Haemophilia

What is haemophilia?

Haemophilia is a bleeding disorder that slows the clotting process. People with the condition often experience prolonged bleeding following injury or surgery and, in severe cases, spontaneous bleeding into joints and muscles. Haemophilia occurs more commonly in males than in females.

Types of this condition include haemophilia A (also known as classic haemophilia) and haemophilia B (also known as Christmas disease). The two types are caused by mutations in different genes.

How common is haemophilia?

Haemophilia A is the most common type of this condition, affecting 1 in 5,000 to 10,000 males worldwide. Haemophilia B is less common; it affects 1 in 20,000 to 34,500 males worldwide.

What genes are related to haemophilia?

Mutations in the F8 and F9 genes cause haemophilia.

Changes in the F8 gene are responsible for haemophilia A, while mutations in the F9 gene cause haemophilia B. The proteins made by these genes play a critical role in the process of blood clotting. Mutations in either gene prevent clots from forming in response to injury, leading to excessive bleeding that can be difficult to control.

How do people inherit haemophilia?

This condition is inherited in an X-linked recessive pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more frequently than females. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

What other names do people use for haemophilia?

• Haemophilia, familial
• Haemophilia, hereditary