Molecular findings:

Severe bleeding phenotype in homozygotes, alleviated bleeding phenotype in heterozygotes.

Difficult to classify based on the phenotype and plasma levels.

p.M771V variant shows elevated proVWF to mature VWF ratio, reduced levels of cleaved VWFpp.

p.M771V has potential to negatively influence VWFpp cleavage to contribute to decreased VWF processing in endothelial cells.

Other variants near p.M771 locus reported to disrupt the cleavage by furin. (Variants are at R763 and R760 respectively).

Other researchers have come across the p.M771 variant and reported it as well.

functional studies performed in cord blood derived ECFCs through adenine base editing and overexpressed in HEK293 cells.

Utilized Immunocytochemistry staining and confocal analysis

ELISA to test for secreted VWF in ECFCs

Multimer assay and densitometry graphs to view VWF multimer patterns

Western blotting to view proteolytic processing of VWF and VWFpp

Genomic sequencing to verify mutations.

Authors here used SpCas9-mediated base editing to mimic patient variant if primary ECFCs are not available or are difficult to culture to assist in improved characterization in a true endothelial background.

WHO. (n.d.) Coronavirus disease (COVID-19) technical guidance: Laboratory testing for 2019-nCoV in humans. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/technical-guidance/laboratory-guidance