“Field” Work with Twins

Not all work at the Monell Center takes place within the confines of the Center’s Philadelphia-based laboratories. Long-term Foundation support helps provide the Center’s scientists with the flexibility to go beyond the lab to increase scientific understanding of the many ways that taste and smell influence human health and well-being.

On Saturday, August 4, 2018, 15 excited scientists rose before dawn, donned sunscreen, and drove from their Residence Inn in northeast Ohio to the nearby R.B. Chamberlin Middle School. Dew soaked their shoes as they walked the mile from the grassy parking area to a large paved square surrounded by white festival tents.

There, Monell Center behavioral geneticist Danielle Reed, PhD, waited with the contents of a large U-Haul truck that the group had carefully packed in Philadelphia the day before. Pallets of water, coolers of ice, boxes filled with tiny bottles of liquid, and hundreds of padded noseclips surrounded her.

The researchers leapt into action, setting up tables, chairs, and testing stations before the sun had burned away the morning mist.

Why in the world would 16 Monellians, both current staff members and also many ‘alums’, drive nine hours from Philadelphia to the middle of Ohio?

Because of the extraordinary festival held here each year: The Twins Days Festival.

Converging Twins

Twins and other multiples travel from across the United States and around the world to Twinsburg, Ohio for this unique event (the town’s name came first). Two thousand sets of twins and multiples regularly attend, from babies in strollers to giggling teenagers to seniors in their 80’s and 90’s. Most dress in identical clothes and costumes, adding to the surreal feeling of being surrounded by clones.

For the Monell researchers, the Festival is a scientific gold mine.

Twins serve as a natural experiment for studying the influence of human genetics on traits and disorders. Identical twins share 100 percent of their genes, while fraternal twins share roughly 50 percent (similar to any non-twin sibling pair). Knowing this, scientists can compare a trait of interest – be it physiological, behavioral, perceptual, or other – to determine the extent to which a person’s genes (“nature”) influence that trait relative to environmental factors (“nurture”).

For Monell Center scientists, keenly interested in understanding how taste and smell influence dietary choices, nutrition, and healthy eating, twin studies help establish the degree to which our individual taste and smell perceptions are inborn and how much can be attributed to experiential and other environmental factors.

For example, while eating too much sugar is often seen as a personal weakness, twin research suggests that our perception of sweetness is partially determined by our genetic makeup. Reed explains, “Just as people born with a poor sense of hearing may need to turn up the volume to hear the radio, people born with weak sweet taste may need an extra teaspoon of sugar in their coffee to get the same sweet punch.”

Doubling Scientific Contributions

Which brings us back to the Twins Days Festival.

Reed took her first trip to Twinsburg in 2002, and in 2009, her lab began regular annual trips, seeking to better understand the genetics of taste. Each year, her team administers hundreds of sensory tests to twin pairs to identify sensitivity (“How much sodium chloride does it take before you describe this solution as salty?”), discrimination (“Does this taste sour or bitter?”), and liking (“How pleasant do you find this fructose solution?”). The researchers also obtain DNA – via saliva samples – from each twin to be analyzed back in the Monell Center’s labs.

If the identical twins are more similar than the fraternal twins with regards to a specific perceptual response, it suggests a genetic component is involved. Scientists can then work to identify the genes responsible.

Easy enough, right? Not exactly. Reed and her team found themselves on a steep learning curve. “I always tell people that this is fieldwork in an actual field,” says Reed. “There are a lot of practical constraints to this kind of research, and we’ve run up against many of them over the years.”

For starters, the researchers must prepare all the materials ahead of time and transport them to Twinsburg. That’s no mean feat: in 2018, the Monell Center researchers worked for weeks before the Festival to prepare 12,600 tiny sample bottles (plus extras, just in case), filling them with different concentrations of sweet, salty, bitter, and other stimuli, and then capping each bottle by hand.

Then, there are the physical conditions of the testing environment. The Twins Days Festival takes place in the first week of August, and it’s often hot – sometimes brutally so. That means dehydrated subjects, who can have difficulty providing the saliva needed for DNA. One year, the team tested sensory responses to certain herbs, only to find the plants wilting and started to rot. Participants of course get cranky waiting for their turn to be tested. In sum, it’s a hot, busy, tiring two-day testing marathon.

However, the benefits far outweigh the challenges.

Recruitment can be an enormous hurdle in human research. Finding participants who fit a study’s criteria, much less getting them to your testing location, can be a struggle.

In contrast, twins at the Festival literally line up to take part in the Monell Center’s research. “The subjects are so engaged – it’s very rare to see that in human testing,” Reed says. Most inherently feel that their twin-ness is something special, and enjoy learning more about why science agrees.

Advancing the Science

The Monell Center’s ongoing twin studies – at Twinsburg and elsewhere – on the genetics of sensory responses have led to a number of publications. Many involve the metric of “heritability,” which geneticists use to describe how strongly genetic factors influence a given trait. One of the most widely cited is a 2012 paper that describes taste heritability: sweet, salty, sour, bitter, and alcohol tastes, as well as those herbs that fared so poorly in the heat: cilantro and basil. The findings establish that many aspects of flavor perception are at least partially influenced by genetics. For example, liking for cilantro relates to three different gene variants, which could explain the wild differences between people’s attitudes toward the herb.

Knowing how genes contribute to flavor perception and dietary choices will help guide strategies to promote healthier eating. For instance, if we can understand why some people have weaker sweetness perception, we might be able to adjust this attribute so we could reduce the amount of sugar in foods. On another front, understanding the genes that underlie individual differences in bitter perception may extend the concept of personalized medicine to increase pharmaceutical compliance by helping to identify formulations that a given patient will accept.

In addition to ‘standard’ taste and smell sensory testing, Reed often includes additional experiments in the test battery. In fact, many of those small bottles for the 2018 Festival contained milk for a study asking how well people can distinguish the taste of high-fat from low-fat milk. It’s a surprisingly difficult task, but is it related to a person’s genetic make-up? Reed doesn’t know; that’s why they brought the milk along.

Another 2018 study recruited pairs where one twin had undergone treatment for cancer, with other twin serving as a real-world control. This project asks whether cancer therapies impact the survivor’s sense of taste in the long term. The findings potentially could help improve patient dietary and nutritional care after cancer treatments.

On Sunday, August 5, 2018, after they tested their last participant on the second day of the Festival, the weary researchers packed up the saliva, the consent forms, the fans, the extension cords, and all the other items they brought from Philadelphia, and trudged back to the truck. Exhausted but elated, they discussed the past two days, and, even before they left the grounds, began to brainstorm how to improve things for next year.