Haemophilia

Haemophilia
Other names	Hemophilia
A drawing of clotting factor VIII
Pronunciation	/hiːməˈfɪliə/
Specialty	Haematology
Symptoms	Easy and prolonged bleeding[1]
Usual onset	At birth[2]
Causes	Usually genetic[3]
Diagnostic method	Blood test[4]
Prevention	Preimplantation screening[4]
Treatment	Replace missing blood clotting factors[3]
Frequency	1 in 7,500 males (haemophilia A), 1 in 40,000 males (haemophilia B)[2][5]

Haemophilia (British English), or hemophilia (American English)^[6] (from Ancient Greek αἷμα (haîma) 'blood' and φιλία (philía) 'love of'),^[7] is a mostly inherited genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding.^[2][3] This results in people bleeding for a longer time after an injury, easy bruising, and an increased risk of bleeding inside joints or the brain.^[1] Those with a mild case of the disease may have symptoms only after an accident or during surgery.^[1] Bleeding into a joint can result in permanent damage while bleeding in the brain can result in long term headaches, seizures, or an altered level of consciousness.^[1]

There are two main types of haemophilia: haemophilia A, which occurs due to low amounts of clotting factor VIII, and haemophilia B, which occurs due to low levels of clotting factor IX.^[2] They are typically inherited from one's parents through an X chromosome carrying a nonfunctional gene.^[8] Most commonly found in men, haemophilia can affect women too, though very rarely. A woman would need to inherit two affected X chromosomes to be affected, whereas a man would only need one X chromosome affected. It is possible for a new mutation to occur during early development, or haemophilia may develop later in life due to antibodies forming against a clotting factor.^[2][8] Other types include haemophilia C, which occurs due to low levels of factor XI, Von Willebrand disease, which occurs due to low levels of a substance called von Willebrand factor, and parahaemophilia, which occurs due to low levels of factor V.^[9][10] Haemophilia A, B, and C prevent the intrinsic pathway from functioning properly; this clotting pathway is necessary when there is damage to the endothelium of a blood vessel.^[11][12][13] Acquired haemophilia is associated with cancers, autoimmune disorders, and pregnancy.^[14][15] Diagnosis is by testing the blood for its ability to clot and its levels of clotting factors.^[4]

Prevention may occur by removing an egg, fertilising it, and testing the embryo before transferring it to the uterus.^[4] Human embryos in research can be regarded as the technical object/process. Missing blood clotting factors are replaced to treat haemophilia.^[3] This may be done on a regular basis or during bleeding episodes.^[3] Replacement may take place at home or in hospital.^[16] The clotting factors are made either from human blood or by recombinant methods.^[16] Up to 20% of people develop antibodies to the clotting factors which makes treatment more difficult.^[3] The medication desmopressin may be used in those with mild haemophilia A.^[16] Studies of gene therapy are in early human trials.^[17]

Haemophilia A affects about 1 in 5,000–10,000, while haemophilia B affects about 1 in 40,000 males at birth.^[2][5] As haemophilia A and B are both X-linked recessive disorders, females are rarely severely affected.^[8] Some females with a nonfunctional gene on one of the X chromosomes may be mildly symptomatic.^[8] Haemophilia C occurs equally in both sexes and is mostly found in Ashkenazi Jews.^[5] In the 1800s haemophilia B was common within the royal families of Europe.^[5] The difference between haemophilia A and B was determined in 1952.^[5]