We need alpha-synuclein for a healthy brain. Misfolded alpha-synuclein, a prion, causes the issues. I really suspect we will see a vaccine in five to ten years to address this.

Prions are proteins that adopt alternative conformations that become self-propagating;

Just fascinating, I'll admit I have to read through this a few times to get a basic understanding. Lots to learn:

Alpha-synuclein is a member of the synuclein family, which also includes beta- and gamma-synuclein. Synucleins are abundantly expressed in the brain and alpha- and beta-synuclein inhibit phospholipase D2 selectively. SNCA may serve to integrate presynaptic signaling and membrane trafficking. Defects in SNCA have been implicated in the pathogenesis of Parkinson disease. SNCA peptides are a major component of amyloid plaques in the brains of patients with Alzheimer's disease. Alternatively spliced transcripts encoding different isoforms have been identified for this gene. SNCA synuclein alpha [Homo sapiens (human)] - Gene - NCBI