Key takeaways:
~ Odor receptors are proteins located on the cell membrane of specific types of cells that can bind to odorant molecules.
~ Genetic variants in the odor receptor genes mean that individuals can detect odors differently or at different levels.
~ This article looks into the genetic variants in the odor receptor genes and how they influence one’s response to their environment.
Odor receptors: More than how things smell
Humans have around 400+ different olfactory receptor proteins coded for by our genes. So far, only a small portion of these receptors have been mapped to specific odors.
Scenario: You are walking through the grocery store aisle, and it seems as if someone has left a trail of perfume. Thick perfume, heavy on the floral scents… You quickly look around for the offender to your olfactory senses. Before you decide to make a comment to the offender, think about this — any two people may have as much as a 30% difference in their functional ability to detect different specific odors due to genetic variants. [ref]
How do odor receptors work?
The olfactory receptor proteins are receptors on the surface of certain cells that can bind with specific molecules. When the odorant molecule binds to the receptor, it triggers actions within the cell, causing signals to be sent to the olfactory center in the brain.
These receptor proteins, located in the airway passages such as the nose, let your brain know that you are smelling something. Most odor receptors can bind to multiple different molecules, and how well the molecules bind gives rise to the strength with which you perceive an odor.
As you can imagine, detecting certain odors is vital for determining whether food is edible, whether something is toxic or dangerous, and for sexual preference.
OR7D4 variant:
Take, for example, an OR7D4 variant, rs5020278, which is linked to a person’s ability to smell the sex steroid-derived odorants, androstenone, and androstadienone.
Researchers have studied how the ability to detect androsterone 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’.[ref][ref] It turns out that the same odor perception variant can also play a role in sociosexual behaviors in women.[ref]
Other studies have linked odor receptor variants to increased BMI. One study found that participants who were less sensitive to smelling oleic acid, a type of fat, were more likely to eat more nuts, seeds, and nut spreads (high in oleic acid) as well as have a higher BMI. Essentially, a decreased ability to taste that specific fat led to eating significantly more fatty foods. Conversely, the ability to smell the fat was linked to a lower BMI.[ref]
Beyond just smelling the flowers…
Recent research shows odor receptors aren’t just limited to the nose. They work as chemical sensors in other parts of the body. For example, sperm cells have at least three different odor receptors on their surface, which may help in chemically detecting the egg cell.[ref]
“Accumulating molecular evidence indicates that the odorant and taste receptors are widely expressed throughout the body and function 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.”[ref]
Odor receptors may also play a role in Parkinson’s and Alzheimer’s diseases. Additionally, the sciatic nerve has odor receptors, which may play a role in pain.[ref][ref]
A recent (June 2020) study found specific olfactory receptor variants have links to eating habits, such as the number of fruits and vegetables eaten or the likely cups of tea people drink.[ref]
HLA typing is also linked to olfactory gene variants. A recent study looked at using smell tests to determine HLA variants.[ref]
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.[ref]
Asparagus Pee
Asparagus pee smell… half of you know what I’m talking about.
More than half of the 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 it. The study found that 8% of the participants’ urine did not have a detectable asparagus odor. The ability to smell the asparagus pee smell is much stronger in those who carry the A allele rs4481887 (see the genotype report below..
Odor Receptor Genotype Report:
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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.
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