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Hemophilia

Page history last edited by PBworks 15 years, 12 months ago

Michael Lucciola and Tori Meyer

What is hemophilia?

- Hemophilia is a serious sex-linked genetic disease in which blood does not clot as fast as it should (or at all), and Hemophiliacs can easily bleed to death from a minor injury.

- Hemophilia occurs when there is a mutation in one of the clotting factor genes (ygyh)

- Hemophilia A: The more well known version of Hemophilia, is due to a lack of the antihemophilic factor or factor VIII, a clotting factor which is normally present in the blood in trace amounts and is essential for the formation of natural fibrin. (access)

- Hemophilia B: A similar sex-linked bleeding disorder affecting males but shown through a lack of another blood clotting factor, factor IX (access)

- Both of these types of Hemophilia can only be identified between eachother, which they closely resemble through laboratory tests. (access)

- Approximitally 90% of hemophiliacs have a mutation in the factor VIII gene, Hemophilia A (ygyh)

- 9% have a mutation in the factor XI gene, hemophilia B (ygyh)

- 1% have a mutation on a different clotting factor gene (ygyh)

- About 1 in 4000 men are born with Hemophilia. Women can possibly get it but it is very rare.

What causes hemophilia?

- Hemophilia is caused by a mutation of the clotting factor 8 and the clotting factor 9 or a complete absence of it. Without having this protein present, stable blood clots do not form over the the opened blood vessels quickly and they are easily dislodged from the wound.

- In normal humans:

When the wall of a blood vessel is broken, the vessel constricts it self to lessen blood flow through the vessel and the platelets (larger blood cells) come together towards the opening. As the platelets arrive the blood vessel releases molecules to activate clotting factor 12. Once factor 12 is activated, it instigates a chain reaction that goes from factor 12 to the molecule thrombin (the order is 12, 11, 9, 8, 10, 5, thrombin). When thrombin is activated it then cuts a molecule of fibrinogen into small peices. Once lots of fibrinogen is cut it covers the blood clot stabilizing. For a stable clot to form all of the clotting factor moleculse must be present in the cascade. (all above ygyh)

- In Moderate Hemophilia A

In people with moderate or mild Hemophilia A, the clotting Factor 8 molecule is present but is mutated in a different shape so that it sometimes doesn't fit into the next molecule (clotting factor 10). Since only the Factor 8 molecule is mutated it still can activate Factor 10 causeing people with moderate hemophilia not to bleed as long when injured and rarly or never spontaneously bleed. (all ygyh)

- In Severe Hemophilia A

In people with severe Hemophilia A the clotting Factor 8 protein is usually absent, causing the clotting cycle to stop. (ygyh)

- In Moderate Hempohilia B

In people who have moderate Hemophilia B, they can still have the clotting Factor 8 protein normal and healthy but have a mutated Factor 9 protein which sometimes can activate Clotting Factor 8 even when mutated. (ygyh)

- In Severe Hemophilia B

In People who have severe Hemophilia B, the clotting Factor 9 protein is severly mutated disallowing it to activate clotting Factor 8, halting the clotting chain. (ygyh)

Pictures of how blood clots form in normal humans:

- Hemophilia is sex-linked and carried on the X chromosome. Therefore, only one copy of the hemophilia gene needs to be inherited (in men) for that man to be affected. Women, however, are much less likely to get this disease because women inherit 2 X chromosomes. Women can be carriers, which means they can (and usually will) pass it on to on her children.

History:

The history of hemophilia in the royal families of Europe all began with Queen Victoria of England. Victoria was a female carrier of the hemophiliac gene. Her husband, Prince Albert, was normal. As illustrated in the pedigree chart below, Victoria passed it on to 3 of her children: one affected son and two carrier daughters. Many of Victoria's grandchildren were either affected or carriers, and even more of her great grandchildren inherited the gene. Some of this also came from intermarriage (brothers and sisters marrying, cousins marrying cousins, etc.). (ukgov)

Victoria and Albert's children and grandchildren were married into almost every royal family throughout Europe. Her grandchild Alexandra, a carrier of the hemophiliac gene, married Tzar Nicholas II of Russia. Their son Alexei, the tzarevich, was a hemophiliac. Ironically, the only unaffected monarchy is that of Great Britain (the one of Queen Victoria herself), where there have been no reported cases of hemophilia since Queen Victoria's reign. (ukgov)

Also, in the 1980s, many hemophilia patients were accidentally infected with HIV because there was no US law that required blood to be screened before being used for transfusions. Approximately 50% of hemophilia patients contracted HIV before 1992.

Are there any treatments/cures?

Screening tests for hemophilia are very accurate and can determine which clotting factor is responsible for the disease. Carriers can also be identified by genetic testing. However, there is no cure for Hemophilia.

A treatment used by almost every hemophiliac is injecting onself with purified clotting factors which can prevent excess loss of blood. Early this year, the FDA approved Xyntha, a new factor which has been genetically engineered from Chinese hamster ovary cells. Almost all treatments are very expensive, however, and are only available in more developed countries.

2 Different Approaches to Hemophilia Treatment:

Prophylaxis:

- regularly going for infusions of clotting factors to keep factor levels high to prevent future bleeding episodes

On-Demand:

- waiting for a bleeding episode to occur, and then treating them as they come

Hemophilia patients are also recommended to do regular joint exercises to help protect from excessive bleeding.

Further Information

National and Internation Organizations

National Hemophilia Foundation

www.hemophilia.org

World Federation of Hemophilia

http://www.wfh.org/