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Haemophilia is passed on in an X-linked recessive fashion.

Haemophilia is a blood condition that means bleeding does not stop. The bleeding occurs because the blood does not clot. A person with a small cut or internal bleed (bruise) could bleed to death. They do not bleed more than a normal person, but they bleed for much longer. The word comes from the Greek words haima "blood" and philia "to love"[1]

It usually affects males. It is passed from mother to child through genes.

There are 3 types of haemophilia:

  • Haemophilia A - about 90% of cases. There is no blood clotting ability.
  • Haemophilia B - not as severe, but much less common. There is not enough blood clotting ability.
  • Haemophilia C - caused by not one, but two recessive (weak) genes.

Haemophilia A happens in about 1 in 5,000–10,000 male births.[2] Haemophilia B happens in about 1 in every 20,000–34,000 male births.

This happens because each male needs a X and a Y chromosome; but because the Y chromosome is smaller than the X chromosome, some genes are missing. Most importantly in haemophilia, it is the H gene that is missing. If gene h (from the X chromosone) is recessive (weak) then it would be replaced by the gene H (from the Y chromosone). But when gene H is missing from the Y chromosone then gene h, the weak one from the X chromosone, takes its place and causes haemophilia. There is no cure for this disease but there are different treatments available around the world.

A person with haemophilia is called a haemophiliac.

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