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Haemophilia or hemophilia is a name of any of hereditary sex-linked genetic illnesses which cause lowered plasma clotting factor[?] activity that results in compromised blood-clotting. When a blood vessel is injured, the blood will not clot to plug the injury, and the vessel will continue to bleed excessively for a very long period of time. The bleeding can be external[?], if the skin is broken by a scrape, cut or abrasion, or it can be internal[?].


Haemophilia can be controlled quite successfully today by regular injections of a given clotting factor like Factor VIII[?].


The reason that haemophilia mostly affects males is that it is sex-linked. Women have two X-chromosomes whereas men have one X and one Y. It does not matter if there is a defect in a woman's X-chromosome, as the equivalent allele in her other chromosome would express itself and she would not have the illness. However the Y-chromosome in men has no gene for factors VIII or IX. If the recessive gene responsible for blood clotting in a man's X-chromosome is deficient there is no equivalent on the Y-chromosome, so the deficient gene is not masked by the dominant allele and he will develop the illness.

This means also that although women can be carriers of the illness, if men have the gene they also have the illness. It is possible, though rare, for a woman to have the illness, if her father is a haemophiliac and her mother a carrier, or if there is a defect in one of her X chromosomes and she inherits a haemophilia gene from one of her parents. This situation is far more common today than it once was, as improved treatment for haemophilia means that more men survive to adulthood and become parents. Adult women with haemophilia menstruate periodically, so they must take clotting factor to survive.


Haemophilia figured prominently in the history of European royalty. Queen Victoria passed the mutation to her son Leopold and, through daughters, to the royal families of Spain and Russia. For this reason it was once popularly called "the royal disease." See Grigori Rasputin for Alexis.

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