An overview of our study design is presented in Fig. 1A and is described as follows: This retrospective, observational cohort study includes a total of 92 participants comprised of three study groups, i.e., patients with ACPA+ RA (n = 32), patients with ACPA− RA (n = 30), and healthy controls (n = 30). The gene discussed is PRTN3; the disease is rheumatoid arthritis.