I have MTHFR and seem to have a functional deficiency of B12. My level was greater than 2000 over a year ago without supplementation. I started treating it several months ago with methyl B12 and Dibencozide and symptoms have improved greatly. However, my levels remain unchanged. According to Dr. Yasko's B12 chart, I should be taking Hydoxy B12 with my particular SNP's. My serum iron level has also risen. I am hypothyroid and was told on my thyroid forum that using the wrong B12 (referring to methyl) could cause it to pool in my blood since my body couldn't use it. It could also cause serum iron to rise. Was told this info was gathered from Dr. Ben Lynch, Dr. Amy Yasko, and Dr. Amy Neuzil. However, I haven't been able to locate this particular information. Has anyone heard of this? When I try Hydroxy B12, I don't feel as well. My folate levels are normal.