Haemophilia (also spelle as hemophilia, from the Greek haima "blood" and philia "to love") is a group of hereditary genetic disorders that impair the body's ability to control blood clotting or coagulation. In its most common form, Hemophilia A, clotting factor VIII is absent. In Haemophilia B, factor IX is deficient. Hemophilia A occurs in about 1 in 5,000–10,000 male births, while Hemophilia B occurs at about 1 in about 20,000–34,000.