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X-linked recessive genetic defects - how boys are affected
X-linked recessive genetic defects - how boys are affected


X-linked recessive genetic defects - how girls are affected
X-linked recessive genetic defects - how girls are affected


X-linked recessive genetic defects
X-linked recessive genetic defects


Blood cells
Blood cells


Blood clots
Blood clots


Hemophilia B

Definition:

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



Alternative Names:

Christmas disease; Factor IX hemophilia



Causes, incidence, and risk factors:

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:

  • Family history of bleeding
  • Being male


Symptoms:

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:

  • Bleeding into joints and associated pain and swelling
  • Blood in the urine or stool
  • Bruising
  • Excessive bleeding following circumcision
  • Gastrointestinal tract and urinary tract hemorrhage
  • Nosebleeds
  • Prolonged bleeding from cuts, tooth extraction, and surgery
  • Spontaneous bleeding


Signs and tests:

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:



Treatment:

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.



Support Groups:

For additional information, see hemophilia support group.



Expectations (prognosis):

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.



Complications:

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.



Calling your health care provider:

Call your health care provider if:

  • Symptoms of a bleeding disorder develop
  • A family member has been diagnosed with hemophilia B
  • If you have hemophilia B, and you plan to have children; genetic counseling is available


Prevention:

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.



References: Kessler CM. Hemorrhagic disorders: coagulation factor deficiencies. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 180.


Review Date: 3/28/2010
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; James R. Mason, MD, Oncologist, Director, Blood and Marrow Transplantation Program and Stem Cell Processing Lab, Scripps Clinic, Torrey Pines, California. 3/28/10Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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