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Hemophilia B
Definition:
Hemophilia B is a hereditary blood coagulation disorder. It is caused by a deficiency of a blood plasma protein called factor IX that affects the clotting property of blood. Alternative Names:
Christmas disease; Factor IX hemophilia Text Continues Below
Causes, incidence, and risk factors:
Hemophilia is a hereditary bleeding disorder of specific blood clotting factors. There are several types of hemophilia, including hemophilia A and B. Hemophilia A is 7 times more common than hemophilia B. Hemophilia B is the result of a deficiency of clotting factor IX. The disorder is caused by an inherited X-linked recessive trait, with the defective gene located on the X chromosome. Thus, the disorder occurs primarily in males. Females carry two copies of the X chromosome, so if the factor IX gene on one chromosome is defective, the other can compensate. Males, however, carry only one X chromosome, so if the factor IX gene on that chromosome is defective, they have the disease. Females with one defective factor IX gene are carriers of this trait. Fifty percent of the male offspring of female carriers will have the disease, and 50% of their female offspring will be carriers. All female children of a male hemophiliac will be carriers of the trait.
The severity of symptoms can vary with this disease, and the severe forms become apparent early on. Bleeding is the hallmark of the disease and sometimes, though not always, occurs if an infant is circumcised. Additional bleeding manifestations make their appearance when the infant becomes mobile.
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