Haemophilia inheritance

How is haemophilia passed on?

Haemophilia is an inherited condition and occurs in families; however, in 1/3 of cases it appears in families with no previous history of the disorder. The genetic alteration causing haemophilia is passed down from parent to child through generations.

  • Men with haemophilia will pass the gene alteration on to their daughters but not their sons.
  • Women who carry the gene alteration can pass it on to their sons and daughters.
  • Sons with the gene alteration will have haemophilia.
  • Most women and girls who carry the gene alteration have normal clotting factor levels. Around 20-30% have reduced clotting factor levels. Sometimes their factor levels are low enought to be classified as having haemophilia, usually mild haemophilia. In a few very rare cases girls and women can have extremely low factor levels and have severe haemophilia.
Read more - can females have haemophilia?

The diagrams below may assist in understanding inheritance in haemophilia.
  • The red males have haemophilia
  • The red and blue females carry the gene alteration and some may also have haemophilia. They have one X chromosome with the gene alteration and one unaltered X chromosome.

Haemophilia Genetic Inheritance

Date last reviewed: May 2022
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.