A Missense Mutation in Exon 28 (C4120T) of the Von Willebrand Factor Gene is the Cause for Von Willebrand Disease in a Large Amish Pedigree

Abstract number: P1472

Di Paola¹ J, Murray¹ J, Lentz² S, Montgomery³ R, Sayago¹ C, Wang⁴ K, Burns⁴ T, Shapiro⁵ A

¹¹University of Iowa, Pediatric, Iowa City, IA, USA ¹¹University of Iowa, Pediatric, Iowa City, IA, USA ²²University of Iowa, Internal Medicine, Iowa City, USA ³³Blood Research Institute, Milwaukee, WI, USA ⁴⁴University of Iowa, College of Public Health, Iowa City, IA, USA ⁵⁵Indiana Hemophilia and Thrombosis Center, Indianapolis, IN, USA

We have identified and characterized a single 758-individual Amish pedigree diagnosed with von Willebrand disease (VWD). Blood samples were collected from 212 subjects. 52 individuals were affected with VWD as defined by VWF antigen (VWF : Ag) or von Willebrand Ristocetin Cofactor (VWF : RCo) <45 U/dL. 70 individuals exhibited a bleeding phenotype as defined by a score >=3 in a bleeding questionnaire. The correlation of these two phenotypes was not absolute. A discrepancy between VWF : Ag and VWF : RCo levels suggested type 2 VWD in the affected individuals. In a subset of affected individuals, VWF multimer analysis showed a normal pattern. The overall means for VWF : Ag, VWF : RCo and Factor VIII : C were 27, 22 and 52 U/dL for individuals with VWD and 106, 116 and 123 U/dL for unaffected individuals (P < 0.05). Linkage analyses showed minimal evidence for linkage between age- and gender-adjusted VWF levels and the ABO gene, likely due to a very high frequency of genotype O₁O₁ in the pedigree. Informative polymorphic markers in intron 40 of the VWF gene in a subset of the pedigree (72 individuals) showed linkage to VWD (VWF : Ag <45) with a LOD score of 2.23 (P= 0.00068). Sequencing of exon 28 of the VWF gene demonstrated a missense mutation at position 4120, represented by a single base substitution (C > T) that predicts an arginine to cysteine change at position 1374 in the A1 domain of the mature VWF molecule. This mutation has been described previously in an individual with type 2 VWD. All 52 individuals with VWF levels < 45 U/dL exhibited the C4120T substitution. The C4120T mutation was not found in a control Caucasian population (n= 247). This large pedigree represents a unique resource for linkage analysis and subsequent discovery of modifying genes for VWF levels and bleeding.