Virtual Medical Centre

Haemophilia A

• What is Haemophilia A?
• Who gets Haemophilia A?
• Predisposing Factors
• Progression
• Probable Outcomes
• How is Haemophilia A Diagnosed?
• How is Haemophilia A treated?
• Haemophilia A References

What is Haemophilia A?

Haemophilia A involves a genetic defect causing abnormality of blood clotting. Normal blood contains a range of special proteins and chemicals that cause blood to clot quickly if blood vessels are damaged. This occurs due to a sequence of events known as the 'coagulation cascade', involving a series of reactions between different coagulation 'factors'. The end result is a mesh of protein called 'fibrin', which is the solid part of a clot, and plugs up the damaged vessel.

In Haemophilia A, levels of a coagulation factor called Factor VIII are reduced. This occurs due to genetic defects in the gene coding for this protein.

Who gets Haemophilia A?

The prevalence of heamophilia A is about 1 in 5000 in the male population. It is only present in males because the gene for Factor VIII is on the X chromosome; males only inherit one X chromosome, and so if this has the defect, then they will suffer haemophilia. Females inherit two X chromosomes, and so even if one has the defect, they will not suffer from haemophilia, as the other chromosome has a normal Factor VIII gene.

Females with one abnormal X chromosome are called 'carriers'. If a female carrier has a son, he has a 50% chance of having haemophilia, and a daughter has a 50% chance of being a carrier. All daughters of haemophiliacs are carriers and the sons are normal.

Predisposing Factors

As explained above, a family history is clearly a predisposing factor for haemophilia. In addiotion, about one-third of cases are 'sporadic', meaning that the genetic defect occurs for unknown reasons, without being passed on from the patient's parents.

Progression

As the disease arises from an abnormality in a gene coding for a protein that is important to coagulation throughout life, haemophilia is an immediate, constant and unremitting disease. However, cases vary in severity, depending on the level of Factor VIII in the body.

In milder cases, diagnosis may not be made until quite late in life. In addition, effective treatment is available, meaning that patients may show considerable improvement once this has begun.