Parkinson’s disease is a chronic, progressive disorder. Its characteristics tend to include tremor, rigidity, slowness of movement, and impaired balance. Around 1 million people in the United States and 10 million people throughout the world have the disease.
Parkinson’s results from a loss of nerve cells in a part of the brain called the substantia nigra. These cells produce dopamine, a chemical messenger, or neurotransmitter, involved in controlling movement. Most people with Parkinson’s are older than 50 when they receive the diagnosis, but some develop motor symptoms, involving problems with muscle control, at an earlier age.
Years before motor symptoms arise, other symptoms of Parkinson’s can appear, including a reduced sense of smell, constipation, mood changes, and REM sleep behavior disorder, which involves physically acting out dreams. The existence of these prediagnostic symptoms suggests that damage to dopamine-producing nerve cells begins long before the person experiences trouble with movement.
A new study — spearheaded by researchers from the La Jolla Institute for Immunology (LJI), in California — adds to evidence that the immune system may be responsible for the damage to nerve cells. The research, which appears in Nature Communications, also indicates that this autoimmune attack could start more than a decade before the person receives a Parkinson’s diagnosis.
The findings offer hope that doctors may be able to diagnose the disease earlier and that immunosuppressant treatment could slow, or even prevent, the loss of dopamine cells. “Once these cells are gone, they’re gone,” says Cecilia Lindestam Arlehamn, Ph.D., the first author of the study and an assistant professor at LJI. “So, if you are able to diagnose the disease as early as possible, it could make a huge difference.”
A 2017 study involving some of the same researchers was the first to suggest that autoimmunity plays an important role in the development of Parkinson’s disease. The team discovered that a protein called alpha-synuclein acts like a beacon for the immune system’s T cells, causing them to attack brain cells, and thus contributing to the progression of Parkinson’s.
Alpha-synuclein misfolds, forming toxic clumps in the dopamine-producing nerve cells of people with the disease. The clumps can accumulate, forming larger, distinctive masses called Lewy bodies.