Additionally, a defect in homocysteine methyltransferase or a deficiency of Vitamin B12 may lead to a so-called "methyl-trap" of tetrahydrofolate (THF), in which THF is converted to a reservoir of methyl-THF which thereafter has no way of being metabolized, and serves as a sink of THF that causes a subsequent deficiency in folate.[14] Thus, a deficiency in B-12 can generate a large pool of methyl-THF that is unable to undergo reactions and will mimic folate deficiency.