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Causes
By Mayo Clinic staffCoagulation involves blood particles called platelets and procoagulant plasma proteins called clotting factors. The cause of hemophilia is a deficiency of one of these clotting factors. Which type of hemophilia you have depends on which clotting factor is deficient:
- Hemophilia A. The most common type, hemophilia A is caused by lack of enough clotting factor VIII.
- Hemophilia B. This second most common type is caused by lack of enough clotting factor IX.
- Hemophilia C. This type is rare in the United States, and it has a different inheritance pattern. Its cause is a lack of clotting factor XI, and symptoms are generally mild with this type of hemophilia.
The coagulation process
Coagulation begins when platelets stick to a blood vessel at the site of an injury. A cascade of enzyme reactions occurs to produce a web-like protein network that encircles the platelets and holds them in place (platelet phase) to form a clot (coagulation phase). In this cascade, each clotting factor is transformed, in turn, from an inactive to an active form.
Three categories of blood proteins play a role in this process:
- Procoagulant proteins. These proteins help form clots.
- Anticoagulant proteins. These proteins prevent formation of clots.
- Fibrinolytic proteins. These proteins help dissolve clots that have formed.
Hemophilia inheritance
Everyone has two sex chromosomes, one from each parent. Females inherit an X chromosome from their mother and an X chromosome from their father. Males inherit an X chromosome from their mother and a Y chromosome from their father.
- The gene that causes hemophilia A or B is located on the X chromosome, so it can't be passed from father to son. Hemophilia A or B almost always occurs in boys, and is passed from mother to son through one of the mother's genes. Most women who have the defective gene are simply carriers and exhibit no signs or symptoms of hemophilia. It's also possible for hemophilia A or B to occur through spontaneous gene mutation.
- The gene that causes hemophilia C can be passed on to children by either parent. Hemophilia C can occur in both boys and girls.
- Ferri FF. Hemophilia. In: Ferri FF. Ferri's Clinical Advisor 2009. St. Louis, Mo.: Mosby; 2008. http://www.mdconsult.com/das/book/body/127220953-8/819378765/1701/258.html#4-u1.0-B978-0-323-04134-8..50011-2--subchapter13_5514. Accessed March 21, 2009.
- Hoots KW, et al. Clinical manifestations and diagnosis of hemophilia. http://www.uptodate.com/home/index.html. Accessed March 21, 2009.
- Hemophilia. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/hemophilia/hemophilia_what.html. Accessed March 21, 2009.
- Hemophilia. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/sec11/ch136/ch136d.html. Accessed March 21, 2009.
- Hoots KW, et al. Treatment of hemophilia. http://www.uptodate.com/home/index.html. Accessed March 21, 2009.
- Kessler CM. Hemorrhagic disorders: Coagulation factor deficiencies. In: Goldman L, et al., eds. Cecil Medicine. 23rd ed. Philadelphia, Pa.: Saunders Elsevier; 2007:697.
- Pruthi RK (expert opinion). Mayo Clinic, Rochester, Minn. April 9, 2009.
