PROS1 and Cowden syndrome 1: The prevalence of heterozygous FVL and prothrombin variant G20210A in patients with CS, was similar to that in the general population, regardless of the occurrence of VTE (10%–25% in case of VTE and 4%–6% without VTE) (29, 33), with no severe thrombophilias (i.e. antithrombin, protein C or protein S deficiency) (23).