Abstract: The present invention relates to a method and manufacture for detecting neuromuscular disease, particularly Myoclonic Epilepsy and Ragged Red Fiber disease, by ascertaining whether a transition mutation has occurred at the 8344 nucleotide position in the mitochondrial DNA of a patient. The invention provides methods to detect this mutation including digestion of the patient's mtDNA with restriction endonucleases followed by analysis of the resulting fragments, differential hybridization of oligonucleotides, direct PCR sequencing and denaturing gradient gel electrophoresis.