The cause of Parkinson’s disease, a disorder of the nervous system that affects movement and motor control, is unclear. There is some evidence pointing to a genetic link, but plenty of people have Parkinson’s disease without any sort of family history of the condition, and the mutations known to cause the condition show up only in a small minority of patients. Some genetic markers are associated with a higher risk, but not much higher. Environmental factors, similarly, are known to increase the risk of Parkinson’s disease, but not by a lot, and not very consistently. Clumps of protein called Lewy bodies are found in the brains of patients with Parkinson’s. Lewy bodies are also found in patients with certain types of dementia—Parkinson’s does not usually cause cognitive impairment—and are considered the best bet for zeroing in on the cause of the illness.
Inside those Lewy bodies there is a protein called alpha-synuclein, which normally resists agglutination. However, alpha-synuclein is so closely linked with Parkinson’s that many doctors believed it was a factor in causing it. Now researchers in Chicago have found strong evidence that this protein overruns cells in much the same way viruses invade them.
The difference is that alpha-synuclein is already in the cell, in a part called the lysosome, where it performs important cellular functions. Problems arise when a virus breaks into the cell; Parkinson’s is a condition that scientists now believe can result when alpha-synuclein breaks out of the lysosome. Cells in which the lysosome has ruptured become inactive, in a process called apoptosis. Normally this is defensive, because lysosomal ruptures are usually caused by microbes, but when it is caused by alpha-synuclein, the effect kills an otherwise healthy cell.
Medications to treat Parkinson’s currently focus on a hormone called dopamine, one function of which is control of motion. The brain is induced to either produce more dopamine or make better use of that which it already has. However, this new research may help lead to the development of medications that target Lewy bodies directly.