Haemophilia is an inherited blood clotting disorder, in which one or more of the clotting proteins, called clotting factors are missing or do not work properly.
What is…
Haemophilia is an inherited blood clotting disorder, in which one or more of the clotting proteins, called clotting factors are missing or do not work properly.
When a blood vessel is injured and bleeding occurs, a complex process takes place to stop the bleeding. First small sticky cells called platelets form a plug and then release chemicals that activate the clotting factors. This involves a series of chemical reactions between the clotting factors, which results in the formation of a blood clot. If one of the factors is missing, the sequence of reactions is interrupted and the clotting process will stop. The clotting factors are numbered with Roman numerals from I to XIII e.g. factor VIII and factor IX.
Individuals with haemophilia are not able to form a clot and therefore will bleed for longer. They will not bleed harder or faster than normal.
There is no cure for haemophilia, but it can be effectively controlled with medication.
Types of Haemophilia
The two most common types of haemophilia are haemophilia A and haemophilia B. Haemophilia A is when a person does not have enough factor VIII. It affects about 1 in 5000 people. Haemophilia B, when a person does not have enough factor IX, is less common affecting 1 in 30,000 people.
Haemophilia is divided into three groups, severe, moderate and mild based on the amount of active clotting factor in the blood. See the table below for the details.
People with mild haemophilia usually bleed only as a result of surgery or major injury. They do not bleed often and, in fact, may never have a bleeding problem.
People with moderate haemophilia bleed less frequently, about once a month. They may bleed for a long time after surgery, a bad injury, or dental work. A person with moderate haemophilia will rarely experience spontaneous bleeding.
How Do You Get Haemophilia?
In the UK about 6000 people are known to have haemophilia. Most of these are males because of the way the condition is inherited.
People are born with haemophilia. They cannot catch it from someone like a cold.
Haemophilia is usually inherited, meaning that it is passed on through a parent’s genes. Genes carry messages about the way the body’s cells will develop as a baby grows into an adult. They determine a person’s hair and eye colour, for example.
Sometimes haemophilia can occur when there is no family history of it. This is called sporadic haemophilia. About 30% of people with haemophilia did not get it through their parent’s genes. It was caused by a change in the person’s own genes.
How is Haemophilia Inherited?
The haemophilia gene is passed down from parent to a child. The genes for haemophilia A and B are on the X chromosome. For this reason, haemophilia is called an X-linked (or sex-linked) disorder.
The figure below explains how the haemophilia gene is inherited. When the father has haemophilia but the mother does not, none of the sons will have haemophilia. All the daughters will carry the haemophilia gene.
Women who have the haemophilia gene are called carriers. They sometimes show signs of haemophilia, and they can pass it on to their children. For each child, there is a 50% chance that a son will have haemophilia and a 50% chance that a daughter will carry the gene.
Women can only have haemophilia if their father has haemophilia and their mother is a carrier. This is very uncommon.
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