Haemophilia B is a bleeding disorder that slows the blood clotting process. People with this disorder experience prolonged bleeding or oozing following an injury or surgery. In severe cases of hemophilia, heavy bleeding occurs after minor injury or even in the absence of injury. Serious complications can result from bleeding into the joints, muscles, brain, or other internal organs. Milder forms may not become apparent until abnormal bleeding occurs following surgery or a serious injury. Hemophilia B is caused by mutations in the F9 gene which encodes coagulation factor IX.
Hemophilia primarily affects males, but a milder, symptomatic form of hemophilia B in female carriers has also been described.