The best known of all the bleeding disorders is classic hemophilia (hemophilia A, the hereditary functional deficiency of factor VIII), which is the prototype of an X chromosome-linked disease, limited to males but transmitted by female carriers. Necessarily, all daughters of those with the disease are carriers, as are half the daughters of carriers. In turn, half the sons of carriers inherit the disease. A typical family history of bleeding inherited in the manner described is found in about two-thirds of cases; in the rest, the disorder appears to arise de novo, either because a fresh mutation has occurred or because cases were unrecognized in earlier generations.
Classic hemophilia varies in severity from family to family. In the most severe cases, in which plasma is essentially devoid of factor VIII, the patients may bruise readily and bleed apparently spontaneously into soft tissues and joints, with the latter resulting in crippling joint disease. Trauma, surgical procedures, and dental extractions may lead to lethal bleeding. The life expectancy of those with severe classic hemophilia is foreshortened, death coming from exsanguination, bleeding into a vital area, or infection. The prognosis of classic hemophilia has been greatly improved by modern therapy in which episodes of bleeding are controlled by transfusion of fractions of normal plasma containing the functionally missing proteins. This therapy is not without hazard, for transfusion of concentrates of factor VIII derived from normal plasma has been complicated by transmission of the viruses of hepatitis and the acquired immune deficiency syndrome (AIDS).
In those families in which classic hemophilia is milder, bleeding occurs only after injury, surgery, or dental extraction. The severity of clinical symptoms is paralleled by the degree of the deficiency of antihemophilic factor (factor VIII), as measured in tests of its coagulant function.
Classic hemophilia appears to be distributed worldwide, but geographic differences in incidence have been described. Whether classic hemophilia is less prevalent in blacks than in other groups, as has been suggested, is uncertain.
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