Haemophilia is caused by an inherited genetic mutation.

It mainly affects males due to the way it’s passed from a parent to their child.

A genetic mutation occurs when the normal instructions carried in certain genes become “scrambled”. This means that some of the body’s processes will not work in the normal way.

The type of mutation determines how severe the symptoms will be, so the condition will always be the same severity within a family.

Chromosomes

To understand how haemophilia is inherited, it is useful to know about chromosomes.

Chromosomes are blocks of DNA. They contain a detailed set of instructions that control a wide range of factors, including how the body’s cells develop and the baby’s sex.

There are two types of sex chromosomes: the X chromosome and the Y chromosome. All humans have a pair of sex chromosomes. Men have an XY pair and women have an XX pair.

Boys inherit their X chromosome from their mother and their Y chromosome from their father. Girls inherit an X chromosome from each parent.

Haemophilia is inherited through a mutation in the X chromosome.

How the mutation is inherited

The chances of a child inheriting the haemophilia mutation depend on which of their parents has the mutated gene.

Only the mother is affected

If a woman with the mutated X chromosome and an unaffected man have a baby, there is a:

• one in four chance of having an unaffected baby boy
• one in four chance of having a baby boy with haemophilia
• one in four chance of having an unaffected baby girl
• one in four chance of having a baby girl with one affected chromosome

In the last situation, the girl will become a carrier of the mutated gene. This means she can pass it on to her children, but she will not usually have any severe symptoms of haemophilia herself. However, female carriers sometimes have some bleeding problems, such as heavy periods.

Only the father is affected

If a man with haemophilia has a son with an unaffected woman, there is no chance that the boy will get haemophilia. This is because he will always inherit his X chromosome from his mother.

However, any daughters that the man has will become carriers of the mutated haemophilia gene and may pass it on to their children. 

Both parents are affected

If a woman with the mutated chromosome and a man with haemophilia have a baby, there is a:

• one in four chance of having an unaffected baby boy
• one in four chance of having a baby boy with haemophilia
• one in four chance of having a baby girl who is a carrier of haemophilia
• one in four chance of having a baby girl with haemophilia

This means it is possible for a female to have haemophilia, although it’s very rare.

No family history

In some cases, a boy is born with haemophilia even though there is no family history of the condition. In such cases it is thought the mutation developed spontaneously in the boy’s mother, grandmother or great-grandmother, but until then a male member of the family had never inherited the mutated gene.

Although family history is a strong indicator, some studies have shown that there is no known family history of haemophilia in up to one-third of new cases.

How haemophilia affects the blood

Blood cells called platelets are very important for blood clotting. These cells have a sticky surface that allows them to clump together to stop the flow of blood.

Platelets also need clotting factors. These are proteins that form a “web” around the platelets, helping them to stay in place.

The mutated haemophilia gene means that a child with the condition does not have enough clotting factors in their blood.

Several different clotting factors are present in the blood. They are numbered using roman numerals. For example, in haemophilia A there is not enough clotting factor VIII (8) in the blood. In haemophilia B there is not enough clotting factor IX (9) in the blood.

There are a number of problems someone with haemophilia may develop, and further treatment may be required.

Inhibitors

Inhibitors occur when the immune systems of people being treated with blood clotting factor medication start to regard clotting factors as foreign objects.

The immune system creates proteins called antibodies to block the affects of the clotting factor. These are known as inhibitors.

The inhibitors can make medication used to treat haemophilia less effective, which means it is more difficult to prevent and control bleeding.

An estimated 20-30% of people who have treatment for haemophilia A develop inhibitors, while around 1-3% of people who have treatment for haemophilia B develop inhibitors. They usually develop during the first year of treatment, but they can occur at any time.

Inhibitors are often temporary, but there are ways of managing the problem if it’s persistent.

Immune tolerance therapy (ITT)

People with moderate to severe inhibitors are usually advised to try a treatment programme called immune tolerance therapy (ITT).

ITT involves receiving daily injections of either octocog alfa (for haemophilia A) or nonacog alfa (for haemophilia B). Over time, the immune system should begin to recognise the blood clotting factors and stop producing inhibitors.

ITT is carried out on a long-term basis, with most people needing a course of treatment that lasts between 6 and 24 months. ITT is successful in an estimated 80% of cases.

Managing a bleed with inhibitors

In people with inhibitors the original clotting factors are removed, so in the event of a bleed a medication called a bypass agent must be used.

A bypass agent is a separate product that can be used to stop bleeding when inhibitors are still present. If ITT doesn’t work, you may need to use bypass agents for the rest of your life.

However, bypass agents can only be used as a response to a prolonged bleeding, not as preventative treatment.

Joint damage

Joint damage can sometimes develop if haemophilia is poorly controlled. Successive joint bleeds can damage cartilage (the soft spongy tissue in joints that acts as a shock absorber) as well as the synovium (a thin layer of tissue that lines the inside of the joint).

The more damaged a joint is, the more vulnerable it is to internal bleeding. This in turn means the joint will become even more damaged and vulnerable to bleeding.

Joint damage is more common in older adults with severe haemophilia because preventative treatments were not available in the past. It’s hoped that modern treatments mean children growing up with haemophilia today will not have joint damage.

Surgery can be used to treat joint damage. If the synovium is damaged, it can be removed so new synovium can grow in its place. If a joint is seriously damaged, it may be necessary to replace the whole joint with an artificial one, such as a hip replacement or knee replacement.

Several options are available to parents for the diagnosis of haemophilia before, during and after birth if there is a family history of the condition.

Tests before pregnancy

Genetic testing and counselling are available to help determine the risk of passing the condition onto a child.

This may involve testing a sample of your tissue or blood to look for signs of the genetic mutation that causes haemophilia.

Tests during pregnancy

If you become pregnant and have a history of haemophilia in your family, tests for the haemophilia gene can be carried out. These include:

• chorionic villus sampling (CVS) – a small sample of the placenta is removed from the womb and tested for the haemophilia gene, usually during weeks 10-13 of pregnancy
• amniocentesis – a sample of amniotic fluid is taken for testing, usually during weeks 15-20 of pregnancy

There is a small risk of these procedures causing problems such as miscarriage or premature labour, so you may want to discuss this with the doctor in charge of your care.

Tests after birth

If haemophilia is suspected after your child has been born, a blood test can usually confirm the diagnosis. The blood test will also be able to identify whether your child has haemophilia A or B, and how severe it is.

Read more about how a blood test is performed.

Haemophilia is an inherited condition that affects the blood’s ability to clot.

Normally, when you cut yourself substances in the blood known as clotting factors combine with blood cells called platelets to make the blood sticky. This makes the bleeding stop eventually.

However, in haemophilia there are not as many clotting factors as there should be in the blood. This means someone with the condition will bleed for longer than usual.

The condition is passed to a child by one or both of their parents.

Find out more about the causes of haemophilia.

How it affects you

The symptoms of haemophilia can be mild to severe depending on the level of clotting factors you have. Most cases are classified as severe.

People with severe haemophilia often experience internal bleeding. This usually occurs around the joints and muscles, causing pain and stiffness. It can also lead to joint damage over time.

Read more about the symptoms of haemophilia and the complications of haemophilia.

Types of haemophilia

The two most common types of haemophilia are haemophilia A and haemophilia B, although haemophilia A accounts for the majority of cases.

Both types have the same symptoms, but they are caused by problems with different clotting factors and have slightly different treatments.

There is also a rarer form of haemophilia called acquired haemophilia. This is not an inherited condition but is caused by the immune system (the body’s natural defence against infection and illness) attacking the clotting factors in the blood.

This section is about haemophilia A and B. See the Haemophilia Society website for more information about acquired haemophilia.

Who is affected?

There are about 6,000 people with haemophilia in the UK. Most of these are males because of the way the condition is inherited.

Worldwide, it is estimated that one boy in every 5,000 will be born with haemophilia A and one boy in every 30,000 will be born with haemophilia B.

However, females who carry the haemophilia gene may also experience some bleeding problems, such as heavy periods. There is also a chance that a girl could be born with haemophilia if both parents have the haemophilia gene.

If you have a family history of haemophilia, you can have tests before, during and after pregnancy to determine if your child has the condition.

Read more about diagnosing haemophilia.

Treating haemophilia

There is no cure for haemophilia. However, with treatment a person with the condition can usually enjoy a good quality of life.

In recent decades genetically engineered clotting factor medications have been developed to prevent and treat prolonged bleeding.

These medications are given as an injection, the timing of which depends on how severe the condition is. Injections are usually only given in milder cases in response to prolonged bleeding, whereas more severe cases are treated with regular injections to prevent bleeding.

Read more about treating haemophilia.

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The symptoms of haemophilia vary depending on how severe the condition is, but the main sign is prolonged bleeding.

The severity of the condition is determined by the level of clotting factors in the blood:

• mild haemophilia – where someone has between 5 and 50% of the normal amount of clotting factors
• moderate haemophilia – where someone has between 1 and 5% of the normal amount of clotting factors
• severe haemophilia – where someone has less than 1% of the normal amount of clotting factors

Most cases of haemophilia are severe.

Mild haemophilia

Children born with mild haemophilia may not have any symptoms for many years. The condition usually only becomes apparent after a significant wound, surgery, or a dental procedure such as having a tooth removed. These events could cause unusually prolonged bleeding.

Moderate haemophilia

As well as the above, children born with moderate haemophilia bruise easily. They may also have symptoms of internal bleeding around their joints, particularly if they have a knock or a fall that affects their joints. This is known as a joint bleed.

The symptoms usually begin with a tingling feeling of irritation and mild pain in the affected joint, most commonly the ankle joints, knee joints and elbow joints. Less commonly, the shoulder and hip joints can also be affected.

If a joint bleed is not treated, it can lead to:

• more severe joint pain
• stiffness
• the site of the bleed becoming hot, swollen and tender

Severe haemophilia

The symptoms of severe haemophilia are similar to those of moderate haemophilia. However, joint bleeding is more frequent and severe.

Children with severe haemophilia have spontaneous bleeding. This means that they start bleeding for no apparent reason. Spontaneous bleeding can take the form of nosebleeds, bleeding gums, joint bleeds and muscle bleeding.

Without treatment, people with severe haemophilia can develop:

• joint deformity, which may require replacement surgery
• soft tissue bleeding, which could lead to further complications
• serious internal bleeding

When to seek emergency medical help

There is a small risk of bleeding inside the skull, known as an intracranial haemorrhage. It is estimated that 3% of people with moderate or severe haemophilia will have an intracranial haemorrhage. However, spontaneous bleeding inside the skull is uncommon and is usually only caused by a head injury.

Bleeding in the skull should be treated as a medical emergency.

The symptoms of an intracranial haemorrhage include:

• severe headache
• stiff neck
• vomiting
• a change in mental state, such as confusion
• speaking difficulties, such as slurred speech
• changes in vision, such as double vision
• loss of co-ordination and balance
• paralysis of some or all of the facial muscles

Call 999 for an ambulance if you think that you or your child has bleeding inside the skull.

If your child is diagnosed with haemophilia, their recommended treatment plan will depend on how severe their haemophilia is.

There are two main approaches to treatment:

• preventative treatment – where medication is used to prevent episodes of bleeding and subsequent joint and muscle damage
• on-demand treatment – where medication is used in response to an episode of prolonged bleeding

You will usually be treated by a team of healthcare professionals at a specialist haemophilia hospital department.

Preventative treatment

Most cases of haemophilia are severe and require preventative treatment (prophylaxis). This involves regular injections of clotting factor medication.

When your child is young, you will be trained to give them the injections. They will be taught how to inject themselves when they are older. This will avoid the need for regular hospital appointments.

In some cases, injections may be given into a device called an implantable port, which can be surgically placed under the skin. This port is connected to a blood vessel near the heart, meaning you don’t need to try to find a vein for every injection.

If you’re having preventative treatment, you’ll need regular follow-up appointments with your care team so your progress can be monitored.

Preventative treatment is usually continued until you’re fully grown. After this point it may be possible to change to on-demand treatment, but you may be advised to switch back to preventative treatment if you experience any episodes of significant bleeding.

Haemophilia A

Preventative treatment for haemophilia A involves regular injections of a medication called octocog alfa. This is an engineered version of clotting factor VIII (8), the clotting factor that people with haemophilia A don’t have enough of. Injections every 48 hours are often recommended.

Common side effects of octocog alfa include an itchy skin rash and redness and soreness at the site of the injection.

Haemophilia B

Preventative treatment for people with haemophilia B involves regular injections of a medication called nonacog alfa. This is an engineered version of clotting factor IX (9), which people with haemophilia B don’t have enough of. Injections twice a week are often recommended.

Side effects of nonacog alfa are uncommon, but include headaches, altered taste, nausea, and discomfort and swelling at the injection site.

On-demand treatment

In mild or moderate cases, treatment for haemophilia may only be necessary as an immediate response to bleeding.

Haemophilia A

People with haemophilia A can be treated on-demand with injections of octocog alfa or a medication called desmopressin.

Desmopressin is a synthetic hormone. Hormones are powerful chemicals that can have a wide range of effects on the body. Desmopressin works by stimulating the production of clotting factor VIII (8) and is usually given by injection.

Possible side effects of desmopressin include headache, stomach pain and nausea.

Haemophilia B

On-demand treatment for haemophilia usually involves injections of a medication called nonacog alfa.

For more information about these medications, see haemophilia medicines information.

Living with haemophilia

With treatment, most people with haemophilia can live a normal life. However, there are some things you’ll need to be careful of.

For example, you should avoid contact sports such as rugby. You also need to be careful taking other medications because some medicines can interfere with your blood’s ability to clot. Common examples of these include aspirin and ibuprofen.

The team caring for you will be able to offer further information and advice about living with haemophilia.