Hemophilia

Introduction

Hemophilia is a rare genetic blood clotting disorder that primarily affects males. People living with hemophilia do not have enough of, or are missing, one of the blood clotting proteins naturally found in blood. Two of the most common forms of hemophilia are A and B. In persons with hemophilia A (also called classic hemophilia), clotting factor VIII is not present in sufficient amounts or is absent. In persons with hemophilia B (also called Christmas disease), clotting factor IX is not present in sufficient amounts or is absent. People with hemophilia do not bleed more profusely or bleed faster than normal; they bleed for a longer period of time.

Virtually all people who have hemophilia A or B are born with it. The majority of people with hemophilia

have a family history (it is a hereditary disorder).

In as many as 30% of cases, there is no family history of hemophilia. In these cases, the mother may not be aware that she carries the gene for hemophilia, or a gene mutation may have occurred spontaneously.

A long history

Hemophilia was identified as early as biblical times. Doctors in medieval times were familiar with it as well. In 1803, a Philadelphia doctor published the first description of hemophilia in the United States.

But it was not until 30 years later that hemophilia became widely recognized. Hemophilia later

developed a reputation as the "royal disease" because it passed from Queen Victoria of England to her descendants throughout the royal houses of Europe.

Who Gets Hemophilia?

Hemophilia occurs when the gene to produce clotting factor does not work correctly.

Without the proper amount of clotting factor, bleeding occurs easily.

Hemophilia is an inherited disorder in about two thirds of the cases. About one third of

the cases of hemophilia occur due to spontaneous changes in the gene or mutations.

The presence of a mutated gene may not be noted until a woman with no family

history of hemophilia has a son with the disorder.

The gene for hemophilia is carried on the X chromosome. The gene for hemophilia is

also recessive. This is why hemophilia is referred to as an X-linked recessive disorder.

If there is not a normal gene present to offset the defective, recessive gene, the

disorder will be present. Whether or not a child will have hemophilia or be a carrier for

the disorder depends on the status of the mother and of the father. The figure below

shows how this type of disorder is inherited.

Males have an X chromosome and an Y chromosome. The X chromosome comes from

the mother and the Y chromosome comes from the father. If the mother has a

defective gene, the son's chance of having hemophilia is 50%, depending on which X

chromosome is inherited. A son cannot inherit the disorder from his father, even if the

father has hemophilia.

Females have two X chromosomes. One X chromosome comes from the mother and

one comes from the father. All daughters of men with hemophilia will be carriers.

Carriers rarely have the disorder but are able to pass the defective gene to their

offspring. The daughter also has a 50% chance of becoming a carrier if the mother is a

carrier, depending on which X chromosome is inherited.

In most cases, one of the daughter's two X chromosomes is normal. Most females

with a gene for hemophilia do not have symptoms of the disorder because a normal

gene offsets any problems caused by