Factor X deficiency (also known as Stuart-Prower deficiency) is a rare bleeding disorder caused by the absence or low levels of a specific clotting protein in the blood, called “factor X.” Factor X deficiency affects males and females equally. Symptoms can be mild, moderate or severe depending on the level of circulating factor X in the bloodstream. Common symptoms include easy bruising, frequent nosebleeds, bleeding gums, blood in the urine, and prolonged bleeding after minor injuries. Women with Factor X deficiency may also experience heavy menstrual bleeding and may have an increased risk for first trimester miscarriages. Acquired (non-inherited) Factor X deficiency is the most common form of the disorder. Acquired Factor X deficiency can be caused by liver disease, vitamin K deficiency, exposure to certain medications that affect clotting, and certain types of cancer.