 And why do you believe it is on the upswing? Aging obviously contributes to it because the disease unfolds over decades. Much like smoking and lung cancer, you don't smoke a cigarette and then develop lung cancer. You need many decades of cumulative exposure and time for the disease to develop. And as we live longer, more and more of us will have time to manifest the classic symptoms of the disease, such as tremor and difficulty with balance and walking.