A novel von Willebrand factor mutation (I1372S) associated with type 2B-like von Willebrand disease: An elusive phenotype and a difficult diagnosis

Abstract

SummaryMutations in the A1 domain of von Willebrand factor (VWF) may be associated with gain of function in theVWF-platelet GPIb interaction and consumption of largeVWF multimers, as seen in type 2B von Willebrand disease (VWD). We report a new VWF abnormality associated with greater VWF-GPIb interaction in the presence of all VWF multimers. The index case is a woman with a lifelong history of bleeding, found hyperresponsive to ristocetin with spontaneous platelet aggregation (SPA). She had normal factor VIII,VWF:Ag,VWF:RCo and VWF:CB levels, normal VWF:RCo/VWF:Ag and VWF:CB/VWF:Ag ratios, and a full panel of plasma and platelet VWF multimers. A missense mutation (4115T>G) was found in exon 28 of theVWF gene, which replaced a isoleucine with a serine at position 1372 of pre-pro-VWF (I1372S) at heterozygous level. Recombinant VWF carrying the I1372S mutation and showing a normal VWF multimer organisation was capable of inducing SPA on normal plateletrich plasma (unlike wild-type VWF), as well as a hyper-response to ristocetin in the same platelets (0.6 mg/ml ristocetin vs. 1.2 of wild-type VWF). The new I1372S VWF mutation, characterised by SPA and hyper-responsiveness to ristocetin thus has some of the features of type 2B VWD, but not the lack of large VWF multimers, so we defined this variant as type 2B-likeVWD. Why I1372SVWF is associated with bleeding symptoms, despite normalVWF levels and multimer organisation,remains to be seen.