To date, no dominant mutation has been identified in a significant proportion of patients with type 1 von Willebrand disease (VWD). In this study, we examined 70 families as part of the Canadian Type 1 VWD Study. The entire VWF gene was sequenced for 1 index case, revealing 2 sequence variations: intron 30 (5312؊19A>C) and exon 28 at Tyr1584Cys (4751A>G). The Tyr1584Cys variation was identified in 14.3% (10 of 70) of the families and was in phase with the 5312؊19A>C variation in 7 (10.0%) families. Both variants were observed in 2 of 10 UK families with type 1 VWD, but neither variant was found in 200 and 100 healthy, unrelated persons, respectively. Mean von Willebrand factor antigen (VWF:Ag), VWF ristocetin cofactor (VWF:RCo), and factor VIII coagulant activity (FVIII:C) for the index cases in these families are 0.4 U/mL, 0.36 U/mL, and 0.54 U/mL, respectively, and VWF multimer patterns show no qualitative abnormalities. Aberrant VWF splicing was not observed in these patients, and both alleles of the VWF gene are expressed as RNA. Molecular dynamic simulation was performed on a homology model of the VWF-A2 domain containing the Tyr1584Cys mutation. This showed that no significant structural changes occur as a result of the substitution but that a new solvent-exposed reactive thiol group is apparent. Expression studies revealed that the Tyr1584Cys mutation results in increased intracellular retention of the VWF protein. We demonstrate that all the families with the Tyr1584Cys mutation share a common, evolved VWF haplotype, suggesting that this mutation is ancient. This is the first report of a mutation that segregates in a significant proportion of patients with type 1 VWD. (Blood. 2003;102:549-557)
Summary. Background: Type 1 VWD is associated with mutational heterogeneity in the VWF gene. The R924Q substitution was the second most frequent sequence variation in the Canadian type 1 VWD study and this variant was also documented in other type 1 VWD studies. In this study, R924Q was detected in a compound heterozygote possessing both type 2N and 924Q substitutions whose VWF:FVIIIB and FVIII levels were disproportionately low for the heterozygous type 2N state. Aim: To determine the role of R924Q variation in the pathogenesis of type 1 VWD. Methods: The frequency of the R924Q variant in the normal and type 1 VWD populations was ascertained, along with the associated polymorphic VWF haplotype. The effect of the R924Q substitution on the biosynthesis and intracellular trafficking of VWF was explored by in vitro expression studies in COS-7 and AtT-20 cells. Immunofluorescent staining of VWF was performed in transfected AtT-20 cells and BOECs from the patient. RNA analysis was performed to investigate an RNA processing defect in the patient. Results and Conclusions: In vitro expression studies demonstrated that the R924Q variation does not affect biosynthesis, intracellular trafficking and storage significantly. Storage of VWF in the patientÕs endothelial cells was abnormal. Analysis of the patientÕs VWF mRNA revealed a novel truncated transcript resulting from the activation of a cryptic splice site in exon 28. The presence of a common VWF haplotype in heterozygotes for 924Q with low VWF levels suggests a founder origin for this variant allele that may mark this splicing defect.
Summary. Background: Plasma von Willebrand factor (VWF) is mainly derived from endothelial cells, cells that express a large repertoire of genes that are transcriptionally regulated by fluid shear stress. Endothelial VWF expression is not uniform throughout the vasculature, and levels are increased at regions associated with disturbed blood flow and steep gradients of shear stress. It is, however, unknown whether shear stress influences the regulation of VWF gene expression. Objectives: Our objective was to evaluate the effect of shear stress on endogenous endothelial VWF mRNA expression and VWF promoter () 2722 to ) 1224) activity and to determine whether genetic elements modulate this flow-induced expression. Methods: A parallel plate flow chamber was used to expose endothelial cells to a shear level of 15 dynes cm )2 for 24 or 6 h.VWF mRNA expression was analyzed. Various VWF promoter constructs that each contain either SNP haplotypes 1 or 2 and either a 17-GT or a 23-GT repeat element were transfected into endothelial cells, and flow-induced promoter activation was assessed. Results: When endothelial cells were exposed to shear stress, endogenous VWF mRNA expression increased 1.84-fold and average VWF promoter activity was enhanced 3.4-fold. Single nucleotide polymorphisms at ) 2708 and ) 2525, and the shear stress-response element at ) 1585, are not responsible for the shear stress-induced increase. Rather a GT repeat element at ) 2124 mediates the increase in activity, and the length of this polymorphic repeat element influences the magnitude of induction. Conclusions: Shear stress enhances VWF promoter activity and a polymorphic GT repeat element mediates the stress-induced transactivation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.