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Haemophilia, also spelled hemophilia, is a group of hereditary genetic disorders that impairs the body's ability to control blood clotting, which is used to stop bleeding when a blood vessel is broken. Haemophilia A (clotting factor VIII deficiency) is the most common form of the disorder, present in about 1 in 5,000–10,000 male births.〔(【引用サイトリンク】title=Hemophilia B )〕 Haemophilia B (factor IX deficiency) occurs in around 1 in about 20,000–34,000 male births. Like other recessive sex-linked, X chromosome disorders, haemophilia is 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 have haemophilia, while the non-sex-linked haemophilia C due to coagulant factor XI deficiency, which can affect either sex, is more common in Jews of Ashkenazi (east European) descent but rare in other population groups. 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 haemophiliacs 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'.〔(【引用サイトリンク】title=Online Etymology Dictionary )〕 == Signs and symptoms == Characteristic symptoms vary with severity. In general symptoms are internal or external bleeding episodes, which are called "bleeds".〔(Types of Bleeds ) National Hemophilia Federation.〕〔(Key facts: what is haemophilia? ) The Haemophilia Society.〕 People with more severe haemophilia suffer more severe and more frequent bleeds, while people with mild haemophilia usually suffer more minor symptoms except after surgery or serious trauma. Moderate haemophiliacs have variable symptoms which manifest along a spectrum between severe and mild forms. In both haemophilia A and B, there is spontaneous bleeding but a normal bleeding time, normal prothrombin time, normal thrombin time, but prolonged partial thromboplastin time. Internal bleeding is common in people with severe haemophilia and some individuals with moderate haemophilia. The most characteristic type of internal bleed is a joint bleed where blood enters into the joint spaces.〔 This is most common with severe haemophiliacs and can occur spontaneously (without evident trauma). If not treated promptly, joint bleeds can lead to permanent joint damage and disfigurement.〔 Bleeding into soft tissues such as muscles and subcutaneous tissues is less severe but can lead to damage and requires treatment. Children with mild to moderate haemophilia may not have any signs or symptoms at birth especially if they do not undergo circumcision. Their first symptoms are often frequent and large bruises and haematomas from frequent bumps and falls as they learn to walk. Swelling and bruising from bleeding in the joints, soft tissue, and muscles may also occur. Children with mild haemophilia may not have noticeable symptoms for many years. Often, the first sign in very mild haemophiliacs is heavy bleeding from a dental procedure, an accident, or surgery. Females who are carriers usually have enough clotting factors from their one normal gene to prevent serious bleeding problems, though some may present as mild haemophiliacs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Haemophilia」の詳細全文を読む スポンサード リンク
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