Odorant receptors are the largest gene family in the human genome, and they differ enormously between people. The result is that two people can meet the same molecule and only one of them smells anything at all.
Almost everything on this site describes a probability being nudged. Smell is the exception. A change in an odorant receptor does not make a disease slightly more likely — it changes what the person perceives. Two people walk past the same plant, the same cheese, the same open bottle, and one of them registers a smell that for the other is simply not there.
This happens because of how the sense is built. Detecting odours is not one mechanism but hundreds: the odorant receptor genes are the largest gene family in the human genome, several hundred of them, each responsible for a slice of chemical space. When one is altered, the effect is narrow and specific rather than general. That is the origin of specific anosmia — a normal sense of smell with one particular molecule missing from it.
Taste and smell are separate senses with separate receptors, separate nerves and separate destinations in the brain. The tongue reports five things: sweet, sour, salty, bitter and umami. Everything else you experience while eating — the difference between an apple and an onion, between coffee and cocoa, between one wine and another — arrives through the back of the nose from the food already in your mouth, and is smell.
This is why food goes flat during a heavy cold, and it is why loss of smell is so disorienting: people describe it as losing the ability to taste. Anything that changes what you can smell therefore changes what eating is like, which is what connects this page to the metabolic and nutritional pages elsewhere on this site.
Something worth noticing about that list: in each case the associated variant sits in a gene that has a direct, known job in smelling. That is not how most genetic findings work. Elsewhere on this site the strongest association for atrial fibrillation lies in a stretch of DNA 150,000 letters away from the nearest gene, and the best-known obesity variant turns out to act on two neighbouring genes rather than the one it sits inside. In smell, the finding tends to land on the receptor itself.
A related trait sits on the other side of this: rs17822931 in ABCC11 determines earwax type and underarm odour — not what a person detects, but what they emit.
Nothing clinical. There is no treatment that follows from knowing this, and no health decision that should change. What it offers is an explanation for something people notice about themselves and are rarely able to account for — and, unusually for genetics, one that can be checked against your own experience the next time you open the fridge.
Receptor architecture. Human olfaction is mediated by several hundred functional odorant receptor (OR) genes, the largest gene family in the genome, together with smaller families including the trace amine-associated receptors (TAARs). Each receptor responds to a set of molecular features rather than to a single compound, and each odour is encoded by a combination of receptors. Loss or alteration of one receptor therefore produces a narrow perceptual deficit — a specific anosmia — rather than global hyposmia. The family also carries an unusually high burden of segregating pseudogenes and functional variation between individuals, which is the structural reason perceptual differences in this sense are both common and large.
TAAR5 rs41286168. TAAR5 is a trace amine-associated receptor responsive to trimethylamine. In a study of odour perception and naming in 9,122 individuals of Icelandic ancestry (Current Biology 2020; PMID 33035477), carriage of the variant allele was associated with reduced rated intensity of the fish odour and greater difficulty naming it (p = 6 x 10-15 and 5 x 10-17 in the reported analyses). The association was independently seen for fish-odour identification in an 18,880-participant meta-analysis of olfactory identification (2025; PMID 40593737). The variant allele is uncommon, so the homozygous phenotype is rare.
OR2M7 rs4481887. Associated with the ability to detect the sulfur-containing metabolites excreted in urine after asparagus consumption, in a web-based participant-driven association study (PLoS Genetics 2010; PMID 20585627); odds ratio 1.67 per copy, p = 7 x 10-24. Production of the metabolites appears close to universal; the trait is one of detection.
UGT2A1/UGT2A2 rs7688383. In a genome-wide association study of self-reported loss of smell or taste during COVID-19 (Nature Genetics 2022; PMID 35039640) comprising 33,336 cases and 16,257 controls of European ancestry with Latino replication, the variant allele was associated with increased odds of the symptom, odds ratio approximately 1.11-1.12 per copy. UGT2A1 and UGT2A2 are expressed in olfactory epithelium and are implicated in the metabolism and clearance of odorant molecules, providing a plausible mechanism for a specifically olfactory effect.
Retronasal olfaction and flavour. Gustation is limited to five qualities transduced by taste receptor cells and carried by the facial and glossopharyngeal nerves. Flavour is a multimodal percept combining gustation, retronasal olfaction, somatosensation (texture and temperature) and trigeminal chemesthesis (pungency, cooling). The olfactory contribution dominates discrimination between foods, which is the basis of the common report that food is tasteless during nasal congestion and of the frequent patient description of olfactory loss as loss of taste.
Clinical status. No variant described here has diagnostic or therapeutic application. Persistent olfactory loss, whether following infection or otherwise, warrants clinical assessment on its own merits and independently of genotype — it can also be an early feature of several neurodegenerative conditions, which is a reason to evaluate it rather than to attribute it.
What a 23andMe/AncestryDNA export or raw VCF can and can't tell you about Smell Perception and Specific Anosmias comes down to these specific, well-studied positions — not a diagnosis.
A normal sense of smell with one particular molecule missing from it. Because odours are detected by hundreds of different receptors, a change in one removes one narrow ability rather than degrading smell in general. Most people have at least one and never find out.
Yes, literally. The tongue reports five qualities — sweet, sour, salty, bitter and umami. Everything that distinguishes an apple from an onion reaches you through the back of the nose from the food in your mouth. That is why food goes flat during a cold, and why people who lose their sense of smell usually describe it as losing their sense of taste.
Because the variant is usually in the receptor itself. Most complex traits produce associations in regulatory stretches of DNA whose mechanism is unknown — the strongest atrial fibrillation signal sits 150,000 letters from the nearest gene. In smell, the gene that comes up is the gene that does the smelling.
Not on its own. The UGT2A1/UGT2A2 variant shifts the odds of that symptom modestly; it does not determine who gets it or predict recovery. Smell loss that persists is worth having assessed clinically regardless of genotype.
Nothing medical. It explains something you may have noticed about yourself and could not account for — why a smell others complain about does not reach you, or why one does reach you and nobody else seems to mind.
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