We may be able to get an indication of whether filtering alpha-synuclein out of the body can reduce PD without testing it directly. There are three classes of people who have had related experiences:

- healthy people who have has transfusions of blood from donors with Parkinson's. If there is something in the blood of PwP that can "infect" someone, these people would be expected to have an increased chance of getting PD. It is reported [1] that there is no evidence of this:

"A retrospective study of nearly 1.5 million patients over the course of 44 years showed no evidence to support the claim that neurodegenerative disorders can be transmitted between individuals through blood transfusions."

- people with Parkinson's who had blood transfusions of healthy blood. These PwPs would be expected to have slower progression. Olsen asked the question "Fresh Blood Transfusion a possible treatment?" in a 2014 thread [2]:

"old mice get better at learning and remembering when they have young blood circulating in their brains."

- people on dialysis already have their blood filtered now. Does this capture alpha-synuclein? If it does, the hypothesis would be that dialysis would lead to a decreased chance of PD and a slower progression

Of course, these interventions involve more than alpha-synuclein, and by the very ad hoc nature of these events they are not best able to detect changes. That said, just one case study linking these effects would be interesting.

References:

[1] No evidence to show Alzheimer’s or Parkinson’s transmission via blood transfusion | Clinical Neurology News

[2] Fresh Blood Transfusion a possible treatment?

John