Myoclonus epilepsy with ragged red fibers and multiple mtDNA deletions.

In a patient with clinical features of myoclonus epilepsy with ragged red fibers (MERRF), molecular genetic analysis of mitochondrial DNA did not show either of the two point mutations typically associated with MERRF but did show multiple deletions by Southern blot. This case further illustrates the heterogeneity observed with mtDNA mutations.