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 altered gene on to their daughters but not their sons.
  • Women who carry the altered gene can pass it on to their sons and daughters.
  • Sons with the gene will have haemophilia.
  • Most women and girls who carry the gene have normal clotting factor levels. In some cases they have mildly reduced clotting factor levels. Sometimes their factor levels can be 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 and some may also have haemophilia. They have one X chromosome with the genetic alteration and one unaltered X chromosome.

Haemophilia Genetic Inheritance

Date last reviewed: March 2021