What is hemophilia?
Hemophilia is a rare and serious X-chromosome linked congenital bleeding disorder that affects the blood's ability to clot, meaning that people with hemophilia bleed for a longer time than normal.
To understand hemophilia, it is helpful to know how the body normally works when it comes to stopping a bleed. When a person bleeds, 13 different proteins—called clotting factors—work together to form a blood clot.
In people living with hemophilia, one of the clotting factors is missing or reduced, which prevents this process from working. They have trouble forming blood clots—so it’s harder to stop bleeds when they happen.
People living with hemophilia are typically born with it. In the majority of these cases, it is passed to a child from the mother's side of the family. Sometimes, a person may develop hemophilia without any family history. In fact, nearly one-third of hemophilia cases are not inherited and have no family history of the disease. Since the genes for coagulation factors are on the X chromosome, hemophilia mainly affects males who inherit an affected maternal X chromosome.
Due to a lack of bleeding at birth or because the family doesn't have a history of hemophilia, some people who have hemophilia are not diagnosed as newborns.
of people with hemophilia have hemophilia A. Also known as factor VIII (8) deficiency, it is caused by a lack of the clotting factor known as factor VIII.
of people with hemophilia have hemophilia B. Also called factor IX (9) deficiency, it’s caused by a lack of—you guessed it—factor IX.
Hemophilia A affects 1 in 5000 male births in the United States.