Hemophilia A causes
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fahd Yunus, M.D. [2]
Overview
Hemophilia A is caused by an inherited X-linked recessive trait, with the defective gene located on the X chromosome.
Causes
Females have two copies of the X chromosome, so if the factor VIII gene on one chromosome is defective, the gene on the other chromosome can compensate by producing sufficient factor VIII. Males, however, have only one X chromosome. Thus, if the factor VIII gene on that chromosome is defective, they will have hemophilia A. Therefore, most people with hemophilia A are male. If a woman has a defective factor VIII gene, she is considered a carrier. This means the defective gene can be passed down to her children. Boys born to a woman who carries the defective gene have a 50% chance of having hemophilia A, while their daughters have a 50% chance of being a carrier. All female children of men with hemophilia A carry the defective gene.