MTHFR and hyperhomocysteinemia: The most common genetic defect that can cause hyperhomocysteinemia is the MTHFR gene C677T polymorphism: the prevalence of such homozygotes in Europe can reach 20% while the frequency of heterozygotes is calculated as 30–40%, resulting in a reduction of the corresponding enzyme that can be responsible for a slight to moderate hyperhomocysteinemia [14].