For those of us with LRRK@2 genetic variants, it seems that a specific form of b12 (Adenosylcobalamin) helps to reduce the negative effects of the LRRK2 kinase protein:
"The team first studied LRRK2 in cultured cells and brain tissue and found that AdoCbl inhibited LRRK2 in the low micromolar range. They then genetically modified fruit flies and C. elegans worms—organisms that show neurological symptoms roughly analogous to human PD—to express the LRRK2 mutation and found that feeding them AdoCbl slowed the decline in dopamine activity in their brains, demonstrating that treatment with AdoCbl was able to reduce these deficits in a dose-dependent manner. Furthermore, they found that AdoCbl corrected abnormal dopamine transmission in cultured tissues from mouse models with the LRRK2 mutation."