Hemophilia is a rare hereditary disorder that prevents blood from clotting. Internal or external bleeding that does not stop can damage organs and joints. Hemophilia is the result of a genetic problem that causes babies to have absent or low levels of a certain clotting factor. About 18,000 Americans have hemophilia, according to the U.S. Centers for Disease Control and Prevention (CDC). The majority of individuals affected by this condition are males.

Normally, a break in a blood vessel is followed by a complex set of reactions that cause the blood to form a plug known as a clot. The clot is able to reduce or stop bleeding until the wound heals. Proteins called clotting factors are an essential part of this process.

People with hemophilia have a deficient amount of some type of clotting factor. This can result in prolonged bleeding following an injury. Bleeding can also occur internally, and the loss of excessive amounts of blood can damage internal organs. Such bleeding into a vital organ, such as the heart or brain, can be fatal.

There are three types of inherited hemophilia:

• Hemophilia A. About 90 percent of people with hemophilia have this version of the disorder.
  
  
• Hemophilia B. About 10 percent of people with hemophilia have this version of the disorder.
  
  
• Hemophilia C. This type of hemophilia is rare in the United States.

Hemophilia A and B usually are passed from mother to son. A damaged gene on the X chromosome is responsible for these forms of hemophilia. All females inherit two X chromosomes, one from each parent. If only one X chromosome is affected, the other can provide the necessary clotting factor. Males inherit an X chromosome from their mothers and a Y chromosome from their fathers. If the X chromosome has the affected gene, the male will have hemophilia because the Y chromosome has no gene to compensate for the missing clotting factors. 

The process for developing the extremely rare hemophilia C is different, and both males and females can get this form of the disorder.

Patients with hemophilia are at risk of continual bleeding following an injury. In some cases, this bleeding is visible or is apparent from bruising of the skin. Bleeding that is internal may not be visible. Joints in the knees, ankles and elbows are particularly vulnerable to internal bleeding. Internal bleeding may create a tingly or bubbly sensation in the joint. The joint also may be warm to the touch.

In diagnosing hemophilia, a physician will perform a complete physical examination and compile a thorough medical history. A family history of hemophilia can significantly increase the chance that a patient may have this disorder. Blood tests may be ordered to measure levels of clotting factor and to monitor how long it takes blood to clot.

There is no cure for hemophilia. The main treatment is injections of the clotting factor that the patient is missing. Patients with hemophilia may need to make several lifestyle adjustments as a result of their condition. However, most patients are able to live full, active lives.