In vivo functional evaluation demonstrates variable severity of defects in VUS. Human F5 variants were engineered into the orthologous positions in the zebrafish f5 cDNA under the control the of the ubiquitin promoter. Expression vectors were injected into 1-cell stage embryos from f5 heterozygous incrosses. Laser-mediated endothelial injury was performed at 3 dpf and time to occlusion recorded, followed by genotyping. Although Y1702C and G97D demonstrated residual occlusion, they were unable to effectively rescue (P < .0001, P = .002, respectively, by the Mann-Whitney U test). Conversely, S83R, R2074C, and R2187C did not show statistically significant differences from wild-type rescue (not significant by the Mann-Whitney U test). Horizontal bars represent the median time to occlusion. Numbering reflects the human amino acid positions.