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That Stinky Scent

After eating asparagus, some people can detect an odor in their urine, but others cannot. In a special holiday article appearing in the BMJ, researchers from the Harvard TH Chan School of Public Health report on a genome-wide association study they conducted to uncover loci linked to the inability to smell this smell.

The smell is typically likened to rotten or cooked cabbage or skunk, Marcia Pelchat, a food scientist at Monell Chemical Senses Center, tells NPR's Angus Chen, who can't smell it. Pelchat, who was not involved in this study, adds that when she conducted her own work, the smell in the bathroom "brought tears to my eyes."

In their study of nearly 7,000 people of European descent from the Nurses' Health Study and the Health Professionals Follow-Up Study, Harvard's Lorelei Mucci and her colleagues found that about 60 percent of the participants said they couldn't smell this asparagus-urine odor. They linked 871 loci, mostly on chromosome 1 where there are many olfactory receptor 2 family genes, to this asparagus anosmia.

Further analysis enabled them to home in on three independent markers: rs13373863, rs71538191, and rs6689553. The rs6689553 marker is in strong linkage disequilibrium with two missense mutations in OR2M7, while rs13373863 could be tagging an OR2L3 missense mutation, the researchers note. Both OR2M7 and OR2L3 are suspected to have roles in G-protein receptor and olfactory receptor activity, Mucci and her colleagues say.

"Future replication studies are necessary before considering targeted therapies to help anosmic people discover what they are missing," she and her colleagues write.