Haemophilia is a rare bleeding disorder. The condition affects the blood's ability to clot, meaning that people with haemophilia bleed more easily than other people.1 In the UK, around one in 2,000 men, women and children have a diagnosed bleeding disorder such as haemophilia.2 Bleeding disorders are typically passed down from parent to child, but about a third of cases have no known family history and can be the result of a random gene mutation.2
There are two different types of the haemophilia, haemophilia A and haemophilia B. In both types, the body does not produce enough of a protein, called clotting factor, that helps the blood to clot.1
- Haemophilia A is the most common type, affecting around one in 5,000 males. It is caused by a lack of clotting factor VIII.3
- Haemophilia B is less common, affecting around one in 30,000 males. It is caused by a lack of clotting factor IX.3
Haemophilia is caused by a change to the genes responsible for producing clotting factors VIII and IX, which are carried on the X chromosome.3 Because females have two copies of the X chromosome and males have one X chromosome and one Y chromosome, the condition affects them differently.3 If a female carries an altered haemophilia gene on just one of her two X chromosomes, then she is known as a carrier.3 While female carriers may have symptoms of haemophilia, these are usually milder and less common than in males.1 If a male receives an altered haemophilia gene on his X chromosome, then he will be affected with haemophilia.3
In severe cases of haemophilia, continuous bleeding can occur after minor trauma or even in the absence of injury (known as spontaneous bleeding).4 Internal bleeding into joints and muscles also affects people with severe haemophilia. This can cause swelling and pain.3,4 Over time, repeated bleeding can result in permanent damage to affected areas.3
Bleeding can be controlled by replacing the missing clotting factors in the blood.3 Treatment is given as injections, either when a bleed occurs (on-demand therapy), or on a regular basis (prophylactic treatment) to prevent bleeds from occurring in the first place.3
Over the last fifty years, treatment innovations have dramatically transformed the outlook for people living with haemophilia, such that life expectancy is now close to that of the general population in high income countries.4
We are continuing to drive change for a future where everyone living with haemophilia and other rare bleeding disorders can get the treatment they need and live a life with as few limitations as possible.
Our scientists are exploring innovative treatment solutions for haemophilia and rare blood disorders with the aim of reducing the existing unmet needs, as well as improving clinical outcomes.
We strive to offer better quality of life to people living with haemophilia and other rare bleeding disorders.
AH differs from haemophilia A and B because it’s not inherited.6 Instead, AH develops later in life in people with no personal or family history of bleeding disorders.6,7 AH is very rare and occurs when the immune system develops antibodies against its own clotting factor, most frequently factor VIII.7
Bernard-Soulier syndrome is a very rare platelet function disorder, with around 96 people diagnosed with the condition in the UK. It is caused by defects in a group of proteins, known as a receptor, found on the surface of platelets, a type of blood cell. When this receptor is missing or not functioning correctly, platelets are unable to stick to the injured blood vessel wall, preventing the blood from clotting properly. Bernard-Soulier syndrome is inherited from both parents and affects males and females equally.8
In factor I deficiency a person has problems with a protein called fibrinogen, or factor I, which is needed for the blood to clot. It occurs because the body does not produce enough, or because the factor I that is produced does not work properly. There are several different types of factor I bleeding disorders, all of which affect males and females equally.9
Afibrinogenaemia
Afibrinogenaemia is caused when the body does not produce any factor I. It is a rare condition, affecting around one in a million people globally.9
Dysfibrinogenaemia
Dysfibrinogenaemia is caused when a person has normal levels of factor I, but it does not work properly. It can be inherited or can develop as a result of other diseases, which is more common.9
Hypofibrinogenaemia
Hypofibrinogenaemia occurs when the body does not produce enough factor I. It is a rare condition.9
Factor II deficiency is caused by problems with factor II (prothrombin), a protein needed for blood to clot. It occurs either because the body does not produce enough factor II, or because the factor II produced does not work properly. Factor II deficiency is an extremely rare condition, affecting around one in every two million people globally. It can either be inherited from both parents, or it is also possible to develop a factor II deficiency later in life – this is called acquired factor II deficiency.9
Factor V deficiency is caused by the body not producing enough factor V, a protein needed for the blood to clot. It is a very rare condition, affecting around one in a million people globally. It is inherited from both parents, but can also develop later in life. It affects both males and females equally.9
Factor VII deficiency is caused by the body not producing enough factor VII, a protein needed for the blood to clot. It is one of the most common rare bleeding disorders. It is inherited from both parents, but can also develop later in life. It affects males and females equally, although women are more likely to have symptoms.9
In factor X deficiency the body does not produce enough factor X, a protein needed for the blood to clot. It is a rare condition, affecting an estimated one in a million people globally. Factor X deficiency is usually inherited from both parents, but it can also develop later in life. It affects males and females equally.9
Factor XI deficiency is caused by the body not producing enough factor XI, a protein needed for the blood to clot. It is a rare condition, affecting around one in a million people globally. However, it is much more common in some populations, including the Ashkenazi Jewish community, affecting up to one in 450 people. It is inherited from both parents, but can also develop later in life, and it affects both males and females equally.9
Factor XIII deficiency is caused by the body not producing enough factor XIII, a protein needed for the blood to clot. It affects approximately one in every two million people globally, making it one of the rarest bleeding disorders. It is inherited from both parents, although it can develop later in life. The condition affects both males and females equally.9
Glanzmann’s thrombasthenia is a rare platelet disorder caused by a defect in glycoproteins IIb/IIIa, which prevent the platelets from sticking together to form a stable clot. This means the blood is unable to clot properly. It is very rare, affecting one in million people globally, with around 149 diagnosed cases in the UK. It is inherited from both parents, but in very rare circumstances it can develop later in life. It affects both males and females equally.10
Platelets require granules to form a plug and stop bleeding. In platelet storage pool deficiency, the granules don’t work properly, and platelets cannot form a plug to stop bleeding. This disorder is usually inherited from one or both parents and occurs in both men and women.
Sickle cell disease is a group of disorders caused by defects in haemoglobin, the protein inside red blood cells that carries oxygen around the body.11,12 In sickle cell disease, the haemoglobin is abnormally shaped which can lead to the red blood cells getting stuck in small blood vessels and blocking blood flow.12 Sickle cell disease is inherited from both parents.12 It is estimated to affect around 17,500 people in the UK.13
von Willebrand disease is caused by problems with von Willebrand factor (VWF), a protein needed for the blood to clot. It occurs either because the body does not produce enough VWF, or because the VWF produced doesn’t work properly, or both. It is the most common inherited bleeding disorder, affecting more than 11,000 people in the UK. Although it affects males and females equally, women tend to show more symptoms due to menstruation and childbirth.14
NHS UK. Haemophilia; 9 January 2025. Available from: https://www.nhs.uk/conditions/haemophilia/ [Accessed March 2026]
The Haemophilia Society. Bleeding disorders. Available from: https://haemophilia.org.uk/bleeding-disorders/ [Accessed March 2026]
The Haemophilia Society. Understanding haemophilia; 2023. Available from: https://haemophilia.org.uk/wp-content/uploads/2023/07/THS_A5_understanding_JCv1_interactive.pdf [Accessed March 2026]
Mehta P and Reddivari AKR. Hemophilia; 5 Jun 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551607/ [Accessed March 2026]
Khair K et al. Prevalence and perceptions of pain in people with haemophilia: A UK study. Haemophilia. 2023;29(6):1509-1518; doi: 10.1111/hae.14860
The Haemophilia Society. How do you get haemophilia? Available from: https://haemophilia.org.uk/bleeding-disorders/faqs/how-do-you-get-haemophilia/ [Accessed March 2026]
Guy’s and St Thomas’ NHS Foundation Trust. Bleeding disorders; June 2024. Available from: https://www.guysandstthomas.nhs.uk/health-information/bleeding-disorders [Accessed March 2026]
The Haemophilia Society. Bernard-Soulier syndrome factsheet. Available from: https://haemophilia.org.uk/wp-content/uploads/pdf/factsheet_BS-1.pdf [Accessed March 2026]
The Haemophilia Society. Rare bleeding disorders; 2023. Available from: https://haemophilia.org.uk/resources/publications/booklets/rare-bleeding-disorders/ [Accessed March 2026]
The Haemophilia Society. Glanzmann’s thrombasthenia factsheet. Available from: https://haemophilia.org.uk/wp-content/uploads/pdf/factsheet_glanz.pdf [Accessed March 2026]
NHS UK. Sickle cell disease; 30 November 2022. Available from: https://www.nhs.uk/conditions/sickle-cell-disease/ [Accessed March 2026]
NHS UK. Sickle cell disease – Causes; 30 November 2022. Available from: https://www.nhs.uk/conditions/sickle-cell-disease/causes/ [Accessed March 2026]
Sickle Cell Society. About sickle cell. Available from: https://www.sicklecellsociety.org/about-sickle-cell/ [Accessed March 2026]
The Haemophilia Society. Understanding VWD; April 2022. Available from: https://haemophilia.org.uk/wp-content/uploads/2022/09/THS_A5_Booklet_VWD_April_2022.pdf [Accessed March 2026]