The SND victims ranged in age from 18 to 70 years old. None of the victims were engaged in intensive physical activity when they died. Causes of death in the control samples consisted of suicides, murders, or accidents. Genomic DNA was isolated from approximately 250 mg of cardiac muscle by a sodium dodecyl sulfate--proteinase K digestion at 56 degrees C overnight, and DNA was purified further by solvent extraction. Extracted DNA was quantified by spectrophotometric analysis. Findings indicate that samples from SND had a significant increased percentage of mtDNA4977-depletion compared with the control sample. The extent of dysfunction from mtDNA4977-deletion varies depending on the aerobic energy requirements of each tissue; this explains why tissues with high energy demands, such as cardiac muscle, are more often affected by mitochondrial defects. Large-scale rearrangement of mitochondrial DNA has been identified in patients with cardiomyopathy as a main clinical feature and associated with disorders of cardiac energy metabolism. In addition, the increase in susceptibility of cardiac tissue to DNA damage could lead to ischemic heart disease. This may be associated with the high incidence of SND among coronary artery disease patients. The findings of this study had not been previously associated with SND, so the findings should be confirmed in a larger sample size. 3 tables, 1 figure, and 27 references