MTHFR and vitamin B12 deficiency: Mild HHcy (plasma homocysteine concentrations 15–30 μM) develops due to genetic deficiencies or polymorphisms in cystathionine-β-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR), folate and vitamin B12 deficiency, and a methionine-rich meat diet (Tyagi et al., 2005; Sen et al., 2010).