Ghosts in Your Genome?

The ghosts in your genome may be DDT (sprayed liberally in neighborhoods in the 1950s) or other chemical pollutants encountered by your parents or grandparents; or you may be passing along such ghosts from chemicals you encounter today. In new research at Washington State University the effects of environmental toxins were passed down to offspring, and even to second generation (grand-offspring if you will) of lab rats exposed to chemicals including jet fuel, plastics and the pesticide DEET found commonly in bug sprays applied to skin. The impact of the exposure was greatest in the first phase of pregnancy when gender is determined.

Earlier research from this team showed similar effects from pesticides and fungicides, but this is the first to show generational effects from a variety of environmental toxins. "We didn't expect them all to have transgenerational effects, but all of them did," Michael Skinner, the molecular biologist leading the research, told the technology website Gizmodo.

The study was funded by the U.S. Army to study pollutants that troops might be exposed to. Skinner and his colleagues exposed pregnant female rats to relatively high but non-lethal amounts of compounds widely encountered by the general public, and tracked changes in three generations of offspring. The results were disturbing.

Researchers found distinct epigenetic signatures in the animals' sperm that acted as biomarkers of ancestral exposure to toxins.

Toxins had a powerful effect on reproductive health. The researchers saw female offspring (and second generation offspring) reaching puberty earlier (particularly associated with exposure to plastics), increased rates in the decay and death of male offspring sperm cells and lower numbers of female offspring ovarian follicles that later become eggs. But there were also major implications for what is known as epigenetics, the science of how and why genes are expressed in individuals. The animal's DNA sequence remained unchanged, but the chemical compounds changed the way genes turn on and off, opening new ground in the study of how disease develops.

While toxicologists generally focus on animals exposed to a compound, Skinner’s work further demonstrates that diseases can also stem from older, ancestral exposures that are then mediated through epigenetic changes in sperm. In a fascinating twist, the researchers found distinct epigenetic signatures in the animals' sperm that acted as biomarkers of ancestral exposure. In otherwords, they werere able to identify what specific toxins an animals' ancestors had been exposed to by looking at the genomic features of its sperm. 

The timing of the initial chemical exposure had an effect on its impact. In his paper, Skinner writes, "Gestating women in the first half of pregnancy would be the population most sensitive to exposures of environmentally induced epigenetic transgenerational inheritance." In other words, pregnant women need to be especially vigilant during the first trimester when their babies' reproductive system is under construction.

The authors posit that their study is a signpost toward understanding the early life basis of adult onset disease. Virtually all of our rising chronic diseases--diabetes, obesity, asthma, cardiovascular and inflammatory bowel diseases--are thought to be influenced by epigenetic changes from environmental exposures; knowing such changes can take place in ancestral exposures before a person is even born will surely help lead the way to a healthier future for the planet.

Read the study here.