Myoclonus epilepsy and ragged-red fiber (MERRF) syndrome is one of the common etiologies of progressive myoclonus epilepsy. The clinical features of MERRF syndrome are myoclonus, seizure, dementia, ataxia, neuropathy, myopathy, deafness, and
lipoma. The
patients with MERRF syndrome have a point mutation in mitochondrial DNA at 8344 or 8356 nucleotide. We are reporting a patient who developed myoclonus and seizure at the age of eighteen. He later showed cerebellar ataxia, peripheral neuropathy,
and
cognitive dysfunction. Skeletal muscle biopsy failed to demonstrate ragged-red fiber. He was diagnosed as MERRF syndrome by the mitochondrial DNA analysis. He had 86% mutant mitochondrial genomes(A→G(8344) mutation) in leukocytes, and his
asymptomatic
mother had 66%. The absence of ragged-rad fibers does not rule out the possibility of MERRF syndrome. Demonstration of mitochondrial DNA mutation is the most convincing method for establishing the diagnosis of MERRF.
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