(A) Crystal structure of B domain-deleted factor VIII (PDB ID 2R7E). The domains are individually labeled and in different colors. The positions of the mutations studied in this article are indicated by arrows. Close-up views of the positions of the mutations with the mutated and nearby residues shown as stick models and hydrogen bonds as dashed lines. (B) The p.G520(539)R mutation located in the interface between the A1 and A2 domains and (C) the p.C179(198)R mutation located in A2 domain.