Factor V Leiden is a gene mutation that causes a blood clotting disorder. It makes those affected more likely to develop dangerous blood clots, known as deep vein thrombosis or pulmonary embolisms. Testing can identify if someone carries the Factor V Leiden gene mutation. Treatment may include blood thinners to prevent clotting if high risk situations like surgery or pregnancy occur. Lifestyle changes like staying active and avoiding prolonged immobility can also help reduce risks.