Genetic Assessment of Oesophageal Safety of GLP-1 and GIP Receptor Perturbation: A Drug-Target Mendelian Randomisation Study

Background/Objectives: Glucagon-like peptide-1 (GLP-1) receptor agonists and dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor agonists are used long term for obesity and diabetes, but their oesophageal safety is uncertain: weight loss may reduce Barrett’s oesophagus and adenocarcinoma risk, whereas delayed gastric emptying may worsen reflux. We performed a genetic assessment of target-mediated oesophageal safety. Methods: Two-sample drug-target Mendelian randomisation used cis-expression quantitative trait loci for both receptors (31,684 participants). Outcomes were European genome-wide association studies of gastro-oesophageal reflux disease and the Barrett’s oesophagus/oesophageal adenocarcinoma axis, with a trans-ancestry squamous cell carcinoma comparator. A prespecified gated workflow required positive-control validation, and target specificity required genetic colocalisation (posterior probability of a shared causal variant ≥ 0.70). Candidate metabolic mediators were examined in two-step analyses, and findings were replicated in an independent Finnish population (FinnGen R12). Results: Genetically proxied GLP-1 receptor expression was not associated with reflux disease (odds ratio 0.97, 95% confidence interval 0.85–1.11), arguing against a substantial target-mediated reflux liability; the GIP receptor estimate was not estimable. For the Barrett’s oesophagus/adenocarcinoma endpoint, estimates were near the null for both receptors (GLP-1R 0.96, 0.47–1.96; GIPR 1.00, 0.42–2.37); colocalisation was uninformative because the outcome loci carried no detectable association signal, and wide intervals did not exclude moderate effects. The null reflux findings were reproduced in FinnGen. Adiposity showed the most consistent pathway association, whereas glycaemic traits did not, including when HbA1c was instrumented from a population-based genome-wide association study providing an order of magnitude more variants. Conclusions: GLP-1 receptor perturbation was not associated with reflux disease, providing cautious genetic reassurance. For the Barrett’s oesophagus/adenocarcinoma axis, no target-specific association was demonstrated, but colocalisation was uninformative because the outcome loci carried no detectable signal, and imprecision precludes firm safety conclusions; larger adenocarcinoma-specific studies are warranted.