What causes haemophilia?

When blood clots, a chain reaction involving several different substances, called clotting factors, takes place. In people with haemophilia, one of these clotting factors does not work properly. The symptoms of the disorder can range from severe to mild, depending on how active the clotting factor is. In people affected by haemophilia the gene instructions for these clotting factors are altered or missing.

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A blood clot.

How is haemophilia inherited?

Genes found on the X-chromosome cause haemophilia, so the disorder usually affects only boys. In some cases, the disorder appears 'out of the blue', following a genetic change in the unfertilised egg. In other cases, the affected boy inherits haemophilia from his carrier mother. A carrier woman has a one-in-four chance of having an affected son, and a one-in-four chance of having a carrier daughter. About a third of carrier women have mild symptoms themselves.

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Inheritance of haemophilia.

How is haemophilia treated?

Since the 1970s, doctors have successfully treated people with haemophilia by injecting them with clotting factors which can be purified from donated blood. Unfortunately, many people have been infected with viruses after receiving clotting factors made from infected blood. In Doctors now test and heat-treat donated blood to ensure its safety. In the future, haemophilia may be treated using clotting factors produced by genetically engineered bacteria.

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Boy with haemophilia playing table football.

 

Principal Funder:

Wellcome trust

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