Hemophilia B is a hereditary bleeding disorder caused by a lack of blood clotting factor IX. Without enough factor IX, the blood cannot clot properly to control bleeding.
See also: Coagulation disorder
Hemophilia B 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 gene on the other chromosome can do the job of making enough factor IX.
Males, however, have only one X chromosome, so if the factor IX gene on that chromosome is defective, they will have Hemophilia B. Therefore, most people with hemophilia B are male.
If a woman has a defective factor IX gene, she is considered a carrier. This means the defective gene can be passed down to her children.
Boys born to a woman who carries the defective gene have a 50% chance of having hemophilia B, while their daughters have a 50% chance of being a carrier.
All female children of men with hemophilia carry the defective gene.
Risk factors for hemophilia B include:
The severity of symptoms can vary, and the severe forms become apparent early on.
Bleeding is the main symptom of the disease and sometimes, although 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.
Symptoms can include:
If the patient is the first person in the family to have a suspected bleeding disorder, he or she will undergo a series of tests called a coagulation study. Once the specific defect has been identified, other family members will need less testing to diagnose the disorder.
Tests results may include:
Standard treatment is infusion of factor IX concentrates to replace the defective clotting factor. The amount infused depends upon the severity of bleeding, the site of the bleeding, and the size of the patient.
To prevent a bleeding crisis, people with hemophilia and their families can be taught to administer factor IX concentrates at home at the first signs of bleeding. People with severe forms of the disease may need ongoing, preventive infusions.
Depending on the severity of the disease, factor IX concentrate may be given prior to dental extractions and surgery to prevent bleeding.
Hepatitis B vaccine is recommended for individuals with hemophilia B because they are at increased risk of developing hepatitis due to exposure to blood products.
For additional information, see hemophilia support group.
The outcome is usually good with treatment. Most people with hemophilia are able to lead relatively normal lives. A small number of people develop inhibitors of factor IX, and may die from loss of blood.
Patients with hemophilia B should establish regular care with a hematologist, especially one who is associated with a hemophilia treatment center. The ability to have quick and easy access to medical records documenting the patient's history of factor IX levels, factor transfusions (including the type and amount), complications, and amount of any inhibitors can be lifesaving in the event of an emergency situation.
Chronic joint deformities may occur from recurrent bleeding into the joint. These can be managed by an orthopedic specialist. However, joint replacement(s) may be needed.
Intracerebral hemorrhage (such as deep intracerebral hemorrhage and lobar intracerebral hemorrhage) may also occur.
Repeated transfusions may slightly raise the risk for HIV and hepatitis, however, continued improvements in blood screening procedures makes blood products safer than ever.
Thrombosis may occur following use of factor IX concentrate.
Call your health care provider if:
Genetic counseling may be recommended. Testing can identify females who carry the hemophilia gene. Prenatal intrauterine tests can be done to determine if a developing baby has the disorder.
Christmas disease; Factor IX hemophilia