Hi Joopoele,
Hoe gaat U?
"Homocysteine increases the BBB permeability", see
http://bloodjournal.hematologylibrar.../107/2/591.pdf
and "Elevated levels of homocysteine have been observed in Parkinson's disease (PD) patients treated with levodopa." see

http://www.sciencedirect.com/science...eca28b1d018ad2

Isn't this what we would expect, accoding to the theory. It is yet another example of substances that increase the BBB permeability, are associted with PD.
"Vitamin B12-B6-folate. treatment improves blood-brain barrier function"
so low levels would be expected to worsen PD symptoms.
You can only do a literature search and you will find ever more examples of the 2 classes of substance, those that widen the pores of the BBB cause worsening of symptoms. whilst those that reduce the porosity
improve symptoms.
Ron