Hemophilia is a blood disorder that prevents blood from clotting properly, leading to uncontrolled bleeding. Hemophilia is actually a collection of several different genetic disorders passed on by heredity. The two most common types are hemophilia A and hemophilia B.

Hemophilia usually affects males. In fact, one out of every 10,000 males is born with hemophilia A. Approximately 17,000 Americans are born with the genetic disorder that causes the disease. Worldwide, an estimated 500,000 people live with some form of hemophilia.

The Hemophilias are genetic disorders caused by mutations to a single recessive gene on the X chromosome. Women with these types of genetic disorders rarely develop hemophilia, but can pass the disorders on to their sons.

Because hemophilia is an X-linked disease, the hereditary nature of the disease is a complicated issue. Further, a wide variety of genetic disorders cause hemophilia, and many mutations are only found in specific heredity groups.

Two main varieties of hemophilia exist. Hemophilia A is responsible for eighty percent of all cases. The genetic disorders responsible for hemophilia A result in low levels or abnormal production of the clotting protein factor VIII (FVIII). Hemophilia B, the second most common form of hemophilia, affects factor IX proteins (FIX) and accounts for almost twenty percent of hemophilia cases.

 

Other heredity-based hemophilia disorders may affect other blood clotting factors, but they occur rarely. The most common of these rare disorders, hemophilia C, only occurs in 1 out of every 100,000 American births. Hemophilia C affects factor XI proteins, and is unusual in that it affects both males and females.

Not all blood clotting disorders are related to hemophilia. Von Willebrand's disease, thrombocytopenia, and certain liver disorders can all interfere with blood clotting. Von Willebrand's disease is actually more common than hemophilia, and must be ruled out before a hemophilia diagnosis is made. More information on these blood disorders is available on the Coagulation Factors site.

Clotting Factors and Hemophilia Clotting factors are essential proteins found in the blood. Clotting allows blood to change from a liquid to a solid state, a protective measure that prevents excessive bleeding following injury. An absence of clotting factors results in frequent bleeding and blood loss.