The number of rare nonsynonymous VWF variants is significantly associated with VWF:Ag levels, regardless of VWD type.
VWF sequence alone will not reveal the cause of VWD in a majority of patients with higher VWF:Ag levels.
Approximately 35% of patients with Type 1 von Willebrand Disease (VWD) do not have a known pathogenic variant in the VWF gene. We aimed to understand the impact of coding variants in VWF on VWD risk and VWF antigen (VWF:Ag) levels. 527 Low VWF and VWD patients and 210 healthy controls were studied. VWF sequencing was performed and VWF:Ag levels assayed. CADD (Combined Annotation Dependent Depletion) score >20 was used as a measure of predicted pathogenicity. The number of rare nonsynonymous VWF variants significantly predicted VWF:Ag levels (p=1.62x10-21). There was an association between average number of rare nonsynonymous VWF variants with VWD Type 1 (p=2.4x10-13) and Low VWF (p=1.6x10-27) compared to normal subjects, with Type 1 subjects possessing on average >2 times as many rare variants as those with Low VWF and eight times as many as normal subjects. The number of rare nonsynonymous variants significantly predicts VWF:Ag levels even after controlling for presence of a variant with CADD score > 20 or a known pathogenic variant in VWF (p=2.7x10-14). The number of rare nonsynonymous variants in VWF as well as the presence of a variant with CADD >20 are both significantly associated with VWF levels. The association with rare nonsynonymous variants holds even when controlling for known pathogenic variants, suggesting that additional variants, both in VWF or elsewhere, are also associated with VWF:Ag levels. Patients with higher VWF:Ag levels who have fewer rare nonsynonymous variants in the VWF gene could benefit from next-generation sequencing to find the cause of their bleeding.