Hemophilia refers to a group of clotting factor deficiencies. Hemophilia is probably the most well-known of the coagulopathies. Patients with hemophilia will experience prolonged bleeding following an injury or surgery. Since hemophilia is the result of a clotting factor deficiency, the severity of hemophilia can vary significantly depending on the degree to which the factor is decreased. In mild cases, only minor bruising or a slight prolongation in the bleeding time may be observed. But in severe cases of hemophilia, continuous bleeding can occur with injury or even in the absence of injury (e.g., spontaneous nose or gum bleeding). Serious complications can result when internal bleeding happens. Bleeding into organs, joint spaces, or the brain can lead to severe morbidity or mortality if not corrected.
There are two primary hemophilias—hemophilia A and hemophilia B. Von Willebrand's disease is sometimes grouped with hemophilia since it too can be caused by a factor deficiency. But von Willebrand's disease is more complex and usually milder than hemophilia. We will consider it in a separate section. There is a condition referred to as hemophilia C which involves a deficiency of clotting factor XI. This condition is rarer than hemophilia A and B and has milder symptoms.
Hemophilia is an inherited condition caused by a mutation on the X chromosome. Since males only have one X chromosome, they are at higher risk for hemophilia since it only takes one altered copy of the gene to cause the condition. Females have two X chromosomes, so a mutation would have to be present in both copies of the gene for a clinically significant condition to occur. Because it is less likely that females will have two altered copies of this gene, it is rare for females to have hemophilia. Also, note that an X-linked condition means that fathers cannot pass the trait on to their sons.
In X-linked recessive inheritance, a female with one altered copy of the gene is called a carrier. Hemophilia carrier females have about half the usual amount of coagulation factor VIII or coagulation factor IX. This is usually enough for normal coagulation. A female who is a carrier has a 50 percent chance of passing on her X chromosome with the gene mutation for hemophilia A or B to their son.
