Hemophilia

Hemophilia: (Amy and Cameron) Hemophilia is caused by an X1 chromosome deficiency which controls the number of platelets in your blood. It is more common in men than women because men only have one X chromosome and women have two. If a women has one defective X chromosome and one healthy one she can rely on the healthy one and be a carrier of the disease instead of an afflicted person. Usually, it can only be inherited if both parents contribute a defective gene. People with hemophilia may bleed from any place in their body and at any time. They will normally bleed after bruising or scraping but no contact is required to make them bleed. Most of their bleeding happens internally. Most of the time they bleed into their joints which causes them to be painful, swollen, and stiff. They can bleed into their esophogus, stomach, intestines, urine, and even brain in more serious cases. They can also bleed from their gums and nose and in women it can recognized as having a very heavy period.

There are two types, hemophilia A and hemophilia B. Hemophilia A is caused by a defect in the Factor VIII Gene, whereas hemophilia B is caused by a mutation in the Factor IX Gene. These genes control blood clotting. Hemophilia A is the more common type, occurring in 90% of cases.

Below is an image of how hemophilia is transmitted: Hemophilia transmission. <[|http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookhumgen.html>.] 4/10/07. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com)

The above image shows how hemophilia can be transmitted if a male has it, but the female does not. Since hemophilia is a sex-linked recessive trait, it takes two defective X chromosomes in females to cause it, but only one in males. This is why the male in the above diagram has the disease. The woman in the above diagram does not have the disease, nor is she a carrier. As the image shows, the male passes his traits to his daughters, who all become carriers of the disease. The female passes her traits to her sons, who are all normal.

Many famous European people and families had hemophilia. Queen Victoria of England was a carrier of the disease (meaning she only had one mutated X chromosome) and because of the intermarriage in Europe, it was passed to the royal family of Russia. Some speculate that Queen Victoria was the cause of the downfall of the Russian monarchy, since she passed hemophilia on to Czar Nicholas' son, Alexei.