Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes (MELAS) is a progressive neurodegenerative disorder that is inherited in a mitochondrial pattern.  MELAS is characterized by acute neurological episodes resembling strokes associated with hyperlactatemia and mitochondrial myopathy.  While all mitochondrial diseases occur in about 1 in 4,000 people, the exact incidence of MELAS is unknown.  Patients usually present during childhood or early adulthood with acute crises with a wide variety of clinical presentations.

The typical presentation of patients with MELAS syndrome includes: mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes.  Other features may include: seizures, diabetes mellitus, hearing loss, cardiac disease, short stature, endocrinopathies, exercise intolerance, and neuropsychiatric dysfunction.  The diagnosis of MELAS is based on the clinical findings, brain imaging, and molecular genetic testing.  There is no specific treatment for MELAS.  Some patients may be treated with supportive treatments including coenzyme Q10, or with deleterious impact of treatment such as valproic acid.

Mutations in several mitochondrial genes are the cause of MELAS, including MT-ND1, MT-ND5, MT-TH, MT-TL1, and MT-TV genes.  More than 10 different mutations have been identified, but 80% of the cases are due to the 3243A>G mutation in the leucine transfer RNA gene (tRNA Leu).  These mutations affect mitochondrial tRNA function, leading to the disruption of the global process of intramitochondrial protein synthesis.  Mutation 3271 T>C in the tRNA Leu gene is associated with 7.5% of the cases.