Causes of hemophilia B

What can lead to such a complex bleeding disorder—and why is it more common among males?

Understanding hemophilia B genetics1

Our bodies produce a number of different clotting factors that work together in a sequence to produce a blood clot.

When the body can’t produce enough of the protein called factor IX (factor 9), it can’t control bleeding. A mutation of a gene on the X chromosome causes the factor IX deficiency known as hemophilia B.

Hemophilia B is a sex-linked recessive genetic disorder. That means it can be passed from parents to children via a gene on the X chromosome.

This gene provides instructions for making clotting factor IX. When there is a mutation (change) in this gene, the body does not make the clotting factor properly.

Girls inherit two X chromosomes, one from each parent. Boys inherit an X chromosome from their mother and a Y chromosome from their father. In a boy, the presence of the affected gene results in hemophilia symptoms because there is no second X chromosome that could have a properly working gene.

Father and son hugging each other.

How hemophilia B genetics work

Diagram about how hemophilia B genetics work.

Father does not have hemophilia B

Mother is a carrier of the hemophilia B gene

50% chance sons will have hemophilia B

50% chance daughters will be carriers of the hemophilia B gene

Key of the diagram about how hemophilia B genetics work.

In this example above, each pregnancy has an equal chance of being:

  • a boy with hemophilia
  • a boy without hemophilia
  • a girl carrying the hemophilia B gene
  • a girl not carrying the hemophilia B gene

Keep exploring

Physician discussing treatment options with the patient.

What are the severity levels of hemophilia B?

Pharmacist organizing drawer with medications.

Treatment options for hemophilia B

Man sitting and thinking.

What are hemophilia B symptoms?

  1. Centers for Disease Control and Prevention. What is hemophilia? Accessed February 13, 2023.