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The Defect In Hemophilia

In hemophilia, certain clotting factors are either decreased in quantity, absent, or improperly formed. Because the clotting cascade uses amplification to rapidly plug up a bleeding area, absence or inactivity of just one clotting factor can greatly increase bleeding time.

Hemophilia A is the most common type of bleeding disorder, and involves decreased activity of factor VIII. Three levels of factor VIII deficiency exist, and are classified based on the percentage of normal factor VIII activity present. Half of all people with hemophilia A have severe hemophilia. This means that their factor VIII activity level is less than 1% of the normal level. Such individuals frequently experience spontaneous bleeding, most frequently into their joints, skin, and muscles. Surgery or trauma can result in life-threatening hemorrhage, and must be carefully managed. Individuals with 1-5% of normal factor VIII activity level have moderate hemophilia, and are at risk for heavy bleeding after seemingly minor traumatic injury. Individuals with 5-40% of normal factor VIII activity level have mild hemophilia, and must prepare carefully for any surgery or dental procedures.

Individuals with hemophilia B have very similar symptoms, but the deficient factor is factor IX. Hemophilia C is very rare, and much more mild than hemophilias A or B; it involves factor XI.

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Science EncyclopediaScience & Philosophy: Habit memory: to HeterodontHemophilia - Normal Blood Clotting, The Defect In Hemophilia, How Hemophilia Is Inherited, Symptoms Of Hemophilia - Diagnosis