Association between diabetes mellitus and giant cell arteritis: a bidirectional 2-sample mendelian randomization study

Objective Recent studies have indicated a potential association between giant cell arteritis (GCA) and diabetes mellitus, encompassing both type 1 diabetes (T1D) and type 2 diabetes (T2D). However, the exact nature of this relationship requires further investigation to be fully elucidated. Methods Genetic links between T1D/T2D and GCA were explored using data from genome-wide association studies available to the public, focusing on populations of European ancestry. We applied a bidirectional mendelian randomization (MR) approach to assess the potential association between these diseases. Confirmatory analyses, including additional datasets and a comprehensive meta-analysis, were utilized. The inverse-variance-weighted (IVW) method was applied to pinpoint heterogeneity and pleiotropy, while subsequent sensitivity analyses aimed to trace the origins of any heterogeneity. Results Initial analysis demonstrated a correlation between T1D and an elevated likelihood of developing GCA (IVW odds ratio = 1.33, with a 95% confidence interval of 1.22-1.46, and a P-value of 9.42E-10). The causal association was verified through four validation datasets and meta-analysis (all P-value < 0.001). However, the reverse MR analysis was unable to detect any genetic basis for the increased risk of T1D due to GCA. Furthermore, we could not establish any causal links between T2D and GCA. Conclusion T1D patients may have a higher risk of developing GCA, whereas an inverse causal relationship was not evident. Furthermore, no causal relationship was detected between T2D and GCA. These insights shed light on the possible pathological mechanisms underlying GCA and may influence the future clinical handling of both T1D and GCA.