When you bleed, your body normally pools blood cells together to form a clot to stop the bleeding. The clotting process is encouraged by certain blood particles (platelets and plasma proteins). Hemophilia occurs when you have a deficiency in one of these clotting factors.

Hemophilia is inherited. However, about 30 percent of people with hemophilia have no family history of the disorder. In these people hemophilia is caused by a genetic change (spontaneous mutation).

There are several types of hemophilia. They are classified according to which clotting factor is deficient:

  • Hemophilia A, the most common type, is caused by insufficient clotting factor VIII.
  • Hemophilia B, the second most common type, is caused by insufficient clotting factor IX.
  • Hemophilia C, in which signs and symptoms are often mild, is caused by insufficient clotting factor XI.

Hemophilia inheritance

Everyone has two sex chromosomes, one from each parent. A female inherits an X chromosome from her mother and an X chromosome from her father. A male inherits an X chromosome from his mother and a Y chromosome from his father.

Hemophilia inheritance depends on your type of hemophilia:

  • Hemophilia A or B. The gene that causes them is located on the X chromosome, so it can't be passed from father to son. Hemophilia A or B almost always occurs in boys and is passed from mother to son through one of the mother's genes. Most women with the defective gene are simply carriers and experience no signs or symptoms of hemophilia. Women can experience bleeding symptoms if their factor VIII or IX is moderately decreased.
  • Hemophilia C. This disorder can be passed on to children by either parent. Hemophilia C can occur in girls and boys.
Sep. 11, 2014

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