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.

• 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.