Description
Factor VIII is a large glycoprotein (320 kDa) synthesized in the liver. The majority of Factor VIII is cleaved during expression, resulting in a mixture of partially cleaved forms ranging in size from 200-280 kDa. The F.VIII is stabilized in circulation through non-covalent association with von Willebrand Factor. The concentration of F.VIII in normal human plasma is typically 200 ng/mL. In canine plasma, the F.VIII activity is 5-7 fold higher relative to human plasma. F.VIII is a pro-cofactor that is activated through limited proteolysis by thrombin. In this process F.VIIIa dissociates from vWF to combine with activated Factor IX, calcium and a phospholipid surface where it is an essential cofactor in the assembly of the Factor X activator complex. Hemophilia A is a congenital bleeding disorder resulting from an X-chromosome-linked deficiency of F.VIII, occurring with a frequency of 1 in 4000 males. The defect can be caused by any one of hundreds of reported mutations but are most commonly due to inversions within intron 22 of the F.VIII gene. Hemophilia A has also been reported in a variety of species including dog and mouse, with a clinical phenotype very similar to human. The genetic defect in one case of canine Hemophilia-A has been shown to also be due to a gene inversion similar to the human defect, possibly indicating a common instability of the F.VIII gene in humans and dogs