What can lead to such a complex bleeding disorder? The answer may surprise you.
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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 VIII (factor 8), it can’t control bleeding. A mutation of a gene on the X chromosome causes the factor VIII deficiency known as hemophilia A.1
Hemophilia A is a sex-linked recessive genetic disorder. That means it can be passed from parents to children via a gene on the X chromosome.1
This gene provides instructions for making clotting factor VIII. When there is a mutation (change) in this gene, the body does not make the clotting factor properly.1
Girls inherit 2 X chromosomes, 1 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 might have a properly working gene.1
Father does not have hemophilia
Mother is a carrier of the hemophilia gene
50% chance sons will have hemophilia
50% chance daughters will be carrier of the hemophilia gene
Key
Does not have hemophilia
Carrier of the hemophilia gene
Has hemophilia
Mutated gene
Normal gene
This diagram shows the inheritance pattern of a mother who is a hemophilia A carrier and a father who does not have hemophilia. Each pregnancy has a 25% chance of resulting in a male with hemophilia A, a 25% chance of resulting in an unaffected male, a 25% chance of an unaffected female, and a 25% chance of a female carrier.1 In rare instances, a female may also develop hemophilia A if both of her X chromosomes have the mutation, or 1 is affected and the other is missing or inactive.1
Hemophilia A can also be "acquired" with no family history of the disorder. Acquired hemophilia A occurs when a person's immune system attacks clotting factor VIII in the blood. It can be associated with various conditions, including pregnancy, autoimmune conditions, cancer, multiple sclerosis, and drug reactions. Acquired hemophilia A is very rare, occurring in about 1.5 cases per million persons.
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