Effects of genetics on odor perception: Can a quick smell test effectively screen everyone?

Abstract

SCENTinel, a rapid smell test designed to screen for olfactory disorders, including anosmia (no ability to smell an odor) and parosmia (distorted sense of smell), measures 4 components of olfactory function: detection, intensity, identification, and pleasantness. Each test card contains one of 9 odorant mixtures. Some people born with genetic insensitivities to specific odorants (i.e. specific anosmia) may fail the test if they cannot smell an odorant but otherwise have a normal sense of smell. However, using odorant mixtures has largely been found to prevent this from happening. To better understand whether genetic differences affect SCENTinel test results, we asked genetically informative adult participants (twins or triplets, N = 630; singletons, N = 370) to complete the SCENTinel test. A subset of twins (n = 304) also provided a saliva sample for genotyping. We examined data for differences between the 9 possible SCENTinel odors; effects of age, sex, and race on SCENTinel performance, test-retest variability; and heritability using both structured equation modeling and SNP-based statistical methods. None of these strategies provided evidence for specific anosmia for any of the odors, but ratings of pleasantness were, in part, genetically determined (h2 = 0.40) and were nominally associated with alleles of odorant receptors (e.g. OR2T33 and OR1G1; P < 0.001). These results provide evidence that using odorant mixtures protected against effects of specific anosmia for ratings of intensity but that ratings of pleasantness showed effects of inheritance, possibly informed by olfactory receptor genotypes.

Keywords: genetics; heritability; olfaction; pleasantness; reliability; twins.

Fig. 1.

Accuracy of odor detection and identification (first attempt) across the nine target odors. Odors are listed in order from highest to lowest accuracy, respectively. The number of participants who took each odor is as follows: banana n = 127, bubblegum n = 109, coconut n = 127, coffee n = 96, flower n = 109, lemon n = 67, orange n = 129, strawberry n = 122, woody n = 114.

Fig. 2.

Ratings of odor Intensity and pleasantness for each of the 9 target odors. Odors are in order from highest to lowest mean intensity and pleasantness ratings, respectively. Different letters indicate significant differences (P < 0.05). The number of participants who took each odor is as follows: banana n = 127, bubblegum n = 109, coconut n = 127, coffee n = 96, flower n = 109, lemon n = 67, orange n = 129, strawberry n = 122, woody n = 114.

Fig. 3.

Significant effects of age A) and sex B) on SCENTinel odor intensity ratings. **P < 0.01; ***P < 0.001; ns = not significant. Young = 18–41 years, middle age = 42–63 years, old = 64–88 years.

Fig. 4.

Test–retest reliability for odor intensity and pleasantness.

Fig. 5.

Manhattan plot of the olfactory gene-based association for odor pleasantness. The 2 genes with P-value < 0.001 (dashed line) are labeled.