Super sensitive to BO? Maybe blame your genes

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Genes may partly determine how strongly you smell the noxious aroma of a stinky armpit, according to new research.

Likewise, your genetics influence how you perceive the smell of galaxolide, a synthetic “woody” musk used in perfumes and cleaning products, according to a new study published Thursday (February 3) in the journal PLOS Genetics. The new research reveals that people perceive these familiar scents as more or less intense depending on which versions of specific genes they carry. These key genes code for odor receptors, specialized proteins in sensory cells that detect odorous compounds.

Subtle differences between your scent receptors and someone else’s can lead to drastic differences in how you each perceive various scents, said study co-lead author Joel Mainland, an associate member of the Monell Chemical Senses Center in Philadelphia and Adjunct Associate Professor. in Neuroscience at the Perelman School of Medicine at the University of Pennsylvania.

Related: Genetics by the Numbers: 10 Tantalizing Stories

“You have about 400 [types of odor] receptors, but you smell a lot more than 400 odors,” Mainland told Live Science. That’s because, rather than each odorant compound activating just one olfactory receptor, a single odorant compound can activate a multitude of receptors. So when you take a whiff of something, a number of scent receptors light up in your nose.The brain then notices which combination of receptors is active and decodes this information to identify the delicate scent of a rose. , or the pungent stench of BO

Because our perception of smell begins at our receptors, “which set of receptors you have has a huge impact on what you can smell, and so any variation in that set of receptors will change how you smell”, Mainland said.

In their new study, Mainland and his colleagues explored how people’s genetics shape the scent receptors they carry and, therefore, dictate how they smell. Genes and odor receptors aren’t the only factors that shape our perception of odors, but they both play very influential roles, Mainland noted.

Several of the paper’s authors are based in China, including co-lead author Sijia Wang, professor and group leader at the Chinese Academy of Sciences; these authors had previously collected genetic data from a large population of Han Chinese, who belong to a major ethnic group in China. From this population, the researchers analyzed data from 1,000 people between the ages of 18 and 55. They also repeated the study in a smaller cohort of about 360 ethnically diverse people in New York City, to see if their findings carried over to different populations.

The team analyzed each participant’s entire genome and asked each person to take a smell test in which they rated the intensity and pleasantness of different smells on a 100-point scale. These odors included synthetic musk galaxolide, as well as a compound called trans-3-methyl-2-hexenoic acid (3M2H), which can be described as the characteristic smell of a stinky armpit.

Many other odorous compounds also contribute to the overall stench of body odor — about 120 compounds in all, the authors noted in their report. But among these, 3M2H is considered an “impact smell”, which means it carries the characteristic smell of BO

With the genomic and odor perception data in hand, the team began looking for patterns between the participants’ genetics and their odor perceptions.

They identified gene variants, i.e. spots in the genome that differed between people at the level of unique base pairs, which were linked to differences in smell test data, said co-first author Marissa Kamarck, a PhD candidate at the University of Pennsylvania and a researcher in the Mainland lab at Monell. (Base pairs are the individual “rungs” of the twisted ladder of DNA.)

These tests highlighted the genes for two odor receptors, called OR4D6 and OR51B2, as critical for the perception of galaxolide and 3M2H, respectively. Before this study, scientists didn’t know which odorous compounds activated these receptors, Mainland said.

In the OR4D6 gene, the team spotted two intriguing single nucleotide polymorphisms (SNPs), which are single “letter” changes in DNA. These two SNPs often appeared together, but not always. People who wore either SNP or both SNPs rated the smell of galaxolide as significantly less intense than people who wore neither SNP.

“The newly discovered galaxolide receptor (OR4D6) may be essential for odor perception,” Kamarck wrote in a tweet about the study. “Most people who had two copies of a genetic variant of the receptor” – one from each parent – “were no longer able to smell galaxolide!”

In contrast, people who carried a specific SNP in the OR51B2 gene perceived the armpit stench, namely 3M2H, to be more intense than people without that SNP, the team found. Nearly 60% of the sample population carried this more sensitive version of the gene.

Looking ahead, Kamarck said she is interested in determining whether variants of the OR4D6 gene, for galaxolide, also affect the perception of other musks. Musks fall into five distinct structural classes, which means that the different classes are very different from each other at the molecular level. However, all five classes of musk smell similar – the scents are often described as “sweet, warm, and powdery,” the authors wrote in their report. The team wants to determine whether variants of the OR4D6 gene affect the perception of other musks in the same class as galaxolide, as well as the other four classes.

There’s also the question of when these different genetic variants first appeared and what their appearance can tell us about the evolution of the human sense of smell, Mainland said. Based on previous research and the new study, the team found clues that, in general, the sense of smell of humans and other primates has deteriorated over time, in part due to mutations in the key genes of odor perception. However, this is not necessarily true for all genes, such as OR51B2, so the team wants to study this in more detail.

Originally posted on Live Science.

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