In 1994 factor V Leiden, resistant to inactivation by protein C, was described; this abnormality is the most common genetic cause for thrombosis.

In North American and European populations, around 4-8% of people have a thrombophilia, most commonly factor V leiden and prothrombin G20210A.

Most cases of venous thrombosis are due to acquired states (older age, surgery, cancer, immobility) or inherited thrombophilias (e.g., antiphospholipid syndrome, factor V Leiden, and various other genetic deficiencies or variants).

Determination of the Factor V Leiden Mutation Two-milliliter samples of whole blood were collected in buffered sodium citrate, and high molecular weight genomic DNA was obtained from the peripheral blood leukocyte fraction (QIAamp Blood Tissue Kit, Qiagen, Valencia CA).