Test Details: Mitochondria Encephalopathy with Lactic Acidosis and Stroke-like Episodes (MELAS) is maternally inherited disorder characterised by stroke like episodes, encephalopathy with seizures and/or dementia and mitochondrial myopathy with multisystem involvement. The A3243G mutation in the t RNA leu (MTTL1) gene of mitochondrial DNA accounts for about 80% of MELAS cases and the remaining cases involve other point mutations. The age of onset and the clinical course of disease caused by mitochondrial mutations are highly variable due to mitochondrial heteroplasmy i.e. concurrent presence of wild type and mutant mitochondria in tissues and cells. The heteroplasmy also underlies the phenotypic variability characteristics of mitochondrial diseases.