What Is Hemophilia?
Hemophilia is a medical condition that limits the blood’s ability to clot. It’s almost always inherited and more commonly affects males.
Normally, bleeding stops when blood clots form. This response depends on the combined action of proteins called clotting factors and platelets, a type of blood cell.
In people with hemophilia, the body doesn’t produce enough of a particular clotting factor or makes ineffective factor. The severity of hemophilia symptoms depends on how much clotting factor your body produces. Some people with hemophilia have enough clotting factor to keep symptoms mild. They only need to take occasional precautions. People with lower clotting factor levels experience more severe disease.
Thanks to advances in hemophilia therapies, people with the condition can live full lives — even with severe disease. Researchers are also working on potential cures for hemophilia.
Learn more about bleeding disorders treatment at Penn Medicine and our comprehensive hemophilia treatment center.
What Causes Hemophilia?
In most cases, hemophilia is inherited, resulting from changes to certain genes that control clotting factor production. The genes responsible — and the clotting factors they’re associated with — determine the type of hemophilia.
In rare cases, hemophilia is acquired, meaning people are not born with it. In these cases, hemophilia results from damage to clotting factor by immune system proteins. This type of hemophilia can occur during or immediately after pregnancy or when you have an autoimmune disorder and grow older. Sometimes the cause of acquired hemophilia is not known.
Hemophilia A and Clotting Factor VIII
Hemophilia A, also called classic hemophilia, is the most common form. It’s caused by changes to the F8 gene, which controls clotting factor VIII.
Because the F8 gene sits on the X chromosome, severe disease typically gets passed down only to male children, who have only one X chromosome. Even then, just because a parent has hemophilia doesn’t mean it will automatically get passed on.
Females have two X chromosomes. If one has the F8 change that causes hemophilia, the other can still make normal clotting factor VIII. For a female child to inherit severe disease, both parents must have hemophilia, a very rare circumstance. However, females with one copy of the hemophilia A variant may still have symptoms and clotting factor low enough to be diagnosed with mild forms of hemophilia.
Women who have one copy of the factor VIII variant are called carriers; they can still pass the genetic change on to their children.
Hemophilia B and Clotting Factor IX
Hemophilia B is sometimes called Christmas disease, after the last name of the first child diagnosed with this condition. It’s caused by changes to the F9 gene, responsible for clotting factor IX.
Hemophilia B follows the same inheritance patterns as hemophilia A.
Hemophilia C and Clotting Factor XI
Hemophilia C is rarer than hemophilia A or B. It’s caused by changes to the F11 gene, which controls clotting factor XI.
Hemophilia C varies in other ways, too. Because the gene sits on a different chromosome, the condition gets passed down to both male and female children. For most patients, symptoms are mild.
Hemophilia Symptoms
People with hemophilia have increased bleeding. The frequency and circumstances of bleeding depend on how severe hemophilia is:
- Mild hemophilia: People with mild hemophilia may only experience prolonged bleeding with medical or dental procedures or serious injuries. Heavier bleeding may also be experienced during menstruation or delivery. Doctors help people plan ahead for these events when possible and take preventive steps. Learn more about our evaluations of heavy periods.
- Severe hemophilia: People with severe hemophilia bleed more easily from injuries. They may also bleed for no apparent reason, a situation called spontaneous bleeding. Bleeding inside the body can damage muscles and joints, especially the ankles, knees, and elbows. The joints may develop a severe form of arthritis called hemophilic arthropathy. Internal bleeding can also harm organs, including the brain. Fortunately, people can now take effective, ongoing treatment to prevent these complications.
How Is Hemophilia Diagnosed?
Some families already know they have a history of hemophilia, so children get diagnosed right away. Otherwise, severe hemophilia typically gets noticed in early childhood when it causes symptoms.
With mild hemophilia, age at diagnosis varies. An older girl may get diagnosed after menstruation begins, for example. Others are diagnosed after injuries that cause bleeding or when blood tests done for unrelated reasons show clotting factor changes. Sometimes mild hemophilia is not discovered until adulthood.
Tests for hemophilia look at the blood’s ability to clot and how long the process takes, as well as the amount of particular clotting factors. Genetic testing can look for the inherited change responsible.
Hemophilia Treatment
With mild or moderate inherited hemophilia, you may only need treatment in special situations, such as before surgery or labor. More severe inherited hemophilia often requires ongoing treatment.
Medications called factor replacements provide the missing clotting factor and promote clotting. Non-factor replacements work to prevent or stop bleeding.
Researchers are also working on ways to restore the genetic information needed to produce the missing clotting factor. The Food and Drug Administration has approved a gene therapy for hemophilia B, with additional clinical trials underway for both hemophilia A and B. Gene therapy can potentially remove the need for frequent treatment.
For acquired hemophilia, doctors typically prescribe therapy that suppresses, or holds back, the immune system.
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