Recent research has shown that those with TCN2 776C→G polymorphism are prone to peripheral neuropathies and nerve damage when exposed to greater than 800mcg of folate per day. (See: https://www.ncbi.nlm.nih.gov/pubmed/27733392)
I've also had serious negative reactions to methylfolate, with two ER visits last year due to a 7-day trial of high MF intake (15mg). Nine months later, I am still experiencing symptoms from that misguided trial. MF is powerful, powerful stuff.
Interesting! I do wonder about the folate though, is it folic acid or methylfolate? There is a lot of research, but they rarely elaborate about the form of folate.
What kind of symptoms did you get from 15 mg methylfolate?