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Cardiovascular Disease Risk Linked to mtDNA Copy Number

NEW YORK (GenomeWeb) – The lower one's mitochondrial DNA copy number, the greater one's risk for cardiovascular disease, according to researchers at Johns Hopkins University.

The JHU investigators reported their finding this week in JAMA Cardiology, backed by SNP array data from 21,870 participants culled from several large cardiovascular study groups, including the Atherosclerosis Risk in Communities Study (ARIC), the Cardiovascular Health Study, and the Multi-Ethnic Study of Atherosclerosis.

They now believe that by measuring mtDNA copy number, clinicians might be able to predict the risk of heart attacks and sudden cardiac events long before they occur, enabling them to better prescribe treatments.

Dan Arking, an associate professor of medicine at JHU School of Medicine and corresponding author on the paper, said in a statement that mtDNA copy number should be considered a risk factor for cardiovascular disease like LDL, total cholesterol, and blood pressure.

"It adds sensitivity and specificity to whether or not you should be taking a statin," he noted.

Arking's group has been investigating the link between mtDNA copy number and cardiovascular disease for years. The work is based on the premise that mitochondrial dysfunction is a component of the aging process and therefore may factor in cardiovascular disease. In February, it received an $800,000 National Institutes of Health grant to continue its research over the next five years. The JHU team has already published several papers on the topic, most recently in June in the European Heart Journal that established a relationship between low mtDNA copy number and sudden cardiac death in a cohort of 11,093 individuals from the ARIC study.

In the JAMA Cardiology study, the researchers assessed individuals' mtDNA copy number levels compared to nuclear DNA levels, and then added the difference as a risk factor to the Heart Risk Calculator, a method developed by the American College of Cardiology/American Heart Association that takes into account cholesterol, blood pressure, family history, smoking habits, and other lifestyle factors to predict the risk for experiencing a cardiac event within 10 years.

Using their mtDNA copy number data, plus the other factors, the JHU team was able to identify six people who would have not been recommended treatment under the standard calculation who eventually suffered near-fatal cardiac events. They also tagged 139 people who would have been recommended treatment according to guidelines, without the inclusion of mtDNA copy number data, and actually never had any cardiac events. They would have been medicated, even though the mtDNA copy number data suggested that there was no reason to prescribe them drugs.

"This is important," Arking said, "because though statins are great drugs and they clearly lower the risk of heart disease, there are side effects and costs associated with taking them, including muscle pain, liver damage, and neurological effects."

The researchers maintain that further study is necessary before mtDNA copy number can safely be introduced as a routine test for cardiovascular disease risk. They need to better understand healthy levels of mtDNA copy number across different age groups. However, based on their findings, they said it "may have potential clinical utility" in improving disease risk classification.