Blood Disorders » Haemophilia

Haemophilia

Haemophilia or Hemophilia refers to any of the many hereditary genetic disorders that impair human body’s ability to check bleeding. It is characterized by lesser plasma clotting factor activity, which is a crucial element required in the formation of the scab on a ruptured blood vessel. On the basis of the type of plasma clotting factor deficiency, Haemophilia can be classified in to type A, B and C. Haemophilia A – the classical haemophilia - is caused due to the deficiency of factor VIII, B or Christmas disease due to retarded production of factor IX, and type C owing to deficient factor XI. In the following paragraphs, we’ll see the genetic aspects of this disease and the chances of it passing over to the next generations.  

The Genetics of Haemophilia

The inheritance of types A and B occurs in an X-linked recessive pattern and they are caused by mutations occurring in the genes that encodes any of the clotting factors. Keep in mind, the genes linked with haemophilia A and B is situated in the X chromosome.

Generally females have two X chromosomes and males possess an X and a Y chromosome. As the mutations leading to haemophilia are recessive, the female carrying the defective gene may not be affected by the disease at all. Instead, the equivalent allele in her chromosome pair will express itself and controls the production of all the required clotting factors. On the other hand, in men, the Y chromosome does not contain any gene that is responsible for the production of factors VII and IX necessary for clotting. Hence, when the pairing X chromosome also becomes deficient, there is no dominant allele in the Y chromosome, and as a result the person develops the illness.  

As the males receive his only X chromosome from his mother, he can be haemophilic depending on two conditions. That is, he has a 50% chance of inheriting the disease if his mother silently carries a deficient gene, and a cent percentage chance if the mother herself is haemophilic in the first place. On the other hand, for a female to inherit the disease, she should get two defective X chromosomes and such a possibility exists only when the father himself is a haemophilic. Therefore, by the law of probability, males are more prone to haemophilia than females. But this trend seems to change a bit nowadays, thanks to advanced treatments available these days, as a result of which more male haemophiliacs are reaching adulthood, and becoming parents.

Apart from inheriting genetically, it is also possible for one to contact haemophilia spontaneously owing to mutations in one of his/her parent’s gametes. Studies show that 1/3 of type A and 1/5 of type B accounts to spontaneous mutations.

Treatment

There is no complete cure for any of the haemophilia types. The only thing one can do is to give regular injections of lacking clotting factors to the patients. In some cases, the haemophiliacs may develop antibodies countering the replacement factors injected into their blood stream. In such cases, non-human factors like the porcine factor VIII are substituted to check bleeding.

In western nations, the common treatment standards fall under two classes - on-demand or prophylaxis. On-demand involves treating bleeding instances when and only they arise. On the other hand, prophylaxis to regular infusion of clotting factors into the patient’s blood stream so as to maintain the clotting levels near to normal to check spontaneous bleeding instances. It is the costliest option of the two.

Recently, recombinant clotting factors have replaced the conventional clotting factors products in the western countries as it is more human-friendly and are safe and pure. But it is very costly and hence is almost not available in the developing world.

Tail Piece: It is estimated that nearly 0.006% of the United States population suffers from haemophilia.

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