"Haemophilia may be a mostly inherited genetic disease that impairs the body's ability to form blood clots, a process needed to prevent bleeding. This results in people bleeding for a longer time after an injury, easy bruising, and an increased risk of bleeding inside joints or the brain. Those with a light case of the disease may have symptoms only after an accident or during surgery. Bleeding into a joint may result in permanent damage while bleeding within the brain may result in future headaches, seizures, or a decreased level of consciousness.
There are two main types of haemophilia: haemophilia A, which occurs due to low amounts of clotting factor VIII, and haemophilia B, which occurs due to low levels of clotting factor IX. They are typically inherited from one's parents through an X chromosome carrying a nonfunctional gene. Rarely a replacement mutation may occur during early development or haemophilia may develop later in life thanks to antibodies forming against a coagulation factor."