Although folic acid is stable and inexpensive, its metabolism poses certain limitations: it can mask vitamin B12 deficiency, and high intake may lead to circulating unmetabolized folic acid (UMFA), which has been associated with potential immune modulation and other health concerns.[13–16] Moreover, polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene are highly prevalent in the general population. The gene discussed is MTHFR; the disease is vitamin B12 deficiency.