Mutation of the methylenetetrahydrofolate reductase (MTHFR) gene in humans decreases the activity of the MTHFR, which causes a reduction in the content of L‐5‐MTHF in the body and increases the concentration of plasma homocysteine, leading to hyperhomocysteinemia (Boyi et al., 2013). Here, MTHFR is linked to hyperhomocysteinemia.