Blood Test Clues: Mitochondrial DNA Distinguishes Parkinson’s From Look-Alike Disorder

Two devastating movement disorders, Parkinson’s disease and multiple system atrophy, often look so similar in the clinic that even experienced neurologists struggle to tell them apart in the early stages. Both belong to a family of conditions called alpha-synucleinopathies, in which a misfolded protein called alpha-synuclein accumulates in the nervous system and drives progressive neurodegeneration. Yet beneath that shared molecular signature, the two diseases follow distinct pathological paths, and the treatments and prognoses differ dramatically. Now a team of Italian researchers reports that a simple blood measurement may help separate them: the copy number of mitochondrial DNA in whole blood, a proxy for the energy-producing machinery of our cells, appears to distinguish Parkinson’s disease from multiple system atrophy far more sharply than another widely studied marker of biological aging, telomere length.

The study, published as a short commentary in the Journal of Neurology, comes from a group led by Monica Gagliardi of the Neuroscience Research Center at Magna Graecia University in Catanzaro, in the southern Italian region of Calabria. The researchers measured two molecular features in whole blood from 58 patients with Parkinson’s disease, 35 patients with multiple system atrophy, and 62 healthy controls drawn from the same region. The first feature was the copy number of mitochondrial DNA, estimated by quantifying the mitochondrially encoded NADH dehydrogenase 1 gene, known as ND1, relative to the nuclear beta-actin gene. The second was telomere length, the protective caps at the ends of chromosomes that erode with each cell division and are widely regarded as a cellular clock of aging.

The technical approach relied on quantitative PCR, the workhorse method for amplifying and measuring specific DNA sequences. By comparing the abundance of a mitochondrial gene to a single-copy nuclear gene, the team obtained a relative estimate of how many mitochondrial genomes each blood sample carries per cell. Telomere length was measured with the same technique, comparing the amount of telomeric DNA to a reference gene. To guard against spurious results, the researchers applied multivariable linear regression adjusted for age and sex, two factors known to influence both mitochondrial DNA copy number and telomere length, and they demanded that findings survive correction for multiple comparisons using false discovery rate-adjusted Wald tests, a statistical safeguard that reduces the risk of false positives when many hypotheses are tested at once.

The results were striking. Mitochondrial DNA copy number, as indexed by the ND1 gene, was significantly reduced in both patient groups compared with healthy controls, with a false discovery rate-adjusted p-value of 1.63 times ten to the power of minus twenty-two for Parkinson’s disease and 2.56 times ten to the power of minus eight for multiple system atrophy. More importantly for the question of diagnosis, the marker also separated the two diseases from each other: Parkinson’s patients showed significantly lower ND1 copy number than multiple system atrophy patients, with an adjusted p-value of 8.43 times ten to the power of minus twenty-two. In a field where biomarkers that cleanly discriminate between overlapping neurodegenerative conditions are desperately scarce, a difference of that statistical magnitude in a peripheral blood test is remarkable.

Telomere length told a related but subtly different story. Both patient groups again showed significantly shorter telomeres than the controls, with adjusted p-values of 3.21 times ten to the power of minus sixteen for Parkinson’s disease and 1.44 times ten to the power of minus twelve for multiple system atrophy. But when the researchers compared the two patient groups directly against each other, the difference was far weaker, reaching only the threshold of statistical significance with an adjusted p-value of 5.47 times ten to the power of minus two. In other words, telomere shortening appears to be a shared feature of both alpha-synucleinopathies, a general signature of accelerated cellular aging, whereas mitochondrial DNA copy number carries disease-specific information that could, in principle, help clinicians tell the two conditions apart.

Why would mitochondrial DNA copy number be depleted in the blood of patients with these brain diseases? The answer likely lies in the intimate relationship between mitochondria and neurodegeneration. Mitochondria are the organelles that generate most of the chemical energy a cell needs, and they carry their own small circular genome, separate from the DNA in the nucleus. Cells adjust the number of mitochondrial genomes they harbor in response to energy demands and stress. Decades of research have implicated mitochondrial dysfunction in Parkinson’s disease, from studies showing impaired mitochondrial respiration in the blood cells of people with early and even prodromal Parkinson’s, to work demonstrating mitochondrial defects in the fibroblasts of patients with multiple system atrophy. Previous studies have also reported reduced mitochondrial DNA copy number as a biomarker of Parkinson’s disease, although the picture is complicated: some investigations, including one in individuals of African ancestry, found increased blood-derived mitochondrial DNA copy number, and recent work has even documented elevated mitochondrial DNA copy number in the cerebellum of people with Parkinson’s. The direction and meaning of the signal may depend on tissue, disease stage, ancestry, and the specific cell populations being counted.

That last caveat is an important one. Whole blood is a mixture of cell types, and different immune cells carry different amounts of mitochondrial DNA. Recent research has suggested that differences in the abundance of peripheral immune cell populations may link blood mitochondrial DNA copy number to Parkinson’s disease, meaning that what looks like a mitochondrial defect could partly reflect shifts in blood cell composition driven by inflammation. Neuroinflammation is increasingly recognized as a player in both Parkinson’s disease and multiple system atrophy, so the reduced copy number observed in this study could reflect either genuine mitochondrial depletion within cells or an altered mix of circulating leukocytes, or both. The authors themselves frame their findings as preliminary and call for longitudinal studies in larger, independent cohorts to validate the diagnostic and prognostic utility of the marker before it could enter clinical practice.

The telomere findings also fit into a rich and sometimes contradictory literature. Telomere dysfunction is known to trigger metabolic and mitochondrial compromise through a stress-response network involving the p53 protein, creating a mechanistic bridge between the two markers measured in this study. Mouse experiments have shown that telomere shortening accelerates synucleinopathy and impairs the response of microglia, the brain’s immune cells, in genetic models of Parkinson-like disease. Human studies of leukocyte telomere length in Parkinson’s disease have produced mixed results over the years, with some groups reporting shorter telomeres in patients, others finding no difference, and longitudinal work suggesting that longer telomeres at diagnosis may paradoxically predict faster progression to dementia in idiopathic parkinsonism. A recent prospective analysis of the UK Biobank linked leukocyte telomere length to the risk of neurodegenerative diseases more broadly, reinforcing the idea that biological aging markers capture something real about vulnerability to these conditions, even if the details remain contested.

What makes the new study noteworthy is not any single result but the head-to-head comparison of the two markers within the same cohort, using the same methods and the same statistical framework. By showing that mitochondrial DNA copy number separates Parkinson’s disease from multiple system atrophy while telomere length does not, the researchers provide a concrete argument for prioritizing mitochondrial DNA copy number as a non-invasive, blood-based biomarker of disease-specific mitochondrial alterations in alpha-synucleinopathies. If the finding holds up in larger and more diverse populations, it could eventually help solve one of clinical neurology’s persistent puzzles: distinguishing Parkinson’s disease from multiple system atrophy early in the disease course, when the distinction matters most for counseling patients, planning treatment, and selecting the right participants for clinical trials of disease-modifying therapies. For now, the measurement requires nothing more exotic than a blood draw and quantitative PCR, a combination that, if validated, would make this one of the most practical biomarker candidates to emerge from the intersection of mitochondrial biology and neurodegeneration research.

Subject of Research: Mitochondrial DNA copy number and telomere length as blood biomarkers in Parkinson's disease and multiple system atrophy

Article Title: Preliminary insights into whole-blood mitochondrial DNA copy number and telomere length in Parkinson’s disease and multiple system atrophy

Article References: Preliminary insights into whole-blood mitochondrial DNA copy number and telomere length in Parkinson’s disease and multiple system atrophy. (n.d.). https://doi.org/10.1007/s00415-026-14172-7

Image Credits: AI Generated

DOI: 10.1007/s00415-026-14172-7

Keywords: Parkinson's disease, multiple system atrophy, mitochondrial DNA copy number, telomere length, alpha-synucleinopathies, biomarkers, neurodegeneration, mitochondrial dysfunction, quantitative PCR, cellular aging, blood biomarker, Journal of Neurology