Prothrombin mutation G20210A: A common genetic risk factor for thrombosis (clots) including deep venous thrombosis (DVT). It raises the risk of thrombosis significantly for both males and females in all age groups.

Prothrombin mutation G20210A gives rise to slowed mRNA degradation and to an increase in circulating prothrombin levels. This appears to create a hypercoagulable state.

The mutation is inherited in an autosomal dominant manner. If someone has the mutation, the chance is 50% that each of their sibs and children also received the mutation. Testing for prothrombin mutation G20210A is therefore useful in determining a person's predisposition to thrombosis and can assist in determining the need for anticoagulant therapy.

People who have prothrombin mutation G20210A have a 2-to-3 fold increase in the risk of DVT. Persons who have this mutation plus the Factor V Leiden mutation have a 10-to-20 fold increase in thrombotic risk. Prothrombin mutations have also been linked with thrombotic events other than DVT, including recurrent miscarriage (repeat spontaneous abortions). In addition, there may be interactions with other risk factors for thrombosis, including pregnancy, the use of oral contraceptives, and immobilization.