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Hemophilia
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Hemophilia

Hemophilia is a bleeding disorder that slows the blood clotting process, often resulting in prolonged bleeding or oozing following injury, surgery, or medical procedures.

Overview

People with this condition experience prolonged bleeding or oozing following an injury, surgery, or having a tooth pulled. In severe cases, continuous bleeding occurs after minor trauma or even when there is no obvious injury, which is sometimes called spontaneous bleeding. Serious complications can result from bleeding into the joints, muscles, brain, or other internal organs. Milder forms of hemophilia do not necessarily involve spontaneous bleeding, and the condition may not become apparent until abnormal bleeding occurs following surgery or a serious injury.

The major types of this condition are hemophilia A (also known as classic hemophilia or factor VIII deficiency) and hemophilia B (also known as Christmas disease or factor IX deficiency). Although the two types have very similar signs and symptoms, they are caused by variants in different genes. People with an unusual form of hemophilia B, known as hemophilia B Leyden, experience episodes of excessive bleeding in childhood but have few bleeding problems after puberty.

Frequency

The two major forms of hemophilia occur much more commonly in males than in females. Hemophilia A is the most common type of the condition; 1 in 4,000 to 1 in 5,000 males worldwide are born with this disorder. Hemophilia B occurs in approximately 1 in 20,000 newborn males worldwide.

Causes

Variants in the F8 gene cause hemophilia A, while variants in the F9 gene cause hemophilia B. The F8 gene provides instructions for making a protein called coagulation factor VIII. A related protein, coagulation factor IX, is produced from the F9 gene. Coagulation factors are proteins that work together in the blood clotting process. After an injury, blood clots protect the body by sealing off damaged blood vessels and preventing excessive blood loss.

  • Genetic Variants: Variants in the F8 or F9 gene lead to the production of an abnormal version of these proteins or reduce the amount produced. As a result, blood clots cannot form properly.
  • Severity: Variants that cause severe hemophilia almost completely eliminate the activity of the coagulation factor. Variants involved in mild and moderate hemophilia reduce but do not eliminate the activity of these proteins.
  • Acquired Hemophilia: This rare form is not inherited. It occurs when the body makes specialized proteins called autoantibodies that attack and disable coagulation factor VIII. This is sometimes associated with pregnancy, immune system disorders, cancer, or allergic reactions to drugs.

Genes Associated with Hemophilia

  • F8
  • F9

Inheritance

Hemophilia A and hemophilia B are inherited in an X-linked pattern. The genes associated with these conditions are located on the X chromosome. In males, who have only one X chromosome, one altered copy of the gene is sufficient to cause the condition. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

In females, who have two X chromosomes, a variant would usually have to occur in both copies of the gene to cause the disorder. However, due to a process called X-inactivation, where one X chromosome is permanently turned off in somatic cells, some females may be affected. If X-inactivation is skewed, a female may have less coagulation factor than usual and be at risk of abnormal bleeding.

Frequently Asked Questions

National Organization for Rare Disorders (NORD)
What is the prognosis of a genetic condition?How can gene variants affect health and development?What does it mean if a disorder seems to run in my family?What are the different ways a genetic condition can be inherited?How are genetic conditions treated or managed? MedlinePlus links to health information from the National Institutes of Health and other federal government agencies. MedlinePlus also links to health information from non-government Web sites. See our disclaimer about external links and our quality guidelines . Genetics Home Reference has merged with MedlinePlus. Genetics Home Reference content now can be found in the "Genetics" section of MedlinePlus. Learn more The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.
HaemophiliaHemophilia, familialHemophilia, hereditary
Genetic Testing Registry: HemophiliaGenetic Testing Registry: Hemophilia b(m)Genetic Testing Registry: Hereditary factor IX deficiency diseaseGenetic Testing Registry: Hereditary factor VIII deficiency disease
Hemophilia is a bleeding disorder that slows the . People with this condition experience prolonged bleeding or oozing following an injury, surgery, or having a tooth pulled. In severe cases of hemophilia, continuous bleeding occurs after minor trauma or even when there is no obvious injury (sometimes called spontaneous bleeding). Serious complications can result from bleeding into the joints, muscles, brain, or other internal organs. Milder forms of hemophilia do not necessarily involve spontaneous bleeding, and the condition may not become apparent until abnormal bleeding occurs following surgery or a serious injury. The major types of this condition are hemophilia A (also known as classic hemophilia or factor VIII deficiency) and hemophilia B (also known as Christmas disease or factor IX deficiency). Although the two types have very similar signs and symptoms, they are caused by variants (also known as mutations) in different genes. People with an unusual form of hemophilia B, known as hemophilia B Leyden, experience episodes of excessive bleeding in childhood but have few bleeding problems after puberty.
The two major forms of hemophilia occur much more commonly in males than in females. Hemophilia A is the most common type of the condition; 1 in 4,000 to 1 in 5,000 males worldwide are born with this disorder. Hemophilia B occurs in approximately 1 in 20,000 newborn males worldwide.
Variants in theF8gene cause hemophilia A, while variants in theF9gene cause hemophilia B. TheF8gene provides instructions for making a protein called coagulation factor VIII. A related protein, coagulation factor IX, is produced from theF9gene. Coagulation factors are proteins that work together in the . After an injury, blood clots protect the body by and preventing excessive blood loss. Variants in theF8orF9gene lead to the production of an abnormal version of coagulation factor VIII or coagulation factor IX, or reduce the amount of one of these proteins. The altered or missing protein . As a result, blood clots cannot form properly in response to injury. These problems with blood clotting lead to continuous bleeding that can be difficult to control. The variants that cause severe hemophilia almost completely eliminate the activity of coagulation factor VIII or coagulation factor IX. The variants involved in mild and moderate hemophilia reduce but do not eliminate the activity of one of these proteins. Another form of the disorder, known as acquired hemophilia, is not caused by inherited gene variants. This rare condition is characterized by abnormal bleeding into the skin, muscles, or other soft tissues, usually beginning in adulthood. Acquired hemophilia results when the body makes specialized proteins called autoantibodies that attack and disable coagulation factor VIII. The production of autoantibodies is sometimes associated with pregnancy, immune system disorders, cancer, or allergic reactions to certain drugs. In about half of cases, the cause of acquired hemophilia is unknown.
Hemophilia A and hemophilia B are inherited in an . The genes associated with these conditions are located on the X chromosome, which is one of the two . In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons. In females (who have two X chromosomes), a variant would usually have to occur in both copies of the gene to cause the disorder. However, in some instances, one altered copy of theF8orF9gene is sufficient, because the X chromosome with the normal copy of the gene is turned off through a process called . X-inactivation occurs early in embryonic development in females. Through this process, one of the two X chromosomes is permanently turned off (inactivated) in somatic cells (cells other than egg and sperm cells). X-inactivation ensures that females, like males, have only one active copy of the X chromosome in each body cell. Usually X-inactivation occurs randomly, such that each X chromosome is active in about half of the body cells. Sometimes X-inactivation is not random, and one X chromosome is active in more than half of cells. When X-inactivation does not occur randomly, it is called skewed X-inactivation. In many females with a variant in one copy of theF8orF9gene, X-inactivation is random and the chromosome with the normal copy of the gene is turned off in about half of cells. These individuals have about half the usual amount of coagulation factor VIII or coagulation factor IX, which is generally enough for normal clotting. However, in some females with anF8orF9gene variant, X-inactivation is skewed, and the chromosome with the normal copy of the gene is turned off in more than half of cells. These individuals can have less coagulation factor VIII or coagulation factor IX than usual and are at risk of abnormal bleeding.
Factor IX assayFactor VIII assayGeneticsHemophilia AHemophilia B
Acquired hemophiliaHemophiliaHemophilia AHemophilia B
ClinicalTrials.gov
HEMOPHILIA A; HEMAHEMOPHILIA B; HEMB
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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