Common Types of Hemophilia

Dr. Kenneth D. Nahum, an experienced clinical researcher, has served as an investigator in more than 70 drug studies over the course of 20 years. In addition, Kenneth D. Nahum, MD, serves as an oncologist (a doctor who specializes in the diagnosis and treatment of cancer) and a hematologist (a doctor who specializes in diseases related to blood).

Hemophilia is an inherited condition in which the blood lacks the protein it needs to properly clot. Hemophilia is usually seen as one of two types: A or B.

Hemophilia A, which accounts for roughly 80 percent of all hemophilia cases, is caused by defective or missing Factor VIII, an essential blood-clotting protein. People with defective or missing Factor VIII develop mild, moderate, or severe hemophilia A. 

In most situations, hemophilia A is inherited on the X chromosome. However, the condition may develop because of a spontaneous genetic mutation, which accounts for roughly a third of all hemophilia A cases.

Meanwhile, hemophilia B is caused by a deficiency in Factor IX. In most ways, hemophilia B functions the same as hemophilia A. B is inherited on the X chromosome, but it can develop from a spontaneous mutation. Despite these similarities, the chance of developing hemophilia B is about four times lower than the chance of developing hemophilia A.