While smarter, more effective medical care is the bright side of epigenetic research, there’s a dark side — albeit a controversial one.
Genetic scientists have long believed that epigenetic modifications to DNA are not heritable in humans — meaning they can’t be passed from one generation to the next. It was thought that, like a car wash, DNA is rinsed of its accumulated epigenetic detritus as it passes from parents to offspring. But Skinner and some other scientists believe that certain epigenetic adaptations can be passed from one generation to the next, and that the inheritance of these epigenetic changes could help explain the rise in obesity, diabetes, and other heretofore uncommon diseases.
For example, Skinner’s research has identified epigenetic mechanisms through which exposure to the insecticide chemical DDT changes gene expression in ways that can be passed from parent to offspring, and that may contribute to the development of obesity in successive generations. “DDT exposure doesn’t cause obesity, but it promotes susceptibility to obesity,” he says. “In the 1950s, almost every pregnant woman in America was exposed to DDT, and now, three generations later, we have a 45% obesity rate.”
While DDT is now banned in the United States, Skinner says that glyphosate — one of the most commonly used herbicidal chemicals in the country today — has also been linked to disease-promoting transgenerational epigenetic changes. “So, glyphosate exposure today probably won’t affect us, but our grandkids may have elevated disease risks,” he says.
Not all scientists buy into the idea that epigenetic adaptations are heritable. “The evidence for transgenerational epigenetic inheritance… is not (yet) conclusive,” argued the author of a recent review of the research in the journal Nature Communications. Summarizing the view of many geneticists, he wrote, “For now, I remain skeptical.”
But others say the experimental evidence in animals is compelling, if not conclusive. “If you change a female rat’s diet, you can see changes that are passed down for two generations,” says David Nielsen, an associate professor and director of the Toomim Laboratory for Psychiatric Genetics at Baylor College of Medicine. There’s also evidence that the grandchildren of people who endure lengthy food shortages or starvation may be more susceptible to metabolic disease.
“The diseases you have today may be due to your grandparents’ environmental exposures,” Skinner says. Likewise, the choices a person makes today — the foods they eat or avoid, the drugs they experiment with — could promote epigenetic changes that affect the health of their kids, their grandkids, and successive generations. While scientists are still teasing apart and debating the role of epigenetics in inherited risk, Skinner says that what we know already should inform the choices we make. “We need to be much more conscientious today about what we do to our bodies and our environment,” he says.