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About haemophilia

What is haemophilia?

Haemophilia is a genetic bleeding disorder where the blood doesn’t clot properly. It is caused when blood does not have enough clotting factor. A clotting factor factor is a protein in blood that controls bleeding.

When a person has an injury which causes bleeding, over 20 proteins are involved in the chain reaction to make a clot which stops the bleeding. Two of the key proteins are clotting factor VIII (8) and clotting factor IX (9).

There are two types of haemophilia. Both have the same symptoms.

  • Haemophilia A (also called classical haemophilia) is the most common form, and is caused by having low levels of factor VIII (8)
  • Haemophilia B (sometimes called Christmas Disease) is caused by having low levels of factor IX (9).

There are different levels of severity in haemophilia: mild, moderate and severe. This is linked to the amount of clotting factor in the blood.

There is also another bleeding disorder known as acquired haemophilia, which is not hereditary like the classical form of haemophilia. Click here for more information.

What causes haemophilia?

Everyone has the gene that makes clotting factor VIII (the factor 8 or F8 gene) and the gene that makes clotting factor IX (the factor 9 or F9 gene). These factors are needed for blood to clot.

Haemophilia is caused by a change (mutation or alteration) in the F8 or F9 gene. The gene does not work as well as it should. As a result, the body does not make enough factor VIII (8) or factor IX (9) for blood to clot properly.

Haemophilia is not contagious. It is hereditary and can be passed down from parent to child. Sometimes a person is the first in their family to have haemophilia. This is known as a spontaneous mutation.

How COMMON IS haemophilia?

Haemophilia is rare. It occurs in all races and all socio-economic groups.

In Australia there are more than 3,200 people diagnosed with haemophilia.

Approximately one in 6,000 males has haemophilia A.
Approximately one in 25,000-30,000 males has haemophilia B.

Most females who carry the gene alteration causing haemophilia do not have bleeding symptoms. However, around 20-30% of females with the gene alteration have reduced factor levels and bleeding problems. If their factor levels are low enough, they will have haemophilia, usually mild haemophilia. In some rare cases females can have moderate or severe haemophilia.

Read the HFA haemophilia booklet – PDF 2.5 MB


Date last reviewed: 1 February 2024

Important Note: This information was developed by Haemophilia Foundation Australia for education and information purposes only and does not replace advice from a treating health professional. Always see your health care provider for assessment and advice about your individual health before taking action or relying on published information. This information may be printed or photocopied for educational purposes.

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