Understanding Hemophilia -- the Basics

Problems Caused by Hemophilia

Internal bleeding resulting from hemophilia may lead to several health problems, including:

• Joint deformity: People with severe hemophilia may suffer spontaneous bleeding in the joints. People with less severe hemophilia may have bleeding in a joint if they fall or are injured. If joint bleeds are not promptly and adequately treated, joint deformity can occur. Bleeding in a joint can cause scarring in the joint. With repeated bleeds, the joint may lose mobility and becomes susceptible to further bleeding. The knee, ankle, and elbow joints are most commonly affected. Bleeding into the muscles of the legs can also be severely disabling.
• Blood in urine: Blood in the urine may occur on occasion, due to bleeding within the kidneys.
• Problems breathing: Breathing problems can occur as a result of bleeding into the throat. If not promptly treated, bleeding in the throat can interfere with breathing so much that a patient may need to be put onto a ventilator until the bleeding stops and swelling goes down.
• Brain damage: Bleeding in the brain may cause permanent brain damage and disability or even death. While usually caused by trauma, in very severe cases of hemophilia, these areas may bleed without known injury.

What Causes Hemophilia?

Hemophilia is a genetic disease linked to a defective gene on the X chromosome. Chromosomes come in pairs -- women have two X chromosomes while men have one X and one Y chromosome.

A woman who has the defective gene is called a "carrier" -- she carries the disease and can pass it to her children. In most cases, though, the woman has no symptoms of hemophilia. When a woman who is a carrier has a son, the son receives one X chromosome from his mother, so he has a 50% chance of receiving the defective gene (and a 50% chance of receiving a normal copy of the gene). Boys who receive the defective gene have hemophilia. Likewise, when a woman who is a carrier has a daughter, the daughter has a 50% chance of receiving the defective gene and, thus, being a carrier herself.

Men who have hemophilia do not pass the disease to their sons because boys inherit only a Y chromosome from their father. However, men do pass their X chromosome, and thus a defective gene, to each of their daughters, so each of their daughters is a carrier.

If the father has hemophilia and the mother is a carrier, there is a chance the daughter will have hemophilia.

About 70% of people who have hemophilia can trace hemophilia back through their family for multiple generations. In about 30% of newly diagnosed infants with hemophilia, no other family member is known to have had hemophilia. In these cases a mutation or change has occurred in the factor VIII or factor IX gene. From the time of the mutation, the affected person can transmit the defective gene to his or her children.