The factor V Leiden mutation does not itself cause any symptoms. Since factor V Leiden is a risk for developing blood clots in the leg or lungs, the first indication that you have the disorder may be the development of an abnormal blood clot. Some clots do no damage and disappear on their own. Others can be life-threatening. Symptoms of a blood clot depend on what part of your body is affected. A clot in a deep vein This is known as deep vein thrombosis (DVT), which most commonly occurs in the legs. A DVT may not cause any symptoms. If signs and symptoms do occur, they can include: 
Pain
Swelling
Redness
Warmth
 A clot that travels to your lungs Known as a pulmonary embolism, this occurs when a portion of a DVT breaks free and travels through the right side of your heart to your lung, where it blocks blood flow. This can be a life-threatening situation. Signs and symptoms may include: 
Sudden shortness of breath
Chest pain when breathing in
A cough that produces bloody or blood-streaked sputum
Rapid heartbeat
