Project 4 will utilize the two large type 1 von Willebrand disease populations from Canada and Europe to broaden the analysis of the US Study in Project 1 and provide a common database for this and future studies. The availability of extensive genetic sequence information and additional plasma and DMA samples from 348 type 1 VWD families plus 1366 normal controls enrolled in the European Union and Canadian multicenter projects will provide a unique resource for the objectives comprising Project 4. Aim 1 will test the hypothesis that sequence variation in non-coding areas of the VWF locus plays a role in regulating plasma VWF levels. Type 1 VWD families in which low plasma VWF and bleeding phenotypes are linked to the VWF gene locus but in which sequence analysis has failed to demonstrate candidate mutations in the VWF coding regions and splice junctions will be investigated. Aim 2 will investigate the influence of haplotype interactions within the VWF locus on VWF expression. Haplotype blocks will be generated from type 1 VWD patients and from unaffected family members, to assess their association with VWF plasma levels. This analysis will be complemented by in vitro protein expression and mouse studies in which different VWF cDNA haplotypes will be evaluated for their effect on VWF expression and survival. These studies will integrate with those described in Project 2. Aim 3 will test the hypothesis that sequence variation affecting VWF mRNA splicing plays a role in the pathogenesis of type 1 VWD. These studies will assess the extent of physiologic alternative splicing at the VWF locus and will employ mini-genomic constructs and platelet VWF mRNA analysis to evaluate the effect of splice junction and exon splice enhancer mutations on the pattern of VWF transcript processing. The final objective, Aim 4, will focus on those families in which the type 1 VWD phenotype has been demonstrated not to be linked to the VWF locus. These studies will evaluate loci identified in Project 3 by Drs DiPaola and Ginsburg as well as previously proposed candidate genes.