Taking Advantage of Genetic Knowledge

Taking Advantage of Genetic Knowledge

Men and women who have family members with hemophilia often have genetic counseling and testing to find out what their chances are to pass on the disease to another generation. In addition, the testing may uncover important and specific information about a patient's disease and the best ways to treat it.

Hemophilia is caused by a mutation (alteration) of a gene on the X chromosome. Males have only one X chromosome, so a single altered copy of one of these genes is enough to cause hemophilia. Females, on the other hand, carry two X chromosomes, so they need a mutation in both copies of the gene—one inherited from their mother and the other from their father—to develop the disease. Consequently, hemophilia is very rare in girls and women.

People with hemophilia A are born with a mutation of the F8 gene that causes them to have less factor VIII in their blood than they should. Likewise, those with hemophilia B are born with a mutation of the F9 gene that causes them to have too little factor IX. The deficiency in factor VIII or IX results in bleeding, the severity of which depends on how much of these clotting factors is missing.

Genetics can help doctors treat hemophilia and affect how well an individual will respond to hemophilia treatment. In a study of 621 persons with hemophilia who had not yet started treatment, persons with a particular type of mutation experienced bleeding into the joints 2 months before those having another type of mutation. Another study analyzed the genetic information of people with severe hemophilia B to find out what factors increased their risk of having a rare, severe allergic reaction (anaphylaxis) to FIX replacement therapy. Those who had particular genetic mutations had the greatest risk of experiencing anaphylaxis during treatment.

What Does This Mean to People With Hemophilia?

Hemophilia is a genetic disease, and information about genes and any mutations present provides a wealth of information that can help shape the course of treatment for individual patients. Right now, a special committee of the National Hemophilia Foundation recommends that all persons with hemophilia have genotype testing. This genetic information is being entered into a database to further study of the disease. In addition, family members of these individuals also may be tested to find out if they are carriers of the disease and to provide counseling if they are. In the future, mapping of genetic information may help doctors design personalized treatment programs for patients with hemophilia.

About 45% of people with hemophilia A have a specific gene alteration known as an inversion 22 mutation. Patients with severe hemophilia A are screened for the presence of this mutation. If the results of this screening are negative, they then should receive genetic testing. All patients with hemophilia B should be tested genetically.

Women who are carriers of the disease—based on a history of hemophilia in their family—but have no symptoms also should undergo genetic testing. If carrier status is confirmed, these women can be counseled about family planning options. When such women become pregnant with a male fetus, they are followed by a team of specialists throughout their pregnancy to make sure that their baby is delivered safely.

Further information about genetic testing for hemophilia and related subjects may be found by visiting the websites listed in the chart below.

Resources for Hemophilia Information and Genetic Testing

Gene Review: Hemophilia A
http://www.ncbi.nlm.nih.gov/books/NBK1404/

Gene Review: Hemophilia B
http://www.ncbi.nlm.nih.gov/books/NBK1495/

Genetic Testing Registry: Hemophilia
http://www.ncbi.nlm.nih.gov/gtr/conditions/C0684275/

Genetic Testing Registry: Hemophilia B(M)
http://www.ncbi.nlm.nih.gov/gtr/conditions/CN043453/

Genetic Testing Registry: Hereditary Factor IX Deficiency Disease
http://www.ncbi.nlm.nih.gov/gtr/conditions/C0008533/

Genetic Testing Registry: Hereditary Factor VIII Deficiency Disease
http://www.ncbi.nlm.nih.gov/gtr/conditions/C0019069/

Lab Tests Online: Bleeding Disorders
http://labtestsonline.org/understanding/conditions/bleeding-disorders

MedlinePlus Encyclopedia: Factor IX Assay
http://www.nlm.nih.gov/medlineplus/ency/article/003679.htm

MedlinePlus Encyclopedia: Factor VIII Assay
http://www.nlm.nih.gov/medlineplus/ency/article/003678.htm

MedlinePlus Encyclopedia: Hemophilia A
http://www.nlm.nih.gov/medlineplus/ency/article/000538.htm

MedlinePlus Encyclopedia Hemophilia B
http://www.nlm.nih.gov/medlineplus/ency/article/000539.htm

National Heart, Lung, and Blood Institute: How is Hemophilia Diagnosed?
http://www.nhlbi.nih.gov/health/health-topics/topics/hemophilia/diagnosis.html

National Heart, Lung, and Blood Institute: How is Hemophilia Treated?
http://www.nhlbi.nih.gov/health/health-topics/topics/hemophilia/treatment.html

National Hemophilia Foundation: Hemophilia Treatment Centers
http://www.hemophilia.org/NHFWeb/MainPgs/MainNHF.aspx?menuid=203&contentid=385

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