Haemophilia

Haemophilia (British English), or hemophilia (American English) (from Ancient Greek αἷμα (haîma) 'blood' and φιλία (philía) 'love of'), is a mostly inherited genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. This results in people bleeding for a longer time after an injury, easy bruising, and an increased risk of bleeding inside joints or the brain. Those with a mild case of the disease may have symptoms only after an accident or during surgery. Bleeding into a joint can result in permanent damage while bleeding in the brain can result in long term headaches, seizures, or an altered level of consciousness.

There are two main types of haemophilia: haemophilia A, which occurs due to low amounts of clotting factor VIII, and haemophilia B, which occurs due to low levels of clotting factor IX. They are typically inherited from one's parents through an X chromosome carrying a nonfunctional gene. Most commonly found in men, haemophilia can affect women too, though very rarely. A woman would need to inherit two affected X chromosomes to be affected, whereas a man would only need one X chromosome affected. It is possible for a new mutation to occur during early development, or haemophilia may develop later in life due to antibodies forming against a clotting factor.

Other types include haemophilia C, which occurs due to low levels of factor XI, Von Willebrand disease, which occurs due to low levels of a substance called von Willebrand factor, and parahaemophilia, which occurs due to low levels of factor V. Haemophilia A, B, and C prevent the intrinsic pathway from functioning properly; this clotting pathway is necessary when there is damage to the endothelium of a blood vessel. Acquired haemophilia is associated with cancers, autoimmune disorders, and pregnancy.