What can lead to such a complex bleeding disorder—and why is it more common among males?
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Our bodies produce a number of different clotting factors that work together in a sequence to produce a blood clot.
When the body can’t produce enough of the protein called factor IX (factor 9), it can’t control bleeding. A mutation of a gene on the X chromosome causes the factor IX deficiency known as hemophilia B.
Hemophilia B is a sex-linked recessive genetic disorder. That means it can be passed from parents to children via a gene on the X chromosome.
This gene provides instructions for making clotting factor IX. When there is a mutation (change) in this gene, the body does not make the clotting factor properly.
Girls inherit two X chromosomes, one from each parent. Boys inherit an X chromosome from their mother and a Y chromosome from their father. In a boy, the presence of the affected gene results in hemophilia symptoms because there is no second X chromosome that could have a properly working gene.
Father does not have hemophilia B
Mother is a carrier of the hemophilia B gene
50% chance sons will have hemophilia B
50% chance daughters will be carriers of the hemophilia B gene
In this example above, each pregnancy has an equal chance of being:
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