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Medical Author:

Troy S Cutler, MD

Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Hemophilia Causes

• Men have only one X chromosome. If that chromosome carries the abnormal hemophilia gene, the man will have the disease hemophilia. Both hemophilia A and B are linked to the X chromosome, which means they primarily affect men.
  
  
• Women have two X chromosomes. Even if one of the X chromosomes carries the defective gene, the normal gene on the other X chromosome will protect the woman from hemophilia. The gene does not affect them, but they carry it and pass it on to their children.
  
  
  • If a woman is a carrier, she has a 50% chance that her sons will have hemophilia. Likewise, she has a 50% chance that her daughters will be carriers of hemophilia. This assumes that the woman's partner is not a hemophiliac.
    
    
  • A man who has hemophilia has a 100% chance that his daughters will be carriers, since they must inherit the defective x chromosome from the father. His sons will not be affected if the mother is not a carrier.
  
  
• The transmission of this gene to offspring accounts for 70% of the cases of hemophilia. The remaining 30% occur from spontaneous changes in genes responsible for causing hemophilia.