Interesting article but I think things can move along faster!
Researchers are reasonably sure that the accumulation of a protein called alpha-synuclein is responsible for neurons dying in people with PD. However, there are two competing theories as to how it builds up and spreads, the threshold theory and the ascending theory (also called the prion hypothesis). The ascending theory states that alpha-synuclein spreads from cell to cell, ‘infecting’ cells as the protein moves up through the brain. The threshold theory recently put forward by Dr. Ole Isacson and Dr. Simone Engelender, proposes that alpha-synuclein builds up independently in each affected cell.