What the Nose Knows - Avery Gilbert [111]
Cultural factors—the favorite explanation of academic researchers—certainly play a role in odor preferences. But cultural explanations don’t go too far in explaining the extensive differences between people within the same culture. Biological factors, which receive surprisingly little attention, may account for much of this variation. For example, certain specific anosmias—the inability of a person with otherwise normal smell to detect a specific type of molecule—have a biological basis, namely the lack of a receptor for the molecule in question. There are a couple of dozen specific anosmias, but they account for merely a fraction of the total variation in odor perception.
The key to the mystery may reside more broadly in the human genome. A tantalizing possibility is that your olfactory receptor genes determine how you smell the world, and why you smell it differently than other people. Everyone has roughly 350 olfactory receptors, but not necessarily the same 350 as the next person. In addition, the gene for a given receptor can show subtle variation in DNA sequence from person to person.
The science of genetics links genotype (a person’s DNA profile) to phenotype (a person’s physical and mental traits). Several laboratories around the world are exploring the genetics of odor perception. Their first challenge is to characterize a person’s odor perception phenotype—in other words, to measure the sensitivity to, and preference for, a wide range of smells. The next step is to use DNA analysis to establish a person’s odor receptor genotype. Researchers expect that people with similar phenotypes have certain genetic traits in common. For example, people who like musk, hate grape, and are indifferent to patchouli may have certain odor receptor variants in common, and these biomarkers could become the basis of the in-store perfume preference diagnostic.
The first step toward a functional genomics of olfaction has already been taken. Researchers at Rockefeller and Duke Universities have discovered that variations in one odor receptor gene are responsible for differences in how people perceive the molecules called androstenone and androstadienone. These genetic variations, known as single nucleotide polymorphisms, have the effect of muting the intensity and unpleasantness of these two smelly molecules. It’s astounding that such tiny mutations can have such major consequences for odor perception. Yet this is just the tip of the iceberg—we can expect many more examples in the years ahead.
Knowing the link between genes and odor perception will profoundly change how we think about smell. Pavlovian learning and Proustian remembering will have to share the stage with biology. The discovery of biological markers for scent preference would revolutionize the design and marketing of fragrance. Instead of making products that appeal to the market as a whole (and satisfy no one in particular), perfumers could target scents to biologically defined market segments. A perfumer designing something for the musk-loving, grape-hating, patchouli-indifferent audience will have a tremendous advantage over a competitor working with the old hit-or-miss method.
THE GENOMIC AGE of odor perception will be exciting. We will be able to alter odor perception at a fundamental biological level—enhancing the response of a receptor, for example, or blocking it from working at all. These molecular-level interventions could lead to new types of consumer products. Imagine a long-lasting nasal spray for the medical staff in hospitals and nursing homes. One squirt at the start of a shift would knock out the ability to smell the ammonialike notes in urine, but leave the perception of other odors unchanged. The product would work by stopping a specific class of molecules from triggering a sensation. A narrow-range odor blocker like this would make the hospital a more pleasant place to work; and happier staff