I have a doctor who is quite knowledgeable about this. He tested me for this as part of his overall strategy for figuring out my tremor, found I had the mutation and promptly started me on B12 and Thorne's 5-MTHF (L-5-Methyltetrahydrofolate) 5 mg daily. I read somewhere about problems if taking too much of 5-MTHF and asked him at my last appt. He said, emphatically, don't worry about taking too much, the worry is that it is too little. Sometimes I give 10 mg.

I also make sure the multivitamin I take does not have the regular from of folate in it (which can be detrimental). Dr. Mercola puts out a food based one.