.