MTR and hyperhomocysteinemia: Hyperhomocysteinemia may result from genetic defects in the enzymes involved in homocysteine metabolism: cystathionine ß-synthase (CBS), methionine synthase (MS), and N5,N10-methylenetetrahydrofolate reductase (MTHFR) or from deficiencies of enzymes cofactors (vitamin B6, vitamin B12, or cosubstrate vitamin B9) [5].