What Is Hemophilia?
Hemophilia (heem-o-FILL-ee-ah) is a rare bleeding disorder in which the blood doesn't clot normally. If you have hemophilia, you may bleed for a longer time than others after an injury. You also may bleed inside your body (internally), especially in your knees, ankles, and elbows. This bleeding can damage your organs and tissues and may be life threatening. Overview
Hemophilia usually is inherited. "Inherited” means that the disorder is passed from parents to children through genes. People born with hemophilia have little or no clotting factor. Clotting factor is a protein needed for normal blood clotting. There are several types of clotting factors. These proteins work with platelets (PLATE-lets) to help the blood clot. Platelets are small blood cell fragments that form in the bone marrow—a sponge-like tissue in the bones. Platelets play a major role in blood clotting. When blood vessels are injured, clotting factors help platelets stick together to plug cuts and breaks on the vessels and stop bleeding. The two main types of hemophilia are A and B. If you have hemophilia A, you're missing or have low levels of clotting factor VIII (8). About 8 out of 10 people who have hemophilia have type A. If you have hemophilia B, you're missing or have low levels of clotting factor IX (9). Rarely, hemophilia can be acquired. "Acquired” means you aren't born with the disorder, but you develop it during your lifetime. This can happen if your body forms antibodies (proteins) that attack the clotting factors in your bloodstream. The antibodies can prevent the clotting factors from working. This article focuses on inherited hemophilia.
Hemophilia can be mild, moderate, or severe, depending on how much clotting factor is in your blood. About 7 out of 10 people who have hemophilia A have the severe form of the disorder. People who don't have hemophilia have a factor VIII activity of 100 percent. People who have severe hemophilia A have a factor VIII activity of less than 1 percent.
He mophilia usually occurs in males (with rare exceptions). About 1 in 5,000 males are born with hemophilia each year.
Other Names for Hemophilia
Factor VIII deficiency
Factor IX deficiency
What Causes Hemophilia?
If you have inherited hemophilia, you're born with the disorder. It's caused by a defect in one of the genes that determine how the body makes blood clotting factor VIII or IX. These genes are located on the X chromosomes (KRO-muh-somz). Chromosomes come in pairs. Females have two X chromosomes, while males have one X and one Y chromosome. Only the X chromosome carries the genes related to clotting factors. A male who has a faulty hemophilia gene on his X chromosome will have hemophilia. A female must have the faulty gene on both of her X chromosomes to have hemophilia, which is very rare. If a female has the faulty gene on only one of her X chromosomes, she is a "hemophilia carrier.” Carriers don't have hemophilia, but they can pass the faulty gene to their children. Below are two examples of how the hemophilia gene is inherited. Inheritance Pattern for Hemophilia—Example 1
The image shows one example of how the hemophilia gene is inherited. In this example, the father doesn't have hemophilia (that is, he has two normal chromosomes—X and Y). The mother is a carrier of hemophilia (that is, she has one faulty X chromosome and one normal X chromosome). Each daughter has a 50 percent chance of inheriting the faulty gene from her mother and being a carrier. Each son has a 50 percent chance of inheriting the faulty gene from his mother and having hemophilia. Inheritance Pattern for Hemophilia—Example 2
The image shows one example of how the hemophilia gene is inherited. In this example, the father has hemophilia (that is, his X chromosome is faulty). The mother isn't a hemophilia carrier (that is, she has two normal X chromosomes). Each...
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