Haemophilia
Haemophilia is an inherited condition causing defective blood clotting. Blood clotting is a complex process involving a number of different factors. There are two types of haemophilia: haemophilia A, where there is deficiency in clotting factor VIII, and haemophilia B (also known as Christmas disease), where there is deficiency in clotting factor IX. The severity of the disease depends on the degree of deficiency, varying from simply prolonged bleeding after injury to severe spontaneous bleeding into joints, causing damage. This is an X - linked condition, which means it is carried by women, who are not affected because they have two X chromosomes. They will, however, pass the disease to their sons if they pass on the defective X chromosome, which they will, statistically, in half of cases. Similarly, half their daughters will become carriers. The sons of sufferers of haemophilia are normal, since they will have received their X chromosome from their mother (provided she is not also a carrier), while all the daughters will be carriers, since they will have inherited the father’s faulty X chromosome. Treatment involves replacement of the missing factor.
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