I am now in my late 60s, and have had Parkinson’s for 16 years now. Actually I have had PD for more than 30 years. By the time you get a diagnosis of PD, you have already lost about 85% of your dopamine producing neurons in your brain.
But researchers are speculating that PD start elsewhere: in the gut perhaps? They are already tracking different cells that are moving up the body and finally end up in the brain. And after these cells get to the brain, you get PD. That is the latest idea.