PROS1 and transient ischemic attack: In patients with ischemic stroke or TIA of unknown source with no other thrombotic history and who are found to have prothrombin 20210A or factor V Leiden mutation, elevated factor VIII levels, deficiencies of protein C, protein S, or antithrombin, or isolated antiphospholipid antibody without fulfilling the criteria of antiphospholipid syndrome, antiplatelet therapy is reasonable to reduce the risk of recurrent stroke or TIA (AHA/ASA: COR IIa, LOE C-LD) (Kleindorfer et al., 2021).