An inherited bleeding disorder caused by deficiency of a blood protein, factor VIII, which is essential for blood clotting. Haemophiliacs suffer recurrent bleeding, usually into their joints, which may occur spontaneously or after injury. The lack of factor VIII is due to a defective gene, which shows a pattern of sex-linked inheritance; haemophilia affects males in most cases. Episodes of bleeding are painful and, unless treated promptly, can lead to joint deformity. Injury, and even minor operations such as tooth extraction, may lead to profuse bleeding. Internal bleeding can lead to blood in the urine or extensive bruises. Haemophilia is diagnosed by blood-clotting tests, and by amniocentesis or chorionic villus sampling in a fetus. Bleeding can be prevented or controlled by infusions of factor VIII concentrates.


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