TCN2 and cleft lip: Recently, many efforts have been made to find the genetic variants in folate pathway genes such as MTHFR (methylenetetrahydrofolate reductase), MTRR (Methionine synthase reductase), TCN2 (transcobalamin 2), and BHMT (betaine-homocysteine methyltransferase) and their susceptibility to cleft lip [4–10].