People with Friedreich ataxia have lower than usual levels of cell-free mitochondrial DNA circulating in the bloodstream, but higher levels of nuclear DNA, a finding that might result in new biomarkers to monitor these patients in clinical trials.
Research in Friedreich ataxia would benefit from the existence of a non-invasive biomarker of disease severity or progression. In an earlier study, the research group at All India Institute of Medical Sciences noted that total circulating DNA was higher in patients compared to healthy individuals. In this new study, “Plasma circulating cell-free mitochondrial DNA in the assessment of Friedreich’s ataxia,“ published in the Journal of the Neurological Sciences, the team looked at specific types of DNA to determine if disease-specific patterns existed.
Cell-free DNA in the blood comes mainly from dying cells, and has been investigated in other progressive diseases characterized by cell death, such as Alzheimer’s and diabetes.
The study enrolled 21 Friedreich ataxia patients, and 21 healthy control individuals, examining their symptoms and measuring levels of frataxin and DNA. Enrolled patients had a mean age of 18.5 years.
Measurements revealed that nuclear DNA levels were about twofold higher in Friedreich ataxia patients, while mitochondrial levels were lower. Researchers, however, did not find any correlations between blood DNA levels and symptoms, the number of GAA repeats in the frataxin gene, or frataxin levels. The team also measured how the levels changed during a six-month period in 16 of the initial Friedreich ataxia participants. The group was divided in two, with nine people being given omega-3 fatty acids, known to enhance mitochondrial metabolism.
After six months, mitochondrial DNA levels among those receiving omega-3 had increased, while remaining stable in patients not given the supplement. No effect on nuclear DNA levels could be observed. Again, the team found no links to symptoms, which during this period continued to worsen, suggesting that a potential improvement in mitochondrial function was not enough to slow disease progression.
The lack of a link to symptom progression lessens the value of circulating mitochondrial DNA as a biomarker. But to better understand if and how mitochondrial DNA might mirror disease, the authors suggest that larger studies, exploring potential treatments, are necessary.