Thus, the genetic polymorphism MTHFR(677)C>T (rs1801133) is responsible for folate availability, and decreased MTHFR enzymatic activity, together with certain environment conditions during pregnancy such as poor nutrition, low folate intake, hyperhomocysteinemia and active or passive exposure to tobacco smoke, have been associated with an increased risk of different adverse birth outcomes [17,18,19]. The gene discussed is MTHFR; the disease is hyperhomocysteinemia.