An apparently silent nucleotide substitution (c.7056C>T) in the von Willebrand factor gene is responsible for type 1 von Willebrand disease

Abstract

BackgroundNucleotide variations not changing protein sequences are considered silent mutations; accumulating data suggest that they can, however, be important in human diseases. Design and MethodsWe report an altered splicing process induced by a silent substitution (c.7056C>T) in the von Willebrand factor gene in a case of type 1 von Willebrand disease originally classified as lacking von Willebrand factor mutations. ResultsThe c.7056C>T synonymous substitution introduces a new donor splice site within exon 41, leading to messenger RNA lacking nucleotides 7055-7081 (c.7055_7081del). The encoded von Willebrand factor protein is predicted to lack amino acids 2352-2360 in the B2 domain. The patient's von Willebrand disease phenotype was characterized by reduced plasma and platelet von Willebrand factor, which was normal in function and multimer structure. In vitro expression studies demonstrated that co-transfection of equimolar c.7055_7081del and wild-type von Willebrand factor (mimicking the patient's heterozygous state) induced a 50% lower von Willebrand factor secretion than the wild type, while almost no von Willebrand factor secretion was seen with the mutated von Willebrand factor alone. The secreted von Willebrand factor was structurally and functionally normal, suggesting that the c.7056C>T substitution behaves like a loss-of-function allele. ConclusionsThis is the first report of a synonymous von Willebrand factor substitution being responsible for von Willebrand disease. Our findings suggest the need to reconsider the role of von Willebrand factor polymorphisms in von Willebrand disease.

Type 2N von Willebrand disease: Characterization and diagnostic difficulties

“…17,18 Heterozygotes for type 2N VWF are considered carriers of the defect, like haemophilia A carriers, and they are mostly asymptomatic.…”

Variable content of von Willebrand factor mutant monomer drives the phenotypic variability in a family with von Willebrand disease

“…It is now recognized from large studies of families with VWD that, in addition to characterized VWD mutations, several polymorphisms modify VWF levels and may modify VWF activity. 13,[26][27][28] We therefore measured the levels of mutant and normal VWF mRNA in affected and unaffected members of the pedigree to investigate the potential contribution of a hypomorphic normal allele to the observed phenotypic variability. The levels of the normal mRNA were similar among the affected individuals carrying the M1304R variant, ranging from 73% to 78% of total VWF mRNA, ruling out a contribution of a hypomorphic allele (supplemental Figure 2).…”

The molecular basis of von Willebrand disease: the under investigated, the unexpected and the overlooked

“…The mutation results in p.Gly2352_Cys2360del in the B2 domain. 11 This study highlights that mutations could be overlooked during standard VWF molecular analysis because they are perceived as being not disease-causative. Notably, the c.7056C>T mutation was previously observed in the Canadian type 1 VWD study, but was reported as a polymorphism.…”

“…In this issue of the journal, Daidone et al 11 highlight a mutation previously overlooked in VWF molecular analysis. The authors analyzed all 52 exons, flanking intronic sequence and the 5' and 3' untranslated regions of VWF in a family diagnosed with mild-moderate type 1 VWD.…”