For example, hereditary risk factors involve homocysteinemia, factor V Leiden homozygous mutation, G20210A prothrombin gene and methylenetetrahydrofolate reductase 677TT mutations, protein C and S and anti-thrombin III deficiency, and positive anticardiolipin or antiphospholipid antibodies. The gene discussed is F2; the disease is hyperhomocysteinemia.