Factor VIII is an essential blood-clotting protein, also known as anti-hemophilic factor. In humans, factor VIII is encoded by the F8 gene. Defects in this gene result in hemophilia A, a recessive X-linked coagulation disorder.

Hemophilia type A is a rare genetic disorder caused by missing or defective factor VIII (FVIII), a clotting protein in the blood. The disease is usually inherited, but in about one-third of known cases, it is caused by a spontaneous mutation.