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Definition and Epidemiology

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Hemophilia A and B are X-linked recessive inherited bleeding disorders affecting 1:5000 males with no racial predilection.1–3 Hemophilia A is caused by deficiency of factor VIII and hemophilia B is caused by deficiency of factor IX. The normal plasma levels of factor VIII or factor IX range between 50% and 150%. The severity of hemophilia is predictive of risk for bleeding and is based on plasma levels of the factor VIII or IX (Table 16-1).1

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Table Graphic Jump Location
Table 16-1. Severity of Hemophilia
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Pathogenesis

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Hemophilias are X-linked inherited bleeding disorders resulting from deficiency of clotting factors VIII or IX. Two examples of how hemophilia can be inherited are illustrated in Figures 16-1 and 16-2.2 Female carriers have adequate levels of clotting factors because of the one normal X chromosome and do not manifest the clinical disease. In a very rare circumstance, a girl may be born with hemophilia when her father has hemophilia and the mother is a carrier. Hemophilia can also occur in males who are not born to mothers who are not carriers of the abnormal gene because of mutation in the gene.

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Figure 16-1
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Mode of inheritance of hemophilia. The mother is a carrier of hemophilia. Each daughter has a 50% chance of inheriting the abnormal gene from her mother and being a carrier. Each son has a 50% chance of inheriting the abnormal gene from his mother and having hemophilia. (From:www.nhlbi.nih.gov.)

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Figure 16-2
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Mode of inheritance of hemophilia. The father has hemophilia. The mother is not a carrier of hemophilia. Each daughter will inherit the abnormal gene from her father and be a carrier. None of the sons will inherit the abnormal gene from their father, and, therefore, none will have hemophilia. (From:www.nhlbi.nih.gov.)

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Clinical Presentation

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Clinically hemophilia A and B are indistinguishable and the differentiation is based on factor assays. The clinical presentation depends upon the severity of the hemophilia. Patients with hemophilia may present with a history of easy bruising, spontaneous bleeding in the joints or muscles, and prolonged bleeding after trauma1–3 They are also at risk for intracranial bleeding and internal bleeding at various other sites such as gastrointestinal tract and kidneys. Hemophilia should be differentiated from the most common inherited bleeding disorder, von Willebrand disease resulting from von Willebrand factor abnormality. The characteristics and differences between hemophilias and von Willebrand disease are summarized in Table 16-2.1

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