Hemophilia is the most common hereditary blood disorder, affecting approximately one in ten thousand people, almost all male. People with hemophilia suffer from abnormal blood clotting. In normal blood, proteins called clotting factors work together to form a clot whenever bleeding occurs. The person with hemophilia lacks or doesn't have enough of a certain clotting factor so the blood can't make a clot.
The most common form, hemophilia A, is observed in 80 percent of hemophiliacs and is caused by a lack of factor VIII, and in the second most common, hemophilia B, factor IX is missing. Hemophilia is classified as either mild, moderate or severe, depending on the amount of clotting factor a person has in his body. Severe hemophilia is suprisingly the most common form. A person with severe hemophilia has less than 1% of the normal amount of clotting factor in their body. .
A person with mild hemophilia may only have problems with bleeding when he has surgery, severe dental work, or a major injury. A person with moderate hemophilia will have those problems plus bleeding problems with more minor injuries such as a hard bump to the elbow. Lastly, a person with severe hemophilia can have what are called spontaneous bleeds. Which is bleeding that starts inside the body for no known reason. The following diagram illustrates the levels of clotting factor found in normal people, as well as people with mild to moderate to severe hemophilia.
A very large percent of all cases of hemophilia have an identifiable family history of the disease. Inheritance is controlled by a recessive sex-linked factor carried by the mother on the X chromosome. .
Currently, most people with severe forms of hemophilia use a prophylactic treatment in which they infuse, the needed factor proteins into their bloodstream through a vein or through a closed tube leading into a vein. This treatment is called "factor replacement therapy".