Some men smell of vanilla while others smell of urine, but it is not always down to personal hygiene or ice-cream tainted Cologne. It turns out that a single gene is responsible for changing the way our noses perceive the smell of androstenone, a derivative of testosterone, and a potent ingredient of male body odor.

For most of us, urine smells of urine and vanilla smells of vanilla. But androstenone can have either scent depending on your genes. Most people describe its smell as at worst a foul odor reeking of stale urine or strong sweat but a rare few get a whiff of androstenone and are reminded of the sweet and pleasant smell of vanilla. Some people cannot smell androstenone at all.

Androstenone, found in higher concentrations in the urine and sweat of men than of women, is used by some mammals to convey social and sexual information, and the ability to perceive androstenone's scent may have far-reaching behavioral implications for humans.

Now, researchers at Rockefeller University, New York, and Duke University, North Carolina, have discovered that the variability in our ability to smell androstenone is due in large part to genetic variations in a single odorant receptor called OR7D4. The team studied 400 participants and made them sniff some 66 odors at two different concentrations and asked them to rate the pleasantness and intensity of each odor. The researchers also collected DNA from blood samples. With this large dataset the team could tie together differing scent perceptions with variations in the genetics underlying differences in olfactory receptor proteins.

Although it has long been suspected that the ability to perceive the odor of androstenone is genetically determined, this study is the first to identify variations in a single gene that account for a large part of why people perceive androstenone's scent so differently.

"Since some mammals clearly use androstenone to communicate sexuality and dominance within a social hierarchy, it's intriguing to think whether the same thing may happen in humans," team member Leslie Vosshall explains, "If so, what happens to humans who can't get the signal because they have the non-functional copy of the gene? Or the hyperfunctional one? What could be the social and sexual implications of this on one's perception of the smell of fellow humans?"

Nature, 2007, in press http://dx.doi.org/10.1038/nature06162

http://vosshall.rockefeller.edu/