Hemophilia is a rare bleeding disorder in which a protein needed for proper blood clotting is missing or at a low level. Types include hemophilia A — low or no clotting factor 8 (VIII); hemophilia B — low or no clotting factor 9 (IX); and hemophilia C — low or no clotting factor 11 (XI). Hemophilia A is the most common type. Bleeding disorders can be mild, moderate or severe.
Hemophilia A or B almost always occurs in boys and is passed from mother to son through a gene. The gene that causes hemophilia C can be passed on to both boys and girls by either parent. Although usually inherited, in some cases hemophilia is caused by a change in the person's own gene (spontaneous gene mutation) rather than a parent's gene. Rarely, hemophilia develops later in life (acquired hemophilia) from an immune system problem that usually gets better with proper treatment. Most people can live fairly normal lives by receiving regular infusions of whichever clotting factor is low or missing.
Signs and symptoms of hemophilia vary, depending on the severity, but may include bleeding for a long time after an injury, many large or deep bruises, internal bleeding that can damage organs and tissues, and other symptoms. Females who have the affected gene (carriers of the disease) can have symptoms if their clotting factors are below the normal range. Carriers can also have heavy menstrual periods and excessive postpartum bleeding.
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