 The minor ( " type 2 " ) thrombophilias are much more common . Factor V Leiden is present in 5 % of the population of Northern European descent , but much rarer in those of Asian or African extraction . In people with thrombosis , 10 % have factor V Leiden . In those who are referred for thrombophilia testing , 30 – 50 % have the defect . The prothrombin mutation occurs at rates of 1 – 4 % in the general population , 5 – 10 % of people with thrombosis , and 15 % of people referred for thrombophilia testing . Like factor V Leiden , this abnormality is uncommon in Africans and Asians . 
