Factor XIII deficiency is a rare inherited bleeding disorder in which Factor XIII, the protein in the blood responsible to helping to stabilize a blood clot, is malfunctioning or deficient. If you are deficient in Factor XIII, your body is able to form blood clots, but they often are weak and therefore break down, resulting in prolonged bleeding. According to the National Organization of Rare Disorders (NORD), the incidence of factor XIII deficiency has been estimated to be between 1 in 2-5 million people in the general population. Common symptoms of factor XIII deficiency include soft tissue bleeds, intracranial bleeding, menorrhagia (heavy menstrual bleeding), and joint bleeding.