Factor V Leiden Thrombophilia is the most common inherited disorder of blood clotting. It is the result of a specific mutation in the gene for factor V which leads to increased risk for clots in the large veins of the legs (deep venous thrombosis), or clots that travel though the bloodstream and embed in the lungs (pulmonary embolism). It is inherited in an autosomal dominant manner. If a person inherits one copy of the mutated gene, he or she has a 2 to 8 times risk (2 to 8 in 1,000) for developing clots. If a person inherits two copies of the factor V Leiden mutation, the risk increases up to 80 times (80 in 1,000). It is estimated that three to eight per cent of the Caucasian population and 1.2 percent of the African-American population in the U.S. carry one copy of the gene and about 1 in 1000 Caucasians have two copies of the gene.


Testing: DNA analysis of the Factor V gene. Who should be tested?

  • History of venous thrombosis or pulmonary embolism, especially recurrent thrombosisHistory of transient ischemic attacks or premature strokeFamily history of thrombosisFactor V mutation in a relativeIf there is a personal or family history of clots, individuals should be tested prior to major surgery, pregnancy, postpartum, oral contraceptives or hormone replacement therapy
  • Previous finding of activated protein C analysis by laboratory analysis

Pregnancy Loss: Factor V Leiden increases the risk for recurrent fetal loss and has been associated with severe pre-eclampsia, unexplained intrauterine growth retardation, placental abruption, and stillbirth as well as maternal clotting during labor and in the postpartum period.