Other less common predisposing factors include Protein S deficiency, Factor V Leiden mutation, Antithrombin III deficiency, Antiphospholipid antibody syndrome (Anticardiolipin antibody) and Lupus anticoagulant.3,13 Several reported cases have however occurred in patients without any of these deficiencies.14,15. Here, PROS1 is linked to hereditary antithrombin deficiency.