KL and rheumatoid arthritis: When RA was considered as the exposure to explore bidirectional associations, no significant genetically predicted associations were observed (Tables S3 and S4, Supplemental Digital Content, https://links.lww.com/MD/P606 and Figure S1, Supplemental Digital Content, https://links.lww.com/MD/P604, indicating the absence of causal effects of RA on Klotho (IVW: β = −0.030, 95% CI = −0.073–0.012, P = .161).