I have RNA Seq for 2 groups of patients, Group1 with 4 patients and Group 2 with 5 patients. I want to find differences between the two groups (Grouo1 vs Group2) as well as whether a gene is up- or down regulated in one group vs the other. A first thought would be to use the Mann-Whitney test.
In order to limit the results I would like to do other tests and focus on the common results (the intersection). What other alternatives would I have?