PRTN3 and rheumatoid arthritis: Moreover, we could not replicate the association of metabolic biomarkers with incident RA found in previous studies,25 26 especially the lack of biomarkers related to sex hormones, which influence immune cell development and have immunomodulatory effects.48 49 Furthermore, with regard to potential genetic and metabolic pathway differences that might exist among different ACPA (anti-cyclic citrullinated peptide antibodies)-RA serological types,50 51 we could not investigate this heterogeneity due to the unavailability of ACPA data in the UKB.