Parkinson's disease is seen in the central nervous system, in the Basal Ganglia. Degeneration of or damage to or stoppage of nerve cells within the Basal Ganglia is the cause. The substantia nigra cells produce dopamine, a chemical messenger responsible for transmitting signals within the brain that stop muscle activity. Loss of the cells' dopamine causes neurons to fire without normal control, leaving patients less able to direct or control their movement. Their muscles are overused and tire out.
The effect of generational mutations in the LRRK2 gene are indirectly the greatest genetic contributor to Parkinson's disease discovered to date. Since its influence varies with regards to race, other genes must also be involved somehow. In the early 1980s, a group of heroin users in California took drugs from a batch contaminated with a substance called MPTP. After ingesting this chemical, the drug users were stricken with a form of Parkinson's disease that was primarily, if not exclusively, "environmental" in origin. What it did, they do not know.
No one has a medical cure for Parkinson's, so far. This comes from so many levels of indirection that the root cause has not been found. And they can't experiment.
As for Christians, though, we need to find those Christians who have Word of Knowledge or Word of Wisdom - because they prayed for them. We can consult the Maker of the system for what's involved and how to ask for healing. Then the proof is in praying for sufferers without their knowing and seeing what brings healing.
My latest theory is the muscle "turn up" ganglia are on one side of the brain and the "turn down" ganglia are on the other side of the brain. They are capable of generalizing their activation & relaxation of muscles and specifying which muscles to activate or relax. Rage & fear can generalize all the muscles for strength; the intellect and instincts can specify which muscles. The "turn down" ganglia will gradually relax the muscles down over a longer period.
Heavy exercise in a large amount of muscles for a short time will trigger the body to burn up fat to create muscles in all those areas for a day or two by keeping the muscles somewhat tense for that time. Heavy exercise on just a specific set of muscles causes a lot less of this effect.
edited: May 31, 2017 orderofsaintpatrick.org/heal/parkinsons.htm