Pulmonary embolism (PE) and deep venous thrombosis (DVT) are often regarded as two aspects of the same disease. Indeed, 50–70% of patients with DVT have evidence of silent PE and DVT is present in 70–90% of patients presenting with PE.1-5 This analysis may therefore be largely true, but there may also be important reasons—some of them genetic—why some patients present with DVT, some with PE, and others with signs of both. This problem will be discussed at the end of this review. In any event, most studies investigating possible genetic predispositions to venous thrombosis have either concentrated on DVT—for example, the Leiden thrombophilia study6—or have not made any distinction between DVT and PE.7-9 We therefore have to rely on these data to indicate the role of genetic variation in pulmonary embolism.

A genetic tendency to thromboembolism is also referred to as inherited thrombophilia and, although traditionally regarded as monogenic, it is undoubtedly a polygenic abnormality.10 ,11 The basis of our understanding of the thrombophilic state is that it arises from an imbalance between the procoagulant and anticoagulant components of the coagulation system, resulting in an increased tendency to thrombosis. This tendency usually becomes manifest as thrombosis as a result of its interaction with numerous environmental and acquired factors.