ABSTRACT
Inheritance of myoclonic epilepsy with ragged red fibers disease (MERRF) is maternal; the mutations are predominantly in the mitochondrial gene for the tRNA for lysine. Patients with MERRF have also been reported to have defects in complexes II and III. In MERRF, the rule is for heteroplasmy for the mutation, and there is enormous variation within kindreds in the amounts of mutated DNA and even among tissues in a patient. The MERRF 8344 mutation has been shown to interfere with mitochondrial protein synthesis. Microinjection of human mitochondria permits growth in the absence of uridine, but cells receiving the MERRF 8344 mutation have markedly deficient synthesis of mitochondrial DNA, while those receiving normal mitochondrial DNA synthesize mitochondrial protein well. Family members at risk for maternally inherited MERRF may be tested for the mutation. Most often this is done on blood in those without symptoms. Examination of muscle may be required in those with any symptoms.
