I have ~100 sets of genes, and each set includes between 2 and 70 genes. I'd like to perform an enrichment analysis on each of these sets to test if they're enriched for OMIM disease labels. However, I'm encountering a problem where the OMIM codes are too "sparse", such that each OMIM code only occurs maximum once in all gene sets. As far as I can tell, this makes the codes unsuitable for enrichment analysis in this case.
I believe that grouping the OMIM codes could solve this, as long as each group-label occurs multiple times in my lists. Grouping OMIM codes seems doable: for example, OMIM codes 601495, 613500, 613502, and 613506 all refer to types of agammaglobulinemia. I could imagine grouping codes based on something like gene ontology labels.
My question: is there a standard way to group OMIM codes?
I see some papers doing something like this, e.g. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4458913/, but I'm new to the field and don't know how "standard" approaches like these are.