In general, dysregulation of Claudin 1 expression contributes to numerous autoimmune diseases including rheumatoid arthritis, type 1 diabetes, multiple sclerosis, or inflammatory bowel disease (Sapone et al., 2006; Weber et al., 2008; Mandel et al., 2012; Tajik et al., 2020). This evidence concerns the gene CLDN1 and rheumatoid arthritis.