Deficiency or dysfunction of FIX leads to hemophilia B (HB), an X-linked, recessive, bleeding disorder. On a molecular basis, HB is due to a heterogeneous spectrum of mutations spread throughout the F9 gene (Rallapalli PM et al. 2013).
The Reactome event describes the defective proteolytic activation of FIX by factor XIa due to the presence of HB-associated point mutations R191C, R191H, R226Q and R226W in the cleavage sites of FIX (Liddell MB et al. 1989; Monroe DM et al. 1989; Suehiro K et al. 1989; Diuguid DL et al. 1989; Bertina RM et al.1990). In addition, naturally occurring point mutations in the FIX propeptide sequence such as N43Q, N43L or N46S are also annotated here. These FIX variants are secreted into the circulation with a mutant 18-amino acid propeptide still attached (Bentley AK et al. 1986; Galeffi P & Brownlee GG 1987). The unprocessed FIX variants were found to affect the function of the protein by destabilizing the calcium-induced conformation of FIX (Wojcik EG et al. 1997) and showed delayed activation by FXIa (Liddell MB et al. 1989; Ware J et al. 1989; de la Salle C et al. 1993; Wojcik EG et al. 1997; Bristol JA et al. 1993).