People with hemophilia are born with it. It is caused by a fault in one of the genes that determine how the body makes blood clotting factor VIII or IX. These genes are located on the X chromosome.
To understand how hemophilia is inherited, it is important to learn about chromosomes.
In humans there are 23 pairs of chromosomes, including the sex chromosome pair. There are two types of sex chromosome:
All humans have a pair of sex chromosomes:
What chromosomes do we inherit from our parents?
(Before reading on, remember that the faulty gene is never on the Y chromosome. If it is present, it will be on the X chromosome.)
If the father has hemophilia and the mother has no faulty gene (is not a carrier):
Father (Y + Xfaulty). Mother (X + X).
If the father does not have hemophilia and the mother has a faulty gene:
Father (Y + X). Mother (X + Xfaulty).
Approximately one third of patients with hemophilia have no family history of the disease, either because of new genetic mutations, or because previous affected generations either had daughters (who were carriers) or sons who died in early childhood from hemophilia or any other cause or who were not affected.
Disclaimer: This informational section on Medical News Today is regularly reviewed and updated, and provided for general information purposes only. The materials contained within this guide do not constitute medical or pharmaceutical advice, which should be sought from qualified medical and pharmaceutical advisers.
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