What did the patients have in common? The scientists noticed each had a mutation in the SELENBP1 gene. They wanted to figure out if this gene was causing the smell, so they knocked it out of some lab mice. All of these mutant mice had way higher levels of these stinky sulfur compounds in their blood plasma—it looked like the mutation in the SELENBP1 gene could have been causing the stink.


These observations reveal that maybe SELENBP1 produces an enzyme responsible for breaking odorous molecules down. “The function of SELENBP1 might possibly be keeping the breath methanethiol concentration low,” the scientists write in the paper, “thus enabling the human nose to detect foul smells from environmental volatile sulfur compounds” instead of the human’s own foul breath.

There’s more than just bad breath at stake here—the scientists speculated further, based on past research on SELENBP1, that it could play some role in suppressing tumors. They point out that dogs can smell some tumors, and perhaps they’re smelling the compounds not broken down by the SELENBP1 proteins. Again, just speculation here, but maybe they’ve found another gene that plays a role in cancer development, too.

This is just one paper, humans aren’t mice, and the research certainly isn’t tied up with a bow yet, given how complex the human body is. But if you’re about to kiss someone whose breath smells like cabbage, maybe ask if their SELENBP1 gene is okay.

[Nature Genetics]