Anti‐Ro52/TRIM21 autoantibodies predict Sjögren's syndrome in patients with primary biliary cholangitis

Abstract Background and aims Sjögren's syndrome is a common comorbidity in patients with primary biliary cholangitis (PBC). Anti‐Ro52 autoantibodies against the protein TRIM21 are often seen in Sjögren's syndrome. TRIM21 consists of four domains (PRY/SPRY, Coiled‐Coil, B‐box, and RING domain), each with a specific function. We hypothesized that patients with PBC and concomitant autoantibodies against TRIM21 had a higher risk of developing Sjögren's syndrome. Methods Using ELISA, we analyzed plasma from 236 Danish patients with PBC. Binomial regression assessed the risk rates between demographics, serologic variables, PBC‐40 results, and autoantibody positivity. Results Forty patients (16.9%) tested positive for anti‐Ro52 autoantibodies, with 23 (9.7%) samples positive against Coiled‐Coil, 12 against PRY/SPRY (5.1%), and 10 against RING (4.2%). Increased IgG plasma levels, reports of dry mouth , and a diagnosis of Sjögren's syndrome increased the risk of both anti‐Ro52 and all domain autoantibodies. In the anti‐Ro52 positive subgroup, no less than 14 undiagnosed patients met the criteria for Sjögren's syndrome. Conclusions We observed a 16.9% positivity of anti‐Ro52 autoantibodies and an association between having these autoantibodies and elevated IgG, the symptom dry mouth, and having Sjögren's syndrome. Furthermore, we found a sizable undiagnosed group of Sjögren's patients in the anti‐Ro52 positive subgroup. Our results suggest that Sjögren's patients are underdiagnosed in patients with PBC. We propose that patients with PBC be tested for anti‐Ro52 autoantibodies and, if positive, referred for rheumatological examination.