(Science: disease, haematology) a haemorrhagic diathesis occurring in two main forms:

1. Haemophilia a (classic haemophilia, factor VIII deficiency), an X linked disorder due to deficiency of coagulation factor VIII.

2. Haemophilia b (factor ix deficiency, christmas disease), also X linked, due to deficiency of coagulation factor IX.

Both forms are determined by a mutant gene near the telomere of the long arm of the x chromosome (Xq), but a different loci and are characterised by subcutaneous and intramuscular haemorrhages, bleeding from the mouth, gums, lips and tongue, haematuria and haemarthroses. Congenital tendency to uncontrolled bleeding; usually affects males and is transmitted from mother to son.A human disorder where blood clotting cannot occur. This can result in internal and external bleeding, so sufferers have to be careful. This is caused by chromosomal defects in the x chromosome, and is more common in males due to the lack of opposing domi.

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