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Chemosensory Mendelian Randomization

Summary

Chemosensory Mendelian Randomization is an epidemiological method that addresses key limitations in nutritional epidemiology by using genetic variants in taste and olfactory receptors as instrumental variables (IVs). By focusing on variants that alter chemosensory perception (such as taste and smell) and shape lifelong food preferences before the onset of chronic diseases, this framework reduces susceptibility to horizontal pleiotropy and reverse causation. It provides a biologically grounded alternative to traditional dietary Mendelian Randomization studies, which typically select genetic instruments based solely on statistical significance in genome-wide association studies (GWAS) of self-reported food intake.

Biological Rationale and Limitations of Standard Dietary MR

Traditional dietary MR relies on genetic variants identified in GWAS of self-reported food intake. However: - Reverse Causation: Self-reported dietary intake in adults is often modified in response to subclinical or diagnosed health conditions (e.g., individuals with high body mass index reducing sugar intake due to FTO variants, or those at risk of cardiovascular disease reducing fried food consumption due to APOE variants). - Horizontal Pleiotropy: Many genetic variants associated with food intake affect downstream metabolic pathways directly rather than acting purely through dietary behavior, violating the exclusion restriction assumption of MR.

Chemosensory MR overcomes these issues by targeting G-protein coupled receptors (GPCRs) in the oral and nasal cavities: - Taste Receptors: The TAS1R gene family (sweet, umami, and savory tastes) and TAS2R gene family (bitter tastes). - Olfactory Receptors: The OR gene family (mediating detection of volatile odorants).

Because these receptors determine primary sensory perception and food liking from early childhood, the associated genetic variants reflect lifelong exposure profiles and are less influenced by disease-driven behavioral changes.

Key Applications and Findings

Using this approach, Hwang et al. identified 268 nonsynonymous variants associated with 96 food-liking traits in the UK Biobank, filtering them down to 24 candidate instruments. A primary highlight was: - Onion Liking: Proxied by the variant rs6587467 in the olfactory receptor gene OR2T6, which exhibits expression localized to the olfactory epithelium. - Cardiometabolic Effects: Mendelian randomization using this high-confidence instrument showed that genetically proxied onion liking is causally linked to lower systolic and diastolic blood pressure and a reduced risk of type 2 diabetes, suggesting a potential role for bioactive organosulfur compounds and flavonoids (like quercetin) found in onions.

  • Evans Lab — statistical-genetics and MR methodology for dietary exposures.
  • Joseph Lab — sensory science and metabolism research.
  • Reed Lab — genetics of taste and smell perception.

Citations

  • Hwang, L. D., Lin, C., Evans, D. M., Martin, N. G., Reed, R. D., & Joseph, P. V. (2026). A biologically informed framework for instrument selection in dietary Mendelian randomization using chemosensory genetics. BMC Medicine, 24:359. DOI: 10.1186/s12916-026-04966-x. Source paper: s12916-026-04966-x.pdf
  • Sanderson, E. et al. (2026). Challenges and future directions for Mendelian randomization. Nature Genetics, 58(5), 984–994. DOI: 10.1038/s41588-026-02546-6. Source paper: s41588-026-02546-6.pdf