What Is Haemophilia and How Does It Affects Clotting?
Having haemophilia means your blood cannot clot properly. Contrary to popular belief, this doesn’t mean you are liable to bleed to death from a minor cut, neither would you bleed faster than other people if you get injured. You can, however, bleed for longer. Although bleeding can be from cuts or grazes on the skin, most bleeding that occurs is internal, into muscles and joints.
Derived from the Greek words ‘Haima’ (‘blood’) and ‘philia’ (‘a tendency toward’), haemophilia is caused by a genetic irregularity that is either passed from mother to child or occurs during a child’s development in the womb. Because of the way it is passed from parents to their children the vast majority of people with haemophilia are boys.
Hemophilia occurs in about 1 of every 5,000 male births. Currently, about 20,000 males in the United States are living with the disorder. Hemophilia A is about four times as common as hemophilia B, and about half of those affected have the severe form. Hemophilia affects people from all racial and ethnic groups.
There are two types of haemophilia. Haemophilia A is the most common, affecting one in 5,000 males. Haemophilia B affects about one in 30,000 males. Haemophilia can affect people of any race or nationality and is termed mild, moderate or severe, depending on the level of clotting factor in the blood.
Low levels of clotting factor indicate that ‘spontaneous’ bleeding is more likely to occur. Bleeds are sometimes called ‘spontaneous’ because it is difficult to say what led to the bleeding episode. Normally there is a clear reason for a bleeding episode, whereas ‘spontaneous’ bleeds are usually the result of an accumulation of wear and tear.
The body protects itself from bleeding by producing sticky blood cells called platelets. In people without haemophilia these sticky cells plug any cuts or grazes and then release chemicals that activate biological molecules in the body, which enable the blood to form a clot.
These clotting proteins are known as factors and there are many clotting factors needed for the blood to coagulate (clot) properly and enable bleeding to stop. They do this via a step-by-step process so, if any of the clotting factors are missing, the process doesn’t work properly. The factors are numbered with Roman numerals from I to XIII.
In someone with haemophilia one of the clotting factors required for the blood to clot properly is missing. People with haemophilia A (about 80% of all cases) are lacking in factor VIII and people with haemophilia B (the remaining 20%) lack factor IX.
Hemophilia is caused by a mutation or change, in one of the genes, that provides instructions for making the clotting factor proteins needed to form a blood clot. This change or mutation can prevent the clotting protein from working properly or to be missing altogether. These genes are located on the X chromosome.
Males have one X and one Y chromosome (XY) and females have two X chromosomes (XX). Males inherit the X chromosome from their mothers and the Y chromosome from their fathers. Females inherit one X chromosome from each parent.