The p. Arg1800His Mutation of Factor VIII Results in Moderate Hemophilia A Due to Defective Processing and Stability of Functional Protein.

Haemophilia A (HA) is a rare congenital, recessive X-linked bleeding disorders caused by the lack or deficiency of clotting factor VIII (FVIII). Missense variants, which can alter protein structure, conformation and immunogenicity, are found in nearly all individuals with mild or moderate hemophilia A but in fewer than 20% of those with the severe form. Here, we identified a 26-year-old man with a hemizygous F8 mutation (NM_000132.4(F8):c.5399 G > A (p. Arg1800His)) through direct sequencing of all exons of the F8 gene, which is established to cause a lack of FVIII:c (%) in circulating blood and leads to moderate HA. In addition, we also provide evidence for the reduced active FVIII (FVIII:c (%)) caused by p. Arg1800His mutation. In detail, we show that p. Arg1800His mutation may activate the unfolded protein response through IRE1a-XBP1 pathway and reduce stability of FVIII. Results from co-immunoprecipitation assays showed that p. Arg1800His mutation decreases the interaction between FVIII and PDIA5. Furthermore, unbiased molecular dynamics simulations highlight the importance of Arg1800 in the interactions FVIII and von Willebrand factor. These findings demonstrate the crucial role of Arg1800 in the correct biogenesis of FVIII and shed light on molecular mechanisms through which missense mutations in FVIII contribute to the development of moderate hemophilia A.