Clinical phenotype and pathophysiological mechanisms underlying qualitative low VWF

Area of Science:

• Hematology
• Molecular Biology
• Genetics

Background:

• Some patients with low von Willebrand factor (VWF) and bleeding have normal VWF antigen levels but reduced VWF activity (30-50 IU/dL).
• These cases represent 'qualitative' low VWF, distinct from quantitative VWF deficiency.
• The clinical significance of mild functional VWF defects in these patients is not well-defined.

Purpose of the Study:

• To investigate the clinical implications of mild functional VWF defects in patients with qualitative low VWF (low VWF-QL).
• To determine if low VWF-QL is a distinct clinical entity.
• To explore the underlying mechanisms of low VWF-QL.

Main Methods:

• Combined data from the low VWF in Ireland cohort and the low VWF in Erasmus MC studies.
• Analyzed VWF activity and VWF antigen levels.
• Assessed bleeding phenotypes and investigated VWF sequence variants.

Main Results:

• Low VWF-QL constituted approximately 50% of the combined low VWF cohort.
• Many patients with low VWF-QL (VWF activity 30-50 IU/dL) exhibited significant bleeding despite normal VWF antigen levels.
• Low VWF-QL was identified as a distinct clinic-pathological entity compared to type 2 VWD.
• VWF-QL is primarily caused by VWF biosynthesis abnormalities in endothelial cells, largely independent of sequence variants.

Conclusions:

• Mild functional VWF defects in the 30-50 IU/dL range are clinically significant and associated with bleeding.
• Low VWF-QL is a distinct condition from type 2 VWD.
• Abnormalities in VWF biosynthesis are the likely cause of low VWF-QL.
• These findings have implications for diagnosing and managing patients with mild functional VWF defects.