Learning about genetics has given me a new perspective on so many different subjects. For example, seeing first-hand how much of a difference the right vitamins and minerals make in a person’s mood due to changes in their neurotransmitter balance has made me much more understanding. Cut me off in traffic? Instead of just assuming you are a jerk, I now wonder if you were driving aggressively due to needing a little lithium orotate along with the right type of B12.
One of the things that recently surprised me is that we don’t all smell the same odors. I knew that some people have a loss of the sense of smell when they get older and that inability to smell could be a marker for some diseases, but I was intrigued by the idea that any two people may have as much as a 30% difference in their functional ability to detect different specific odors.[study]
So now I have to once again change my perspective. Over half the population can’t smell a compound in floral fragrance nearly as well as I can. Instead of being irritated at that lady wearing too much floral fragrance, now I recognize that she probably thinks it is lightly pleasant — I’m the one that is different. And now I wonder what it is that I’m not able to smell!
Humans have around 400+ different olfactory receptor proteins that are coded for by our genes. Only a small portion of these receptors have been mapped to specific odors so far. (I’m guessing there isn’t a lot of money in researching olfactory receptors vs. curing diseases…)
There are several different genetic variants of odor receptor genes that aren’t covered by 23andMe. One of them, OR7D4 variant rs5020278, is linked to a persons ability to smell the sex steroid derived odorants, androstenone and androstadienone. Researchers have studied how the ability to detect androstenone plays a role in whether a person is likely to eat pork from uncastrated male pigs. Some people perceive the meat as smelling very unfavorable to eat, known as ‘boar taint’.[study] [study] It turns out that the same odor perception variant can also play a role in sociosexual behaviors in women.[study]
Other studies have linked odor receptor variants to increased BMI. One study found that participants who were less sensitive to smelling oleic acid were more likely to eat more nuts, seeds, and nut spreads (high in oleic acid) as well as having a higher BMI. The study sums up: “fatty acid olfactory sensitivity is clearly linked with fatty acid taste sensitivity albeit acting through separate pathways. Hyposensitivity to fatty acid taste was associated with disinhibited eating behaviour. Furthermore, participants who were hypersensitive to oleic acid taste perception had lower BMI values than those who were hyposensitive.”
So what kind of interesting things can we learn from 23andMe data about what/how we smell odors?
The variant rs6591536 has been linked to the ability to smell β-ionone. Those who carry an G allele are more able to detect β-ionone, which is a floral smell found in roses, jasmine, violets, and more. It is a compound often used by fragrance manufacturers for floral smells. [study]
Check your 23andMe results for rs6591536(v.4 and v.5):
- AA: less able to smell floral (β-ionone)
- AG: more able to smell floral (β-ionone)
- GG: more able to smell floral (β-ionone)
Cilantro is one of those foods that people either seem to love or hate. Turns out that an olfactory receptor gene variant may play a role in how we perceive it. [study]
Check your 23andMe results for rs72921001(v.4 and v.5):
- AA: less likely to think cilantro tastes like soap
- AC: less likely to think cilantro tastes like soap
- CC: more likely to think cilantro tastes like soap
Asparagus pee smell…. was something that I assumed everyone smelled. Turns out that more than half of people in a study of nearly 7000 were unable to smell asparagus pee. A second study looked into whether it was a lack of ability to smell the odor vs. a lack of producing the odor. The study found that 8% of participant’s urine did not have a detectable asparagus odor and also that the ability to smell the asparagus pee smell is much stronger in those who carry the A allele of rs4481887.
Check your 23andMe results for rs4481887 (v.4 and v.5):
- AA: most likely can smell asparagus pee
- AG: likely can smell asparagus pee
- GG: least likely to be able to smell asparagus pee
Being able to smell or not smell certain odors has been linked to food preference and a risk of obesity. For OR7G3, those carrying the C allele variant had almost a whole point higher BMI on average.
Check your 23andMe results for rs10414255 (v.4 and v.5):
- C allele: linked to more hunger, disinhibition in eating, and higher BMI
- TT: lower BMI (on average)
Beyond just smelling the flowers….
While this has been a rather light look at being able to smell different odors, there are more serious issues for people with anosmia (inability to smell) and I encourage you to dig deeper into the topic if you have an inability to smell.
It seems that the research into odorant receptors is just in its infancy with quite a bit of new information coming out in the past couple of years. We actually have these odorant receptors other places than just in our nose, leading to the idea that they play other roles in the body.
“Accumulating molecular evidence indicates that the odorant and taste receptors are widely expressed throughout the body and functional beyond the oronasal cavity – with roles including nutrient sensing, autophagy, muscle regeneration, regulation of gut motility, protective airway reflexes, bronchodilation, and respiratory disease. Given this expanding array of actions, the restricted perception of these GPCRs as mere mediators of smell and taste is outdated.” [study]
HLA typing is also linked to olfactory gene variants. A recent study looked at using smell tests as a way of determining HLA variants.
One last tidbit for your olfactory knowledge base is that some molecules are transformed in the mucus before reaching the odor receptors. CYP1A2 genetic variants (check yours here) were found to play a role in the conversion of acetophenone (cherry, almond chicory smell) to methyl salicylate (wintergreen smell) in the nose.[study] So the whole kit-n-kaboodle gets a little more complicated.
More to read:
- Olfactory Receptors in Non-Chemosensory Organs: The Nervous System in Health and Disease – a review of studies looking at olfactory perception in neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and Creutzfeldt-Jakob disease.
- On the nose: genetic and evolutionary aspects of smell
- Disruptive physiology: olfaction and the microbiome-gut-brain axis.