How a grandmother's exposure to toxins may affect her grandchildren and great-grandchildren

Traditionally, the belief held by the scientific community and beyond was that DNA was responsible for transmitting biological information from one generation to the next via genes, and this is true.

Sometimes, random mutations occur and change a gene’s message and the altered message gets passed down to the offsprings. Epigenetics has posed an alternative, additional way that genes can be changed, through parts of the DNA that interact with the environment, and when insulted, become epimutations.  

In 2005, Michael Skinner and colleagues in his lab discovered that third and fourth generation descendents of a pregnant rat exposed to fungicide had abnormally low sperm counts and that the condition w​as n​ot a result of a change in their inherited DNA (Smithsonian 2016).

They  repeated the experiments again and again,with different chemicals and substances known to be linked to prostate, kidney, ovarian, and immune system diseases, and consistently observed similar results - diseases showed up in offsprings of exposed mothers many generations later. This discovery brought forth a new way of thinking about the possible long-term health problems of exposure to environmental chemicals and highlighted the dangers of toxic exposures during pregnancy.  We have tended to think of environmental pollutants being dangerous to adults and children, and perhaps dangerous to a fetus being carried by an exposed mother.  But the idea that exposure to a chemical in a grandmother would be passed down to grandchildren yet to be born?  This is a pretty important hypothesis for anyone interested in reproductive health, or indeed, health of any kind.

The biochemistry behind transgenerational epigenetics is complex. Skinner’s studies found that as toxins are absorbed into the body, they alter certain molecules that attach to cells that eventually become eggs or sperm, which are then passed down to future offsprings. These molecules interfere with DNA functions and persist through generations and each time opens up the pathway to the same diseases.

In Skinner’s words, “what your great-grandmother was exposed to could cause disease in you and your grandchildren.” In other words, when a pregnant woman is exposed to potentially toxic substances during pregnancy, it can go on to affect not just her children, but her descendents further down the line as well.

On the bright side, these findings could potentially help in new medical diagnostics where doctors would look at a patient’s molecular patterns early on in life to determine his or her risk of developing certain diseases.

In 2012 Skinner's team reported that "exposure of pregnant rats to either the pollutant dioxin, jet fuel, insect repellent, or a combination of bisphenol A (BPA) and phthalates—chemical components of plastics in food containers and tooth fillings—induce a variety of heritable disorders in fourth-generation descendants, such as pubertal abnormalities, obesity, and diseases of the ovaries, kidneys and prostate."

These discoveries have not come without controversies. Some say that the doses of chemicals Skinner uses in his studies are many more times that of what people would ever be exposed to and therefore his results are not relevant to humans. Skinner, however, responds by saying that it had not been his goal to perform risk assessment for chemicals, but rather to provide another possible explanation for transgenerational effects and how genes and the environment interact.