Strange volcano - DEGs with p.adj=0 look weird

Question

[noodlejackson]

Hi everyone,

I am using differential gene expression analysis from Seurat FindMarkers. Some of the DEGs have a p.adj of zero, and therefore form a weird looking ceiling of points in my volcano. I've added a small fudge factor into the ggplot to place them in the range of this plot

y = -log10(adj.P.Val+1e-250) vs y = -log10(adj.P.Val)

Is this ok, or is this a sign of something gone wrong with the stats or presentation? For context I only have a 1000 gene panel! Thanks

EDIT: thought just occurrend, since this is single=cell level, perhaps the p values are inflated due to the huge "sample number". I'll look at pseudobulk to check.

[manaswwm]

What happens when you plot with the p-value instead of the adjusted p-value?