Genetic variation in UGT2A1 is not associated with ratings of odor intensity or pleasantness in human twins

Poster presentation

Liang-Dar Hwang ^{1, 2}, Mackenzie Hannum ³, Paule Joseph ^{4, 5}, Alissa Nolden ⁶, Katherine Bell ³, Cailu Lin ³, Scott Gordon ², Nicholas Martin ², Margaret Wright ⁷, Sarah Marks ³, Akane Kikuchi ³, Aurora Toskala ³, Danielle Reed ³

¹ Institute for Molecular Bioscience, The University of Queensland, St Lucia, Queensland, Australia, ² QIMR Berghofer Medical Research Institute, Herston, Queensland, Australia, ³ Monell Chemical Senses Center, Philadelphia, PA, USA, ⁴ National Institute of Alcohol Abuse and Alcoholism, NIH, Bethesda, MD, USA, ⁵ National Institute of Nursing, NIH, Bethesda, MD, USA, ⁶ University of Massachusetts, MA, USA, ⁷ Queensland Brain Institute, The University of Queensland, St Lucia, Queensland, Australia

We followed up on a recent report and an accompanying blog post that a particular genotype is associated with more significant smell loss in people with COVID-19 and a worse overall sense of smell in people who are not sick. This genotype is within two genes, the code for enzymes that metabolize odorants like eugenol (but not other odorants like amyl acetate; UGT2A1/A2, UDP-glucuronosyltransferases). A convenience sample of human twins (studied before COVID-19 pandemic) rated six odorants (using scratch and sniff methods) for intensity and pleasantness. We grouped twins by genotype and found no differences in ratings of odorant intensity or pleasantness among those with high vs. low-risk alleles (rs7688383; N=879; all p-values >0.05). Participants with the high-risk allele rated eugenol intensity (p=0.46) and pleasantness (p=0.83) similarly to people with the low-risk allele. In a small, separate study of 27 twins who had COVID-19, we found that the risk allele did not predict smell loss (p=0.29). We need to test more people with more sensitive psychophysical methods to understand whether this genetic variation affects the sense of smell in people without COVID-19, and this data collection is ongoing.