Contributor: Edward H. Bossen
MERRF (myoclonic epilepsy with ragged-red fibers) is a rare familial disorder with varying clinical manifestations within the same family. The designation MERRF is an acronym for Myoclonic Epilepsy with Ragged-Red Fibers. Many have a point mutation at nt 8344 in mitochondrial DNA. Gomori trichrome staining of frozen sections of the muscle biopsy reveals ragged-red fibers. Mitochondria are red with this stain and when there are aggregates of mitochondria they produce a ragged appearance in the muscle fiber with areas of green myofibrillar staining and red mitochondrial staining. Cytochrome oxidase staining will reveal that a portion of the fibers do not have cytochrome oxidase activity. The disease has a wide range of severity. The clinical onset may begin in childhood or during adult life. Some family members have no clinical manifestations while others have a rapidly progressive course to death. The clinical picture may include myoclonic epilepsy, dementia, hearing loss, and cardiomyopathy. The course is related to the severity of the mitochondrial abnormality and the degree of loss of mitochondrial energy output. Biochemical studies show a variety of abnormalities of the respiratory chain complexes.