Low VWF: insights into pathogenesis, diagnosis, and clinical management.

von Willebrand disease (VWD) constitutes the most common inherited human bleeding disorder. Partial quantitative von Willebrand factor (VWF) deficiency is responsible for the majority of VWD cases. International guidelines recommend that patients with mild to moderate reductions in plasma VWF antigen (VWF:Ag) levels (typically in the range of 30-50 IU/dL) should be diagnosed with low VWF. Over the past decade, a series of large cohort studies have provided significant insights into the biological mechanisms involved in type 1 VWD (plasma VWF:Ag levels <30 IU/dL). In striking contrast, however, the pathogenesis underpinning low VWF has remained poorly understood. Consequently, low VWF patients continue to present significant clinical challenges with respect to genetic counseling, diagnosis, and management. For example, there is limited information regarding the relationship between plasma VWF:Ag levels and bleeding phenotype in subjects with low VWF. In addition, it is not clear whether patients with low VWF need treatment. For those patients with low VWF in whom treatment is deemed necessary, the optimal choice of therapy remains unknown. However, a number of recent studies have provided important novel insights into these clinical conundrums and the molecular mechanisms responsible for the reduced levels observed in low VWF patients. These emerging clinical and scientific findings are considered in this review, with particular focus on pathogenesis, diagnosis, and clinical management of low VWF.