Using Summary-data-based Mendelian Randomization (SMR) anchored to the eQTL variant rs9283907 as an instrumental variable for GLP1R expression, this analysis found no statistically significant causal effects on total bone mineral density (β: −0.03, p=0.702), osteoporosis risk (β: 0.00, p=0.416), fracture incidence (β: 0.09, p=0.343), appendicular lean mass (β: −0.01, p=0.676), grip strength (β: −0.02, p=0.425), or walking pace (β: 0.00, p=0.216). Positive controls — T2D and BMI reduction — performed as expected, validating the analytical framework.
The clinical urgency here is real. As GLP-1 receptor agonists like semaglutide become blockbuster weight-loss drugs, a persistent concern is whether rapid weight reduction accelerates muscle wasting or bone resorption — risks documented in caloric-restriction and bariatric surgery contexts. This genetic analysis offers a reassuring but partial answer: lifelong variation in GLP1R expression does not inherently compromise musculoskeletal architecture, suggesting the receptor pathway itself is not the culprit.
The critical limitation is the method's own ceiling. Mendelian randomization captures constitutional receptor expression, not the pharmacodynamic surge produced by supraphysiological drug dosing, caloric deficit, or rapid fat loss — all clinically relevant to semaglutide users. Real-world attenuation of lean mass observed in some trials likely reflects weight loss mechanics rather than direct GLP1R biology. This is confirmatory but incomplete evidence; long-term RCTs with DEXA-measured body composition remain indispensable before broad musculoskeletal safety can be declared.
