People with Parkinson’s disease have decreased amounts of mitochondrial DNA (mtDNA) both in the blood and the brain, researchers from the University of Newcastle Upon Tyne, U.K., reported in a study published in the journal Neurobiology of Aging.
In the study, titled “Reduced mitochondrial DNA copy number is a biomarker of Parkinson’s disease,“ the research team analyzed blood samples from 363 individuals with Parkinson’s disease and 262 matched controls with no clinical signs of the disease. All participants underwent a cognitive assessment and were screened for known mutations affecting cognitive function.
Researchers also analyzed brain tissue from diseased individuals, both with and without Parkinson’s disease. The team had access to samples of a brain area called substantia nigra from 151 patients and 33 controls, and from the frontal cortex brain region of another 120 patients and 37 controls. Substantia nigra harbors the cell bodies of dopamine-producing nerve cells that degenerate in Parkinson’s disease, and the frontal cortex is crucial to cognitive abilities.
Measurements of mitochondrial DNA amounts revealed substantially lower mtDNA levels in the white blood cells of Parkinson’s patients in comparison to blood samples from controls. This reduction was also found in the disease-affected brain region substantia nigra, but not in the prefrontal cortex.
While no link between smoking and Parkinson’s diagnosis could be detected, the team observed reduced mtDNA amounts in blood samples from Parkinson’s patients with a history of smoking. The team also reported no associations between blood mtDNA levels and cognitive measures.
Considering the study design, it is not possible to exclude that the differences between patients and controls are a result of medication or difficulties in accurately assessing mtDNA copy numbers. Studies following patients over time might help to better clarify the situation.
The authors suggested that low blood mtDNA levels could be used as a biomarker for Parkinson’s disease onset. Studies, however, have shown that other neurodegenerative diseases such as Huntington’s and Alzheimer’s diseases show similar features. More research is needed to investigate if blood mtDNA levels differ between these conditions, or if mtDNA reduction is a general hallmark of neurodegeneration.