Genetic analysis of 31 Swedish type 1 von Willebrand disease families reveals incomplete linkage to the von Willebrand factor gene and a high frequency of a certain disease haplotype

Background: The most common type of von Willebrand disease (VWD), type 1, has in only a few cases been explained by an identified causative mutation in the von Willebrand factor (VWF) gene. The ABO blood group and other modifier loci outside the VWF gene may contribute to the development of type 1 VWD. Objectives and methods: Our aim was to determine whether there was genetic linkage to the VWF gene in 31 Swedish type 1 VWD families. Stringent diagnostic criteria in accordance with ISTH guidelines were used. Genetic linkage was investigated by using two highly informative dinucleotide microsatellite markers, which we have recently identified, located in introns six and 15 of the VWF gene. We also investigated the existence of common disease haplotypes and the relation between type 1 VWD and ABO blood group. Results: We found genetic linkage to the VWF gene in 27 (87%) of the families. However, in four (13%) of the families, there was clearly no genetic linkage. We found the 4751A > G (Tyr1584Cys) sequence variation in exon 28, which is a common mutation in the Canadian VWD population (14.3%), in only one of the 31 families (3.2%). A possible common mutation was identified in six of the 27 (22%) families with genetic linkage. Blood group O was over-represented among type 1 VWD patients. Conclusion: We conclude that there is linkage between the VWF gene and hereditary type 1 VWD in a majority of families.