PROS1 and deep vein thrombosis: Hereditary thrombophilia, such as that associated factor V Leiden and the prothrombin G20210A gene variant, has been reported in Caucasians, but such findings have not been reported in Asians.8) Conversely, protein S deficiency is more common in Japan than in other East Asian countries because of the protein S K196E mutation.9,10) In Japan, several case reports on DVT associated with pregnancy have been published, but there have been no comprehensive studies.