I have a RNA-Seq data set (normalized using the DESeq2 library normalization method) consisting 4200 genes and of samples from 22 different species. For each species I have four samples (one for the liver, one for the brain, the kidney and the lung). But I don't want to consider organ dependent variations. What I am looking for are for genes whose expression changes through species, but not through organs. So my question is, can I consider the categorical variable 'Organ type' as a batch effect in order to eliminate its influence with the ComBat function? If it is not advisable to do that, do you have any recommendation?
*Note: Because I only have 122 samples, I don't think it is advisable to split the data set by organ type.
Thanks a lot