When to see a doctor

Seek emergency care if you or your child experiences:

• Signs or symptoms of bleeding into the brain
• An injury in which the bleeding won't stop
• Swollen joints that are hot to the touch and painful to bend

If you have a family history of hemophilia, you may want to undergo genetic testing to see if you're a carrier of the disease before you start a family.

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. Hemophilia occurs when you have a deficiency in one of these clotting factors.

There are several types of hemophilia, and most forms are inherited. However, about 30 percent of people with hemophilia have no family history of the disorder. In these people, an unexpected change (spontaneous mutation) occurs in one of the genes associated with hemophilia.

Acquired hemophilia is a rare variety of the condition that occurs when a person's immune system attacks clotting factors in the blood. It can be associated with:

• Pregnancy
• Autoimmune conditions
• Cancer
• Multiple sclerosis

Hemophilia inheritance

In the most common types of hemophilia, the faulty gene is located on the X chromosome. 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.

This means that hemophilia 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. But some carriers can experience bleeding symptoms if their clotting factors are moderately decreased.