What is "haemophilia"

n. (context British spelling pathology English) Any of several hereditary illnesses that impair the body's ability to control bleeding, usually passed from mother to son.

n. congenital tendency to uncontrolled bleeding; usually affects males and is transmitted from mother to son [syn: hemophilia, bleeder's disease]

Haemophilia also spelled hemophilia, is a mostly inherited, genetic disorder that impairs the body's ability to form blood clots, a process needed to stop bleeding when a blood vessel is broken. There are two main types, haemophilia A and haemophilia B. Haemophilia A is due to a deficiency in clotting factor VIII and is the most common type, present in about 1 in 5,000–10,000 male births. Haemophilia B is due to a deficiency in factor IX and occurs in around 1 in about 20,000–34,000 male births. A third type haemophilia C due to a deficiency in factor XI, is a rare, mild form that can affect both sexes. This type is mostly found in Ashkenazi Jews and rarely in other population groups.

Another mild and rare form of haemophilia is known as parahaemophilia and is due to a deficiency in factor V, which can be inherited or acquired. A non-genetic form of haemophilia is caused by autoantibodies against factor VIII and so is known as acquired haemophilia A. Acquired haemophilia can be associated with cancers, autoimmune disorders and following childbirth.

Like other X-linked recessive disorders, haemophilia A and B are more likely to occur in males than females. This is because females have two X chromosomes while males have only one, so the defective gene is guaranteed to manifest in any male who carries it. Because females have two X chromosomes and haemophilia is rare, the chance of a female having two defective copies of the gene is very remote, so females are almost exclusively asymptomatic carriers of the disorder. Female carriers can inherit the defective gene from either their mother or father, or it may be a new mutation. Although it is not impossible for a female to have haemophilia, it is unusual: daughters which are the product of both a male with haemophilia A or B and a female carrier will possess a 50% chance of having haemophilia, and if the daughter does not have hemophilia, she will carry it.

People with haemophilia have lower clotting factor level of blood plasma or impaired activity of the coagulation factors needed for a normal clotting process. Thus when a blood vessel is injured, a temporary scab does form, but the missing coagulation factors prevent fibrin formation, which is necessary to maintain the blood clot. A haemophiliac does not bleed more intensely than a person without it, but can bleed for a much longer time. In severe cases even a minor injury can result in blood loss lasting days or weeks, or even never healing completely. In areas such as the brain or inside joints, this can be fatal or permanently debilitating. The word is from the Greek haima αἷμα 'blood' and philia φιλία 'love'.