Genetically predicted frailty index and risk of chronic kidney disease

Previous findings have reported the association between frailty and chronic kidney disease. However, the causality remains ambiguous. This study aimed to determine whether frailty index is causally associated with chronic kidney disease. We obtained the frailty genome-wide association study (GWAS) data and chronic kidney disease GWAS data from the FinnGen R5 (total n = 216,743; case = 3902, control = 212,841) as the exposure and outcome, respectively. A two-sample Mendelian randomization (MR) analysis was primarily conducted using the inverse-variance weighted (IVW), weighted median and MR-Egger regression analyses. Multivariable MR analysis (MVMR) was conducted for additional adjustment. In the two-sample Mendelian randomization analyses, a total of 14 single nucleotide polymorphisms (SNPs) were recognized as effective instrumental variables. The IVW method showed evidence to support a causal association between frailty index and chronic kidney disease (beta = 1.270; 95% CI 0.608 to 1.931; P < 0.001). MR-Egger revealed a causal association between frailty index and chronic kidney disease (beta = 3.612; 95% CI 0.805 to 6.419; P = 0.027). MR-Egger regression revealed that directional pleiotropy was unlikely to be biasing the result (intercept =  - 0.053; P = 0.119). The weighted median approach and weighted mode method also demonstrated a causal association between frailty index and chronic kidney disease (beta = 1.148; 95% CI 0.278 to 2.019; P = 0.011; beta = 2.194; 95% CI 0.598 to 3.790; P = 0.018). Cochran's Q test and the funnel plot indicated no directional pleiotropy. MVMR analysis revealed that the causal association between frailty index and chronic kidney disease remained after adjusting for potential confounders, body-mass index, inflammatory bowel disease, waist-hip ratio, and C-reactive protein. Our study provides evidence of causal association between frailty and chronic kidney disease from genetic perspectives.