April 17: World Hemophilia Day
Edward Johnson, hi-tech and engineering expert, April 17, 2025
What is hemophilia?
Hemophilia is a hereditary bleeding disorder that mainly affects boys, caused by a deficiency in clotting factor VIII (hemophilia A) or IX (hemophilia B). Without these proteins, blood clots poorly, leading to prolonged bleeding, particularly in the joints and muscles.
Transmission of the disease
Hemophilia is caused by a genetic mutation affecting the gene responsible for producing factor VIII (hemophilia A) or factor IX (hemophilia B), both located on the X chromosome. Men, who have only one X chromosome, develop the disease if this gene is altered. Women have two X chromosomes: if one carries the mutation, the other gene is enough to ensure normal clotting. They are therefore not affected, but can pass the mutated gene on to their children. With each pregnancy, they have a one-in-two chance of having an affected son or a daughter who is also a carrier. About a third of cases arise from a spontaneous mutation, with no family history.
Types of hemophilia
About 1 boy in 5,000 is affected by hemophilia A, the most common form, compared to 1 in 30,000 for hemophilia B. A third, very rare type, hemophilia C, results from a deficiency in factor XI; it affects both men and women, but generally causes less severe bleeding. In addition to this classification, the disease is divided into three degrees of severity: severe (less than 1% clotting factor), moderate (1 to 5%) and mild (5 to 40%). A person with severe hemophilia can bleed spontaneously, without trauma, while a mild form causes bleeding mainly during surgery or injury.
Available treatments
Treatment for hemophilia relies on intravenous injection of the missing clotting factor, either factor VIII for hemophilia A or factor IX for hemophilia B. Patients who develop antibodies that neutralize the injected factors, called inhibitors, can receive bypass therapies such as activated factor VII concentrates or monoclonal antibodies, such as emicizumab.