Amount of mitochondrial DNA predicts frailty, mortality in humans

Chuck Bednar for redOrbit.com – Your Universe Online
The amount of mitochondrial DNA (mtDNA) found in a person’s blood could be used to predict his or her overall risk of frailty and death from any cause 10 to 15 years before the first symptoms appear, researchers from The Johns Hopkins University say in a new study.
Mitochondrial DNA, the cellular organelles that help convert food into chemical energy for cells, can be used to enhance our scientific understanding of aging, the study authors explained. Their findings, which were published online earlier this month in the  Journal of Molecular Medicine, could be used to develop a new test to identify at-risk individuals.
Dr. Dan Arking, an associate professor of genetic medicine at the university, said that he and his colleagues “don’t know enough yet to say whether the relationship is one of correlation or causation, but either way, mitochondrial DNA could be a very useful biomarker in the field of aging.” It could be used to identify people who could benefit health-wise from lifestyle changes.
Unlike other cell structures, mitochondria (which are also known as “power houses” since they are responsible for generating the majority of a cell’s energy) contain their own DNA separate from those enclosed in the nucleus. Their DNA comes in the form of between two and 10 small, circular chromosomes which code for 37 genes necessary for mitochondrial function.
Previous research from Dr. Arking’s laboratory has found a link between genetic differences in mtDNA and the reduced muscle strength and increased frailty experienced by older men and women. In medical terms, frailty refers to a highly recognizable set of aging symptoms, including weakness, decreased energy, reduced activity and weight loss, the study authors added.
In order to further study this correlation, the investigative team analyzed the amount of mtDNA in blood samples collected for a pair of large studies that began during the late 1980s. They monitored the health of individuals for up to 20 years and calculated the amount of mtDNA each sampled contained relative to the amount of nuclear DNA.
Dr. Arking and his colleagues then reviewed measures of frailty and health status gathered on the studies’ participants over time. They found that, on average, study participants that met the criteria for frailty had nine percent less mtDNA than nonfrail participants. Furthermore, white participants in the bottom one-fifth of the study population in terms of mtDNA were 31 percent more likely to be clinically frail than participants in the top one-fifth.
“The researchers also analyzed the age at which participants died. In one of the studies, high levels of mtDNA corresponded to a median of 2.1 extra years of life compared to those with the lowest levels of mtDNA,” the university said.
“Using data from both studies, the team found that those with mtDNA levels in the bottom one-fifth of the population were 47 percent more likely to die of any cause during the study period than were those in the top one-fifth,” the institution added. “They also found that women had an average of 21 percent more mtDNA than men.”
Dr. Arking explained that the link between decreased mtDNA and negative health outcomes should come as no surprise, since our energy reserve decrease as we age and we become more susceptible to disease and other ailments. He added that the gender-based finding could also help explain why women live an average of two to four years longer than men.
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