Hemophilia A is characterized by deficiency in factor VIII clotting activity that results in prolonged bleeding after injuries, tooth extractions, or surgery, and delayed or recurrent bleeding prior to complete wound healing. The age of diagnosis and frequency of bleeding episodes are related to the level of factor VIII clotting activity. Individuals with severe hemophilia A are usually diagnosed during the first two years of life following oral or soft tissue bleeding either with procedures or due to a known family history of hemophilia. Without prophylactic treatment, individuals may average up to two to five spontaneous bleeding episodes each month including spontaneous joint bleeds or deep-muscle hematomas, and prolonged bleeding or excessive pain and swelling from minor injuries, surgery, and tooth extractions. Individuals with moderate hemophilia A seldom have spontaneous bleeding, although it varies between individuals; however, they do have prolonged or delayed bleeding after relatively minor trauma and are usually diagnosed before age five to six years; the frequency of bleeding episodes varies, usually from once a month to once a year. Individuals with mild hemophilia A do not have spontaneous bleeding episodes; however, without pre- and postoperative treatment, abnormal bleeding occurs with surgery or tooth extractions; the frequency of bleeding episodes varies widely, typically from once a year to once every ten years. Individuals with mild hemophilia A are often not diagnosed until later in life. Approximately 30% of heterozygous females have factor VIII clotting activity below 40% and are at risk for bleeding (even if males in the family are only mildly affected). After major trauma or invasive procedures, prolonged or excessive bleeding usually occurs, regardless of severity. In addition, 25% of heterozygous females with normal factor VIII clotting activity report an increased bleeding tendency. [from GeneReviews]