Thrombophilia:its Causes and a Rough Estimate of Its Prevalence

Idiopathic venous thrombosis and embolism have gained widespread interest since the discovery that, deficiencies of antithrombin III, protein C, and protein S are associated with familial venous thrombophilia. The purpose of our study was to obtain an estimate of the prevalence of this syndrome and to establish the etiology in as many cases as possible. We collaborated with specialists from 37 Dutch hospitals, covering about 10% of the Dutch population. A history as well as blood samples were obtained from 113 unrelated cases with familial thrombophilia and from 90 isolated cases. Assuming that each proband in a family with thrombophilia has an average of four affected relatives, a rough estimate of the prevalence of familial thrombophilia in The Netherlands is 40 cases per 100.000. The prevalence of non-familial thrombophilia is probably lower. In 35 out of the 113 familial cases we established a diagnosis of hereditary antithrombin III deficiency (n=5), protein C deficiency (type I: n=9; type II: n=4), protein S deficiency (n=15) and dysfibrinogenemia (n=2). In 36 cases we found no abnormality at all and in the remaining 42 cases abnormalities were found in one or more of the following: heparin cofactor II, factor V, factor VII, factor VIII, von Willebrand factor, plasminogen, tissue plasminogen activator, plasminogen activator inhibitor, alpha 2 antiplasmin and histidine rich glycoprotein. In most of these cases, however, the hereditary nature of the abnormalities could not be demonstrated and the causal relationships remain to be established. In the 90 isolated cases, we diagnosed hereditary deficiencies of anti thrombin III, protein C and protein S each in one case and a lupus anticoagulant in two cases. In 54 cases no abnormality was found and in the remaining 31 cases various abnormalities were found in one or more of the proteins mentioned above. We conclude that the syndrome of thrombophilia is not rare but its true prevalence needs to be established by more rigorous means. An etiological diagnosis can be made with confidence in only one third of the familial cases and in less than 10 percent of the isolated cases.