Ben Panko in Smithsonian:
Harvard researcher Sarah Coseo Markt and her colleagues were dining on steamed asparagus with Hollandaise sauce at a Swedish scientific meeting when they came across a critical research question. Asparagus, as you might know, has a reputation for imparting a sharp, sulfuric smell to people's urine shortly after they eat it. Later that evening, Markt and her supervisor, Harvard University epidemiologist Lorelei Mucci, experienced that truism firsthand. But surprisingly, several of their companions said they had experienced no unusual bathroom odor. Why not?
After returning to Boston, the pair decided to investigate the conundrum further. Luckily for them, they had access to surveys collected every two years by Harvard from thousands of men and women of European-American backgrounds. For the 2010 surveys, Markt and her colleagues added a question asking people to rate the following sentence: “After eating asparagus, you notice a strong characteristic odor in your urine.” Roughly 60 percent of the nearly 7,000 men and women surveyed said they had “asparagus pee anosmia,” or the lack of ability to smell asparagus-influenced urine. The diligent researchers then pinpointed the specific cluster of genes that controlled this ability, by comparing the genomes of the people surveyed to whether or not they were able to smell the asparagus-y urine. They found that a difference in 871 nucleotides—the letters that make up a DNA strand—on Chromosome 1 appeared to control whether or not one could “enjoy” the smell after a meal of asparagus. Markt’s research, cheerfully titled “Sniffing out significant 'Pee Values': genome-wide association study of asparagus anosmia,” ended up in this week’s issue of The British Medical Journal (BMJ), becoming part of a hallowed end-of-year tradition.