Test Details: Mitochondrial diseases are a clinically heterogenous group of disorders that arise as a result of dysfunction of the mitochondrial respiratory chain. Epidemiological studies have shown that mitochondrial disorders affect at least one in 8000 of the general population. The MITOMAP database has confirmed the association of the mitochondrial mutations with the pathogenesis of mitochondrial disorders. 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.