Haemophilia is a blood disorder where the blood does not clot normally. Haemophilia $\mathrm{A}$ is the most common form, caused by a deficiency of blood clotting factor VIII. Haemophilia B is due to a deficiency of blood clotting factor IX. Haemophilia is an hereditary disorder. In almost all cases, it is males that suffer the condition, although it is passed on by both females and males carrying the gene. Queen Victoria was a carrier of haemophilia A. It is also known as classical haemophilia and factor VIII deficiency haemophilia. Haemophilia B is also known as Factor IX haemophilia, and Christmas disease after the first patient diagnosed with it. Prothrombin producing platelets in such persons are not found in very low concentration.