Definition of Hemophilia B:

Hemophilia B is a hereditary blood coagulation disorder. It is caused by a deficiency of a blood plasma protein called factor IX. Without enough factor IX, the blood cannot clot properly to control bleeding.

Causes, incidence, and risk factors:

Hemophilia is a hereditary bleeding disorder of specific blood clotting factors. There are several types of hemophilia, including hemophilia A and B. Hemophilia A is 7 times more common than hemophilia B. Hemophilia B is the result of a deficiency of clotting factor IX.

The disorder is caused by an inherited X-linked recessive trait, with the defective gene located on the X chromosome. Females have two copies of the X chromosome, so if the factor IX gene on one chromosome is defective, the other can compensate. Males, however, have only one X chromosome, so if the factor IX gene on that chromosome is defective, they will have the disease. Thus, more males than females have hemophilia.

Females with one defective factor IX gene are carriers of (they don't have symptoms). In women who are carriers, their male babies have a 50% chance of having the disease, while their female babies have a 50% chance of being a carrier.

The severity of symptoms can vary, and the severe forms become apparent early on. Bleeding is the main symptom of the disease and sometimes, though not always, occurs if an infant is circumcised. Additional bleeding problems usually show up when the infant becomes mobile.

Mild cases may go unnoticed until later in life, when they occur in response to surgery or trauma. Internal bleeding may occur anywhere and bleeding into joints is common. Risk factors are a family history of bleeding and being male.