Hemophilia is a group of hereditary genetic disorders that impair the body’s ability to control blood clotting or coagulation, which is used to stop bleeding when a blood vessel is broken. When a blood vessel is injured, a temporary scab does form, but the missing coagulation factors prevent fibrin formation, which is necessary to maintain the blood clot.

The most common symptom of hemophilia is bleeding, particularly into the joints and muscles. When a person with hemophilia is injured, he does not bleed faster than a person without hemophilia, but it takes longer for bleeding to stop. Bleeding also may start again several days after an injury or surgery. Surface bruises and/or small cuts usually are not a problem, but deeper injuries may result in bleeding episodes that can lead to permanent disability unless they are treated promptly. Other symptoms of hemophilia include bruising easily, prolonged nosebleeds, or vomiting of blood.

Hemophilia A and B are caused by genetic mutations in the gene for factor VIII or factor IX. Mutations are abnormal changes that occur in a gene. The gene for factor VIII and factor IX is located on the X chromosome, making Hemophila A and B X-linked disorders. As such, one copy of the abnormal factor VIII or factor IX gene results in hemophilia in males, and a carrier state in females.

When there is a family history of hemophilia, the mother usually is a carrier and half of her sons and some of her male relatives will have hemophilia. If there is no family history of hemophilia, the disorder is due to a new mutation that occurred either in the affected individual, or in the individual’s mother, whose carrier state may have gone unnoticed.

Hemophilia may occur in mild, moderate and severe forms, based on both clinical symptoms and the level or amount of clotting factor in the blood.

• An individual with mild hemophilia has 6% to 49% of the normal factor level, and usually bleeds only after serious injury, trauma or surgery. The first episode of bleeding may not occur until adulthood.
• An individual with moderate hemophilia has 1% to 5% of the normal factor level and has bleeding episodes after injuries, major trauma or surgery. He also may experience occasional bleeding without obvious cause, called spontaneous bleeding episodes.
• An individual with severe hemophilia has less than 1% factor level and experiences bleeding following an injury or surgery, and may have frequent spontaneous bleeding episodes into the joints and muscles.

A person’s severity of hemophilia does not change over time because factor level is determined by genetics. If a person cannot make clotting factor when he is young, he will never have the ability to make clotting factor.

Though there is no cure for hemophilia, it can be controlled with regular infusions of the deficient clotting factor, i.e. factor VIII in hemophilia A or factor IX in hemophilia B. Factor replacement can be either isolated from human blood serum, recombinant, or a combination of the two. Some hemophiliacs develop antibodies (inhibitors) against the replacement factors given to them, so the amount of the factor has to be increased or non-human replacement products must be given, such as porcine factor VIII.