Factor V:Q506 mutation-resistance to activated protein C (APC): clinical implications with respect to family screening.

Resistance to activated protein C (APC), which is almost exclusively caused by a point mutation in the factor V gene (FV:Q506 mutation or FV Leiden) is a recently discovered, prevalent risk factor for the occurrence of venous thromboembolism. It is unknown whether relatives of known patients with this mutation should be screened for the presence of the mutation and what the consequences for asymptomatic carriers would be. This paper addresses the possible benefits and disadvantages of family screening of patients with venous thromboembolism who carry the mutation. Possible prophylactic strategies are discussed and weighed on the basis of estimated incidence rates of venous thromboembolism that are deduced from known relative risks and available population studies.