Biological risk factors include protein C, protein S, and antithrombin III deficiencies; Factor II or Factor V mutations; hyperhomocysteinemia linked to a homozygous mutation in the MTHFR gene; homozygous sickle cell disease; anticardiolipin antibodies; and circulating lupus anticoagulant in the mother's blood which is transmitted to the fetus in utero [4–6]. Here, PROS1 is linked to sickle cell disease.