MTRR and folate deficiency: Folic acid deficiency is usually caused by insufficient intake of folic acid as well as an insufficient ability to metabolize folic acid due to individual genetic causes.[5] The complex process of folate metabolism requires adequate activity of many enzymes and presence of co-enzymes.[6] The key enzymes in folate metabolism are 5,10-methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR).