HLA-DRB1 and rheumatoid arthritis: Specifically, taxon-level analysis identified an expansion of rare taxa, Actinobacteria, with a decrease in abundant taxa in RA patients compared to controls, and found three genera, Collinsella, Eggerthella and Faecalibacterium, to be associated with RA.[24] Additionally, RA patients with the HLA-DRB1 allele epitope, and especially those who become anti citrullinated protein antibody (ACPA) positive, are at-risk of RA.