Factor V Leiden: who should be tested?

Resistance to activated protein C resulting from the genetic point mutation known as factor V Leiden is the most frequently found genetic risk factor associated with familial predisposition to venous thrombosis. Factor V Leiden is also frequent among people with nonfamilial venous thrombosis and appears to have a relatively high prevalence rate in the general population. The author comments on the findings of the first Canadian prevalence study of factor V Leiden, reported in this issue by Dr. David H. Lee and associates (see pages 285 to 289). She notes that although certain hereditary and clinical variables are known to modulate the risk of venous thrombosis in people with factor V Leiden, explanations for the relatively high prevalence of this mutation and the wide spectrum of risk associated with it are still speculative. Management guidelines for affected patients are quickly evolving but are still limited by a lack of clinical data. It is clear that further research into factor V Leiden will have considerable importance for the understanding and management of thrombotic risk.