Hemophilia is a rare, inherited bleeding disorder characterized by the blood’s inability to clot properly. While often perceived as primarily affecting men, women can also be affected by hemophilia, experiencing symptoms ranging from mild to severe. This article explores the genetics of hemophilia and how it affects women.
The Genetics of Hemophilia
Hemophilia A and B are inherited in an X-linked recessive pattern. Males have one X and one Y chromosome. If their single X chromosome carries the altered gene for factor VIII (Hemophilia A) or factor IX (Hemophilia B), they will develop the disorder, as there is no backup copy on the Y chromosome.
Females have two X chromosomes. If one X chromosome carries the altered gene, the other functional X chromosome can produce enough clotting factor to prevent severe bleeding; they are carriers. Carriers do not experience severe symptoms, but they can pass the altered gene to their children.
When Women Are Affected
While many women who carry the hemophilia gene are asymptomatic or experience mild bleeding, some can have significant symptoms. This can occur due to a process called skewed X-inactivation, also known as lyonization. In females, one X chromosome in each cell is randomly inactivated early in development. If the X chromosome with the normal clotting factor gene is preferentially inactivated in a significant number of cells, the X chromosome with the altered gene may remain active, leading to lower clotting factor levels and bleeding symptoms.
In very rare instances, a woman can inherit two altered X chromosomes. They will have hemophilia comparable to affected males. Even women who are carriers can experience mild to moderate bleeding, with 30% of female carriers reporting abnormal bleeding.
Recognizing Symptoms and Diagnosis in Women
Women with hemophilia or carrier status experience a range of bleeding symptoms. Common symptoms include heavy, prolonged menstrual bleeding (menorrhagia), which can lead to anemia. Other symptoms include easy bruising, frequent or prolonged nosebleeds, and extended bleeding after surgical procedures, such as dental work or childbirth. Postpartum hemorrhage (excessive bleeding after delivery) is a concern for women with hemophilia or carrier status.
Diagnosis begins with a review of personal and family bleeding history. Blood tests then measure clotting factor levels, specifically factor VIII and factor IX. Genetic testing can then confirm the gene alteration. Early recognition and diagnosis are important for effective management and to prevent complications.