Genetics
Clotting factor II, or prothrombin, located on chromosome 11, is a vitamin K–dependent proenzyme that functions in the blood coagulation cascade.  Factor II deficiency is a rare, inherited or acquired bleeding disorder.  The prothrombin G20210A mutation alters the polyadenylation site of the gene and results in increased mRNA synthesis with a subsequent increase in protein expression.  This mutation results in increased levels of plasma prothrombin and a concurrent increased risk for the development of thrombosis and hypercoagulability which may contribute to infertility.

Incidence

• The prothrombin mutation is seen in approximately 6–7% of thrombosis patients and 1–2% of healthy individuals
• The gene may be inherited heterozygous, or much more rarely, homozygous (1 in 10,000), and is not related to gender or blood type
• The mutation is uncommon in African Americans (approximately 0.5%) and is rare in Asians, Africans, and Native Americans, and seen in 2% of Caucasian US population

Symptoms/Characteristics

• Deep vein thrombosis (DVT)
• A pulmonary embolism (PE) or a blood clot in an unusual site (such as the mesenteric or cerebral sinus vein)
• A heart attack or stroke at a young age
• A history of recurrent pregnancy loss or stillbirth

Clinical Management

Anticoagulants are often prescribed to individuals with Factor II Mutation.
Having a DVT and PE in the past increases your risk of developing another one in the future; however, having the prothrombin mutation does not increase the risk of future blood clots.  This reflects the fact that the prothrombin mutation is not a very strong risk factor for blood clots.  Patients who have not had a blood clot in the past should not be routinely treated with blood thinning medication.  Instead, they should be counseled about reducing or eliminating other risk factors.