Factor XIII deficiency is a rare hereditary coagulation disorder in which factor XIII, the protein in the blood that stabilises clots, is missing or not working properly. If you have a factor XIII deficiency, your body can still form blood clots but they tend to be weak and break up easily, which results in prolonged bleeding. Common symptoms of factor XIII deficiency include bleeding into the soft tissues, bleeding into the brain, prolonged menstrual periods, and bleeding into the joints.