When I was fourteen years-old, I was hit by a car going 45 MPH and was knocked unconscious for two days. Last year, at age 36, I was diagnosed with early-onset PD.
I've spoken with two other early-onset PD patients in the last month and they both had a serious head injury / trauma when they were younger.
I'm not sure if there is any connection, but it made me wonder. Anyone else, who is early-onset PD, have a prior head trauma / accident?