Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome (MELAS) is a maternally inherited disorder caused primarily by a mutation in the tRNA of the MT-TL1 gene of mitochondrial DNA, accounting for ~80% of cases. Many other causal mutations have been found, most of which are mutations in tRNA genes, and all impairing mitochondrial protein synthesis. The pathogenesis of the stroke-like symptoms is not well understood; however, it has been proposed that those with MELAS may have impaired blood flow due to the overabundance of mitochondria in the small arterioles and capillaries of their neuro-vasculature, or impaired vascular metabolism.