Introduction: Recently the molecular basis of a series of clinical disorders associated with defects in the oxidative phosphorylation system (OXPHOS system) leading to ATP synthesis, the final pathway of mitochondrial energy metabolism, has been established. The polypeptide components of the OXPHOS system are codified in both nuclear and mitochondrial DNA. Therefore these mitochondrial diseases may be originated by mutations of genes found in both genetic systems.
Development: In recent years, several such neuromuscular diseases have been defined and associated with mitochondrial DNA mutations. One of the most striking of these is the syndrome of myoclonic epilepsy with ragged red fibres (MERRF), characterized by myoclonic epilepsy of maternal inheritance. This disorder is caused by a specific mutation on the mitochondrial tRNA(Lys) (position 8344), which gives rise to a reduction in the level of lysil-tRNA(Lys) and thus to premature termination of the translation of proteins codified in the mitochondrial DNA.