Causes

Hemophilia is a bleeding disorder that interferes with the normal clotting of blood. Special proteins called clotting Factors (Factor VIII and IX) help to stop a bleed and repair a damaged blood vessel. For blood to clot, there must be the right amount of Factors VIII and IX in the blood. In hemophilia, the blood is unable to make enough Factor VIII or IX and the blood is unable to clot properly. Hemophilia can be severe or mild depending on how much Factor VIII or IX is missing in the blood.

Genetic material (genes) controls how much Factor VIII or IX is made. In people who have the hemophilia gene, there is a problem with this process. The gene is passed from parent to child.

The chromosomes that determine whether a person is male or female are the X and Y chromosomes (the sex chromosomes). The hemophilia gene is carried on the X chromosome. Girls get two X chromosomes; one from each parent. Boys get an X chromosome from their mother, and a Y chromosome from their father.

Boys are born with hemophilia when they inherit the hemophilia gene from their mother (on the X chromosome). Girls can become hemophilia “carriers” if they inherit the hemophilia gene from their mothers, but they will not have hemophilia (although sometimes carriers have very mild symptoms). These girls will not have full hemophilia because they have the extra X chromosome from their father, which means they can still make clotting factor.

Testing is available for women who suspect they may carry the hemophilia gene.