Hemophilia
Hemophilia, hereditary blood disease characterized by the inability of blood to clot, or coagulate, leading to hemorrhage, or excessive bleeding, even from minor injuries. The disease is caused by an insufficiency or absence of certain blood proteins, called factors, that participate in blood clotting. The most common form, hemophilia A, is observed in 80 percent of hemophiliacs and is caused by a lack of factor VIII; in the second most common, hemophilia B (Christmas disease), factor IX is missing. The severity of hemophilia varies greatly. The bleeding may occur as excessive bruising or persistent bleeding after a simple cut. Hemorrhaging into joints and muscles can be disabling. Before the advent of modern therapy, the chance of survival to adulthood was poor.
About 80 percent of all cases of hemophilia have an identifiable family history of the disease; in other instances, it may be attributable to a spontaneous mutation of genes. Researchers recently discovered that the spontaneous mutation of the factor VIII gene in two children was due to the attachment of a foreign “jumping gene” (see Genetics) that disrupted the blood-clotting ability of the factor VIII gene. Inheritance is controlled by a recessive sex-linked factor carried by the mother on the X chromosome. A probability of one in two exists that each boy born to a normal male and a carrier female will be hemophiliac and the same chance that each girl of this union will be a carrier. Of the children of a hemophiliac male and a normal female, all the girls will be carriers and all the boys will be normal. Males cannot transmit the disability, and female carriers are free of the disease.
Prevention of injury is important for the patient with hemophilia. When bleeding occurs, replacement therapy may be necessary. Freshly frozen blood plasma can be used to treat mild forms of the disease. In severe cases, hemophiliacs can administer plasma extracts at home either in a freeze-dried form that is storable for six months at room temperature or for a year in the refrigerator; or else in a form called cryoprecipitate, a concentrate that is prepared from fresh blood and must be refrigerated. Cryoprecipitate and other types of concentrates are less likely to transport diseases such as hepatitis and acquired immunodeficiency syndrome (AIDS) because concentrates are prepared from the blood of a single donor, whereas plasma comes from large pools obtained from many donors. Screening of donors and heat treatment of plasma products have recently decreased the risk of disease transmission. The cloning of factor VIII by genetic engineering allowed the development of a completely safe replacement product that was approved by the Food and Drug Administration (FDA) for commercial production in 1992. Unfortunately, a high percentage of hemophiliacs have already been exposed to the AIDS virus.
About 80 percent of all cases of hemophilia have an identifiable family history of the disease; in other instances, it may be attributable to a spontaneous mutation of genes. Researchers recently discovered that the spontaneous mutation of the factor VIII gene in two children was due to the attachment of a foreign “jumping gene” (see Genetics) that disrupted the blood-clotting ability of the factor VIII gene. Inheritance is controlled by a recessive sex-linked factor carried by the mother on the X chromosome. A probability of one in two exists that each boy born to a normal male and a carrier female will be hemophiliac and the same chance that each girl of this union will be a carrier. Of the children of a hemophiliac male and a normal female, all the girls will be carriers and all the boys will be normal. Males cannot transmit the disability, and female carriers are free of the disease.
Prevention of injury is important for the patient with hemophilia. When bleeding occurs, replacement therapy may be necessary. Freshly frozen blood plasma can be used to treat mild forms of the disease. In severe cases, hemophiliacs can administer plasma extracts at home either in a freeze-dried form that is storable for six months at room temperature or for a year in the refrigerator; or else in a form called cryoprecipitate, a concentrate that is prepared from fresh blood and must be refrigerated. Cryoprecipitate and other types of concentrates are less likely to transport diseases such as hepatitis and acquired immunodeficiency syndrome (AIDS) because concentrates are prepared from the blood of a single donor, whereas plasma comes from large pools obtained from many donors. Screening of donors and heat treatment of plasma products have recently decreased the risk of disease transmission. The cloning of factor VIII by genetic engineering allowed the development of a completely safe replacement product that was approved by the Food and Drug Administration (FDA) for commercial production in 1992. Unfortunately, a high percentage of hemophiliacs have already been exposed to the AIDS virus.
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