Unraveling the molecular basis underlying nine putative splice site variants of von Willebrand factor

Approximately 10% of von Willebrand factor (VWF) gene variants are suspected to disrupt messenger RNA (mRNA) processing, the number of which might be underestimated due to the lack of transcript assays. In the present study, we provided a detailed strategy to evaluate the effects of nine putative splice site variants (PSSVs) of VWF on mRNA processing as well as protein properties and establish their genotype-phenotype relationships. Eight of nine PSSVs affected VWF splicing: c.322AT, c.1534-13_1551delinsCA, and c.8116-2del caused exon skipping; c.221-2AC, c.323+1GT, and c.2547-13TA resulted in the activation of cryptic splice sites; c.2684AG led to exon skipping and activation of a cryptic splice site; c.2968-14AG created a new splice site. The remaining c.5171-9del was likely benign. The efficiency of nonsense-mediated mRNA decay (NMD) was much higher in platelets compared to leukocytes, impairing the identification of aberrant transcripts in 4 of 8 PSSVs. The nonsense variant c.322AT partially impaired mRNA processing, leaking a small amount of correct transcripts with c.322T (p.Arg108*), while the missense variant c.2684AG totally disrupted normal splicing of VWF, rather than produced mutant protein with the substitution of Gln895Arg. The results of this study would certainly add novel insights into the molecular events behind von Willebrand disease.