Von Willebrand disease - phenotype versus genotype: deficiency versus disease

Area of Science:

• Hematology
• Genetics
• Molecular Biology

Background:

• Von Willebrand disease (VWD) is categorized into three main subtypes: type 1 (partial quantitative deficiency), type 2 (qualitative defects including 2A, 2B, 2M, 2N), and type 3 (near-complete deficiency of von Willebrand factor (VWF)).
• Subtypes of type 2 VWD involve distinct defects: 2A (low-molecular-weight VWF), 2B (increased platelet binding), 2M (impaired adhesion despite normal VWF size), and 2N (reduced factor VIII binding).
• Genetic underpinnings for VWD subtypes are increasingly understood, with type 3 linked to null mutations and type 2N to specific missense mutations affecting factor VIII binding.

Purpose of the Study:

• To explore the association between specific genetic variants of von Willebrand factor (VWF) and the resulting disease phenotype in Von Willebrand disease (VWD).
• To characterize the molecular pathogenesis of type 1 VWD, highlighting the diverse genetic changes involved.
• To investigate the complexity of genetic factors contributing to type 1 VWD, including potential involvement of genes beyond VWF.

Main Methods:

• Classification of VWD into subtypes based on quantitative and qualitative von Willebrand factor (VWF) defects.
• Analysis of genetic variants, including missense, splice site, and transcriptional mutations, in patients with Von Willebrand disease (VWD).
• Examination of VWF gene sequences and assessment for multiple variant sequences or absence of detectable changes in affected individuals.

Main Results:

• Type 3 VWD is associated with mutations leading to a null phenotype, while type 2N VWD results from recessive missense mutations impairing factor VIII binding.
• Molecular characterization of type 1 VWD reveals a broad spectrum of genetic alterations, with patients often heterozygous for various mutations.
• In some type 1 VWD cases, multiple variant VWF sequences were identified, and in a significant number, no VWF gene changes were detected, suggesting other genetic factors may be involved.

Conclusions:

• The genetic basis for Von Willebrand disease (VWD) subtypes is diverse, with specific mutations correlating with distinct phenotypes.
• The molecular pathogenesis of type 1 VWD is complex, involving a wide range of genetic changes at the VWF locus.
• The genetic architecture of type 1 VWD likely extends beyond the VWF gene itself, implicating mutations in other genes.