Haemophilia is a disorder of the blood-clotting system.
Normally, when you cut yourself your blood plugs the wound by changing from a liquid to a solid and forming a blood clot. If you have haemophilia, your blood will not clot normally and you may bleed for longer than normal, or you may bleed internally, particularly into joints such as your knees, elbows and ankles.
Blood contains special proteins, called 'clotting factors', which are involved in the clotting process. There are 20 different clotting factors If you have haemophilia, your body does not produce enough, or produces none, of one of these clotting factors.
There are different types of haemophilia. If you have haemophilia A, you have a deficiency of clotting factor VIII (known as factor VIII). Haemophilia A is also known as classical haemophilia and is the cause of about 80% of cases. If you have haemophilia B, you have a deficiency of clotting factor IX (known as factor IX).
Haemophilia B is also known as Christmas disease and is the cause of about 20% of cases. Deficiencies of factors VIII and IX are the most common; deficiencies of other factors do exist but are very rare.
Haemophilia can be mild, moderate or severe, depending on how much factor VIII or IX is missing from your blood:
· Mild haemophilia - your blood contains 5-25% per cent of the normal amount of factor VIII or IX.
· Moderate haemophilia - your blood contains 1-5% of the normal amount of factor VIII or IX.
· Severe haemophilia - your blood contains less than 1% of the normal amount of factor VIII or IX.
Haemophilia is rare and almost always affects men. Haemophilia A occurs in about 1 in 10,000. Haemophilia B occurs in about 1 in 40,000.
The signs and symptoms of haemophilia vary, depending on the severity of the clotting factor deficiency. They include:
· bleeding from cuts or injuries that continues for much longer than normal,
· unexplained bleeding, bruising or nosebleeds,
· unusually large or deep bruising forming as a result of injury,
· joint painor swelling, or a feeling of warmth in the joint, and
· blood in the urine or faeces.
Internal bleeding into the joints, muscles or other tissue can occur spontaneously (without an external cause), or as a result of an injury.
The joints most commonly affected by internal bleeding are the knees, followed by the elbows, ankles, shoulders and wrists. If left untreated, bleeding into a joint causes a feeling of warmth or tightness in the joint,pain,swelling and spasm of the muscles surrounding.
Once a joint has suffered a 'bleed', it is more likely to bleed in the future. Repeated bleeding in a joint can lead to arthritis or permanent joint damage, causing stiffness and mobility problems.
Bleeding can occur in or around the brain or spinal cord. This is rare and usually occurs only in those with severe haemophilia, but occasionally it can occur in those with the mild or moderate forms of the condition. This type of bleeding is normally caused by injury to the head or spine, but it can occur spontaneously. Bleeding into the brain can cause headache, nausea, vomiting and seizures (fits).
How easily or badly a person with haemophilia bleeds depends on the severity of their haemophilia. In those with mild haemophilia, bleeding often occurs only after moderately severe injury or after surgery. Children with mild haemophilia may not have any noticeable symptoms for years. However, those with severe haemophilia may experience spontaneous bleeding as often as 30 or more times a year.
Haemophilia is caused by a deficiency of one of the clotting factors involved in the blood clotting process, most commonly factor VIII or IX. The production of these factors is controlled by a gene ; if the gene has a defect it can lead to not enough of the factor being produced.
Haemophilia can be inherited because the defective gene can be passed on from parent to child. About 70% of cases of haemophilia are inherited.
Everyone has two sex chromosomes- they inherit one from each parent. Females inherit an X chromosome from their mother and an X chromosome from their father. Males inherit an X chromosome from their mother and a Y chromosome from their father.
The gene that controls the production of factor VIII and IX is located on the X chromosome. As a man only has one X chromosome, if that chromosome carries the defective gene they will have haemophilia. Men cannot pass on the gene that causes haemophilia to their sons. Haemophilia is passed from mother to son via the X chromosome.
Most women who inherit an X chromosome with the defective gene will have a normal version of the gene on their second X chromosome - only if both their inherited X chromosomes have the defective gene will they have haemophilia.
Women who have the defective gene on only one of their X chromosomes normally develop no symptoms of haemophilia and are known as carriers of the condition. Women who are carriers have a 50% chance that their sons will have haemophilia.
In about 30% of cases there is no family history of haemophilia. These cases are the result of the gene responsible for producing factor VIII or IX mutating spontaneously, either in a man's sperm or a woman's egg. A mutated gene is often defective, so if a sperm or egg with the mutated gene is fertilised, the child may have haemophilia.
To diagnose haemophilia, a doctor will take a family history, ask about any history of abnormal bleeding and take a blood sample that can be tested to identify any problems with the blood clotting process.
Blood tests can identify whether the blood has low levels of any of the clotting factors or whether one of the factors is missing entirely. They can also measure the 'clotting time' of the blood. Normal clotting time is between four and seven minutes, but in a person with haemophilia it will be longer.
The results of these tests will show if the person has haemophilia, what type of haemophilia they have, and whether it is mild, moderate or severe.
A blood tests can also identify women who are carriers of the gene that causes haemophilia. This means that a woman who wants to become pregnant and who has a family history of haemophilia can be tested to find out whether she is a carrier.
Women who are carriers and who are already pregnant can be given an ultrasound scan to find out the sex of the baby. If it is a boy, they can then decide whether to have an amniocentesis or Chorionic Villus sampling test that will show whether their child has haemophilia.
There is no cure for haemophilia. Treatment for the condition is based on 'replacement therapy' - replacing the clotting factor that is too low or missing.
For those with mild haemophilia, cuts and grazes usually cause few problems as gentle pressure on the wound is normally enough to stop any bleeding. If necessary, mild haemophilia A can be treated with an injection of the hormone desmopressin, which stimulates the body's production of clotting factor VIII. Replacement therapy is not normally needed for mild haemophilia.
Moderate to severe haemophilia can be treated with an injection of replacement clotting factor. Unfortunately, replacement clotting factor remains active for only a short period - it loses half its activity after only 12 hours - so if the bleeding is serious, repeated injections are necessary. Injections can be given in hospital, but many people with haemophilia are taught to inject themselves at home.
Replacement clotting factor can be given as needed, or regular injections can be given two or three times a week to keep the levels of clotting factor in the blood high enough so that bleeding does not occur. This can reduce the amount of time those with severe haemophilia need to spend in hospital and minimise the likelihood of long term joint damage.
For many years replacement clotting factors were made from donated human blood. However, as a precaution against the theoretical risk from Creutzfeldt-Jakob disease, synthetic alternatives called 'recombinant factors' are now used.
Recombinant factors are regarded as free from the risk of blood infections as well as the theoretical risk from CJD.
The most common complication of haemophilia is arthritis or permanent joint damage due to repeated bleeding within the joint. This can cause long-term pain and loss of mobility.
Some people with haemophilia can develop antibodies to the replacement clotting factors used to treat the condition. The antibodies can destroy the clotting factor before it has a chance to work. This can be a serious problem as it means that the main treatment for haemophilia is no longer effective.
When antibodies develop, doctors may use larger doses of clotting factor or try different types of factor. Antibodies to clotting factor develop in about 20% of those with severe haemophilia A, and about 1% of those with haemophilia B.
Before the dangers of the AIDS epidemic were fully recognised, blood containing the HIV virus was used to produce replacement clotting factors and many haemophiliacs acquired the disease between 1979 and 1985. Hepatitis has also been a problem in the past, with many haemophiliacs contracting the disease from blood carrying the virus.
Blood donors are now carefully screened and all donated blood products tested for these viruses. Blood products used to create clotting factors are treated with a detergent and heated to destroy viruses.
Vaccination against hepatitis A and B is also offered to all haemophiliacs. In recent years synthetic alternatives to clotting factors made from human blood have become available. Known as recombinant clotting factors, they are regarded as free from the risk of any blood infections as well as the theoretical risk from Creutzfeldt-Jakob disease (CJD).