Thrombi may be caused by atherosclerotic disease or may be due to collagen-vascular disease, as in systemic lupus erythematosus, inflammatory conditions, as in giant cell (temporal) arteritis, polyarteritis nodosa, Behcet disease, and syphilis, or hypercoagulable states such as polycythemia vera, sickle cell anemia, multiple myeloma, factor V Leiden, and antiphospholipid syndrome. This evidence concerns the gene F5 and acquired polycythemia vera.