A potential blood test for Parkinson’s disease

In Parkinson’s disease, neurons that normally produce a compound called dopamine start to die in the part of the brain that controls movement. This eventually leads to symptoms such as shaking, stiffness, and difficulty with balance and coordination.

Some drugs used to treat the condition boost dopamine levels. These can relieve symptoms for a while, but they don’t slow progression of the disease and eventually stop working. New treatments for Parkinson’s disease are badly needed.

The lack of simple blood tests to diagnose Parkinson’s disease early, before extensive damage occurs, has hampered drug development. Recent research has suggested that Parkinson’s disease is likely a group of disorders with different causes, which end up causing similar damage but may need different treatments.

One likely cause of Parkinson’s disease in some people is damage to neurons’ mitochondria—the structures within cells that produce energy. To effectively test drugs that boost mitochondrial function, an assay to identify people whose disease is driven by mitochondrial damage would be needed.

In a new study, an NIH-funded research team led by Dr. Laurie Sanders from Duke University developed a blood test to detect damage to the DNA in mitochondria, called mtDNA. They built their test, which they call Mito DNA_DX, on polymerase chain reaction, or PCR, technology. Results were published on August 30, 2023, in Science Translational Medicine.

Initial results showed that Mito DNA_DX could detect mtDNA damage that more conventional assays could not. The test then found that mtDNA damage was elevated in cells taken from the blood of people with Parkinson’s disease compared with people without the condition.

Mito DNA_DX detected mtDNA damage both in people with a rare genetic mutation known to cause Parkinson’s and in those with the disease who didn’t have any known genetic risk factors. It worked whether or not people were currently taking medications to treat Parkinson’s. The test results were also consistent over time. Finally, the researchers calculated a cutoff value for mtDNA damage that effectively separated people with Parkinson’s disease from healthy volunteers.

Further experiments showed that the abnormal activity of a protein called LRRK2 kinase increased levels of mtDNA damage. Decreasing abnormal LRRK2 activity is currently a target of drug development for Parkinson’s disease. Therefore, Mito DNA_DX might be used to monitor treatment effects in real time.

“Our hope is that this assay could not only diagnose Parkinson’s disease, but also identify drugs that reverse or halt mitochondrial DNA damage and the disease process,” Sanders says. “This disease takes a terrible toll on people, and we are still just treating the symptoms. It’s important to get new, effective treatments over the finish line.”

Further research is needed to validate the test in larger, more diverse populations. Longer-term studies are also needed to see if mtDNA damage changes as Parkinson’s disease progresses. In addition, mtDNA damage is not unique to Parkinson’s disease. Researchers are working on other ways to diagnose and track Parkinson’s disease that may prove to be more specific for the disease.

—by Sharon Reynolds