Hemophilia B

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Overview
Hemophilia B (also spelled Haemophilia B or Hæmophilia B) is a blood clotting disorder caused by a mutation of the Factor IX gene. It is the second most common form of haemophilia, rarer than haemophilia A. It is sometimes called Christmas disease after Stephen Christmas, the first patient described with this disease. In addition, the first report of its identification was published in the Christmas edition of the British Medical Journal.

Pathophysiology
Factor IX deficiency leads to an increased propensity for haemorrhage. This is in response to mild trauma or even spontaneously, such as in joints (haemarthrosis) or muscles.

Genetics
The factor IX gene is located on the X chromosome (Xq27.1-q27.2). It is inherited X-linked recessive, which explains why - as in haemophilia A - mostly males are generally affected.

Treatment
Treatment (bleeding prophylaxis) is by intravenous infusion of factor IX.