Importance of Genotyping in von Willebrand Disease to Elucidate Pathogenic Mechanisms and Variability in Phenotype

Abstract

Genotyping is not routinely performed at diagnosis of von Willebrand disease (VWD). Therefore, the association between genetic variants and pathogenic mechanism or the clinical and laboratory phenotype is unknown in most patients, especially in type 1 VWD. To investigate whether genotyping adds to a better understanding of the pathogenic mechanisms and variability in phenotype, we analyzed the VWF gene in 390 well-defined VWD patients, included in the WiN study. A VWF gene variant was found in 155 patients (61.5%) with type 1, 122 patients (98.4%) with type 2, and 14 patients (100%) with type 3 VWD. Forty-eight variants were novel. For each VWF gene variant, the pathogenic mechanisms associated with reduced VWF levels was investigated using the FVIII:C/VWF:Ag and VWFpp/VWF:Ag ratios. In type 1 VWD, reduced synthesis or secretion of VWF was most frequently found in patients with nonsense variants, frameshift variants, and deletions, whereas rapid clearance of VWF was mainly found in patients with missense variants. Furthermore, type 1 VWD patients with and without a VWF gene variant were clearly distinct in their clinical features such as age of diagnosis, laboratory phenotype, and bleeding phenotype. In type 2 VWD, 81% of variants were associated with an increased clearance of VWF. To conclude, we identified the pathogenic mechanisms associated with various VWF gene variants in type 1, 2, and 3 VWD patients. Additionally, major differences in the phenotype of type 1 VWD patients with and without a variant were observed, which may be of importance for clinical management.

Clinical and Laboratory Presentation and Underlying Mechanism in Patients with Low VWF

“…It has also been suggested that type 1 VWD should be diagnosed only in patients with significantly decreased VWF levels and frequent bleeding, to reduce the risk of diagnosing with an inherited hemorrhagic disease a number of healthy people. 18 Following this criterion, several large genetic studies on VWD type 1 showed that pathogenic VWF variants are often identified in patients with VWF levels <30 IU/dL, [19][20][21][22] whereas only approximately 40 to 50% of those with levels of 30 to 50 IU/dL have a pathogenic VWF variant. 8,9 Despite these comprehensive investigations of type 1 VWD, cases with low VWF received less attention.…”

“…18 . Following this criterion, several large genetic studies on VWD type 1 showed that pathogenic VWF variants are often identified in patients with VWF levels <30 IU/dL[19][20][21][22] , whereas only approximately 40-50% of those with levels of 30-50 IU/dL have a pathogenic VWF variant8,9 . Despite these comprehensive investigations of type 1 VWD, cases with low VWF received less attention.…”

Type 1 VWD classification revisited: novel insights from combined analysis of the LoVIC and WiN studies

“…The genetic analysis in the WiN and LoVIC studies have previously been described. 14 , 19 In short, in the LoVIC study a custom genetic array was used to sequence VWF . TruSeq Custom Amplicon v1.5 Library Prep Kit (Illumina, San Diego, CA) was used to prepare the libraries.…”

“… 7 , 8 , 9 , 10 For example, VWF pathological sequence variants were significantly more prevalent in patients with plasma VWF levels <30 IU/dL than in those with low VWF. 11 , 12 , 13 , 14 , 15 In addition, mucocutaneous bleeding in the type 1 VWD group was more common and correlated inversely with residual plasma VWF levels. 11 , 16 Conversely, accumulating data have demonstrated that many individuals with mild-to-moderate reduction of plasma VWF levels in the 30 to 50 IU/dL range do not have significant bleeding tendencies.…”