Causes

When to see a doctor

Seek emergency care if you or your child has:

• 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

When a person bleeds, the body typically pools blood cells together to form a clot to stop the bleeding. Clotting factors are proteins in the blood that work with cells known as platelets to form clots. Hemophilia occurs when a clotting factor is missing or levels of the clotting factor are low.

Congenital hemophilia

Hemophilia is usually inherited, meaning a person is born with the disorder (congenital). Congenital hemophilia is classified by the type of clotting factor that's low.

The most common type is hemophilia A, associated with a low level of factor 8 The next most common type is hemophilia B, associated with a low level of factor 9.

Acquired hemophilia

Some people develop hemophilia with no family history of the disorder. This is called acquired hemophilia.

Acquired hemophilia is a variety of the condition that occurs when a person's immune system attacks clotting factor 8 or 9 in the blood. It can be associated with:

• Pregnancy
• Autoimmune conditions
• Cancer
• Multiple sclerosis
• Drug reactions

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. Females inherit an X chromosome from the mother and an X chromosome from the father. Males inherit an X chromosome from the mother and a Y chromosome from the 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 carriers who have no signs or symptoms of hemophilia. But some carriers can have bleeding symptoms if their clotting factors are moderately decreased.