Insulin Resistance-Related Traits and Diabetic Maculopathy: Causal Insights from Mendelian Randomization

Background/Objectives: To investigate the causal relationships linking body mass index (BMI) and circulating insulin-like growth factor 1 (IGF-1) levels with diabetic maculopathy risk using two-sample Mendelian randomization (MR). Methods: A two-sample MR framework was applied, utilizing genetic instruments for BMI and IGF-1 derived from the UK Biobank. Summary-level diabetic maculopathy data were obtained from the FinnGen consortium. Genome-wide significant single-nucleotide polymorphisms (SNPs, p < 5.0 × 10^-8) independently associated with each exposure were employed as instrumental variables. Primary causal estimates were obtained using the inverse-variance weighted (IVW) method. Sensitivity analyses, including MR-Egger regression, weighted median methods, and the MR-Pleiotropy RESidual Sum and Outlier (MR-PRESSO), were conducted to evaluate robustness and potential pleiotropy. Results: Genetically predicted BMI was positively associated with diabetic maculopathy risk in both the IVW analysis (odds ratio [OR] = 1.16 (95% confidence interval [CI]: 1.04-1.30), p = 0.008) and MR-PRESSO (OR = 1.16 (95% CI: 1.04-1.28), p = 0.006). MR-PRESSO exhibited a significant relationship between higher IGF-1 levels and increased diabetic maculopathy risk (OR = 1.09 (95% CI: 1.01-1.18), p = 0.025), whereas the IVW method indicated only a suggestive association (OR = 1.08 (95% CI: 0.99-1.18), p = 0.087). Conclusions: The genetic evidence supports a causal role of insulin resistance-related traits in diabetic maculopathy development, with higher BMI and IGF-1 levels increasing diabetic maculopathy risk. These results underscore the potential contributory role of IGF-1 in disease pathogenesis and suggest that insulin resistance-related traits may represent preventive therapeutic targets.