Factor V Leiden does not produce symptoms in most patients but can lead to blood clots, or thrombosis, which can cause pain, redness and warmth, according to Mayo Clinic. Deep vein thrombosis commonly occurs in the legs, ankles and feet and causes noticeable swelling. Clots near the skin, or superficial venous thrombosis, can cause tenderness around the area of the clot in addition to the previous symptoms.
A clot that enters the lungs, a pulmonary embolism, can lead to shortness of breath, pain when inhaling, bloody coughs and an increased heart rate, explains Mayo Clinic. Some blood clots pass without ever causing damage or producing symptoms.
A mutated F5 gene causes the condition, according to Genetics Home Reference. In addition to increasing the likelihood of blood clot formation, patients with factor V Leiden are more likely to produce clots that dislodge and move around the circulatory system. Women with the condition are at a heightened risk of multiple and late-term miscarriages. They also may be more likely to suffer from pregnancy-related complications, such as elevated blood pressure and stunted growth of the fetus, according to some research.
Patients with factor V Leiden should avoid smoking as it increases the risk of forming blood clots, states Genetics Home Reference. Old age, obesity and oral contraceptives also contribute to a heightened risk.