Hemophilia can vary in its severity, depending upon the particular type of mutation (genetic defect). The degree of symptoms depends upon the levels of the affected clotting factor. Severe disease is defined as <1% factor activity, 1% to 5% factor activity is moderate disease, and greater than 5% factor activity constitutes mild disease. The extent of bleeding is dependent upon the severity (the amount of factor activity) and is similar for hemophilia A and B.
With severe hemophilia (A or B), bleeding begins at an early age and may occur spontaneously. Those with mild hemophilia may only bleed excessively in response to injury or trauma. Female carriers of hemophilia have variable degrees of factor activity; some may have near normal levels and do not show any bleeding tendencies, while some may have less than the predicted 50% reduction and may bleed more often than non-carrier females.
In severe hemophilia, bleeding episodes usually begin within the first 2 years of life. Heavy bleeding after circumcision in males is sometimes the first sign of the condition. Symptoms may develop later in those with moderate or mild disease. The bleeding of hemophilia can occur anywhere in the body. Common sites for bleeding are the joints, muscles, and gastrointestinal tract. Specific sites and types of bleeding are discussed below.