Hi,

I have 4 groups (A, B, C, and D) with 1 sample each and I want to check for differential gene expression analysis as follows: A vs B A vs C A vs D A vs (B + C + D) A vs (B + C) (A + D) vs (B + C)

How to perform DESeq 2 on 1 vs 1, as the degree of freedom will be 0 in this case?

It's not possible / supported. This has been asked many times before.