Hemophilia (from Greek "heme" meaning "blood", and "philia" meaning "love" are hereditary genetic disorders that impair ability to control blood clotting, which is used to stop bleeding.

• Hemophilia A (aka clotting factor VIII deficiency), the most common. Factor VIII (aka anti-hemophilic factor) is produced in the liver and throughout the body, circulating blood in it's inactive form bound to von Willebrand factor, until an injury that damages blood vessels, where factor VIII breaks from von Willebrand factor. The activated protein, called coagulation factor VIIIa, interacts with coagulation factor IX, to set off a chain of reactions to form a clot
• Hemophilia B (aka clotting factor IX deficiency), the next most common
• Hemophilia C (aka coagulant factor XI deficiency)

• Hemophilia Pt's have lower clotting factor level of blood plasma, or impaired activity of the coagulation factors needed for a normal clotting process
• When a blood vessel is injured, a temporary scab forms, but the missing coagulation factors prevent fibrin formation, which is necessary to maintain the blood clot

• Hemophiliac doesn't bleed more intensively than a person without it, but can bleed for a much longer time
• In severe hemophiliacs, even a minor injury can result in blood loss lasting days to weeks, or even never healing completely. In areas such as the brain or inside joints, this can be fatal or permanently debilitating

• Like most recessive sex-linked X chromosome disorders, it is more likely to occur in males than females, because females have 2 X chromosomes (cf. males who have only 1), so females have a spare copy
• The chance of females having 2 defective copies of the gene is very remote, so females are almost exclusively asymptomatic carriers of the disorder
• Females can inherit the defective gene from the mother or father, or it may be a new mutation
• Hemophilia A is the most common form, present in 1 in 7.5k male births
• Hemophilia B occurs in 1 in 27k male births
• Non-sex-linked hemophilia C, which can affect either sex, is more common in Jews, but rare in other population groups

• von Willebrand disorder