The NM_000552.5:c.4010C>T variant in VWF is a missense variant predicted to cause substitution of proline by leucine at amino acid 1377 (p.Pro1377Leu). At least 1 patient with this variant displayed excessive mucocutaneous bleeding as well as a laboratory phenotype of enhanced RIPA and loss of HMWM, which is specific for VWD type 2B. (PP4, PMID 1373334). This variant has been reported in 1 additional proband meeting VWD 2B PP4 laboratory phenotype of enhanced RIPA (PS4_Supporting; Gold Variant Database). The Grpmax filtering allele frequency in gnomAD v4.1 is 0.00000183 (based on 6/1179864 alleles in the European non-Finnish population), which is lower than the ClinGen VWD VCEP threshold of <0.0001 for type 2B (PM2_Supporting). Platelet binding assay performed with the p.Pro1377Leu recombinant mutant vWF expressed by COS-7 showed increased binding at low doses of ristocetin, indicating that this variant has a gain of function effect on the protein (PMID 1373334)(PS3_supporting). In summary, this variant meets the criteria to be classified as likely pathogenic for autosomal dominant von Willebrand disease type 2B based on the ACMG/AMP criteria applied, as specified by the ClinGen VWD VCEP: PP4, PS4_Supporting, PM2_Supporting, PS3 (ClinGen von Willebrand Disease Expert Panel Specifications to the ACMG/AMP Variant Interpretation Guidelines for VWF Version 1.0.0)