Carey,
Yes, I am suggesting that the BBB is the thing to concentrate on. Find a way to reduce the permeability and that will stop a lot of toxins getting in, like those proposed by Heidi, or toxins from helicobacter, or many other types, which circulate harmlessly in the blood stream of a healthy person. Possibly the symptoms of PD vary so much because it depends which toxin has succeeded in getting past the BBB.
I am certainly not saying Heidi is not correct in her proposal. Rather I am saying it is another example of a different toxins which get through a compromised BBB. However, if you have a sensitivity to gluten, and a defective BBB, you will show PD symptoms. If you don't have a defective BBB, only gluten sensitivity, you won't show PD symptoms.
The ideas proposed by Heidi are linked with a defective BBB therefore, but I don't want to divert the thread to the BBB, so I will open a new thread and summarise what I think. I believe the main test of any theory is it has to have answers for all questions and facts.
Heidi,
Yes, I agree, it has to be this and that, but the this is always a defective BBB. For example a defective BBB and gluten sensitivity. A defective BBB and toxins from helicobacter, a defective BBB and toxins from a virus, and so on. As I have said, your ideas are certainly not wrong, but it does need a defective BBB as well.
Prof Leenders found each of the PD people he examined all had a defective BBB. Have you got a reference to people with a damaged BBB not showing PD? It is of course possible to have mild damage to the BBB below the threshold needed to cause trouble and the first signs of PD.

Ron