Novel Likely Pathogenic Variant in the A3 Domain of von Willebrand Factor Leading to a Collagen-Binding Defect.

Von Willebrand disease (VWD) is the most prevalent congenital bleeding disorder. Diagnosis and classification of VWD is complex due to its heterogeneity regarding clinical manifestations and molecular genetic analysis. Genetic investigations became an inherent part of diagnosis and help distinguish different types/subtypes of VWD. Although many variants have been listed being causative for VWD, the genetic etiology remains undefined in a lot of patients. We report about two siblings with severely reduced values for von Willebrand factor collagen-binding activity (VWF:CB). Genetic analysis using panel sequencing identified a heterozygous non-synonymous single nucleotide variant in exon 30. At the protein level, the alteration (p.Ser1731Leu) is located in the A3 collagen-binding domain. The amino acid position is already known to be important for collagen binding because p.Ser1731Thr has been reported to affect the VWF:CB.