Factors such as age, nutritional habits, psychological stress, physical activity, working habits and substance abuse can trigger changes in gene expression (Alegría-Torres, 2011). These changes in gene expression, epigenetics, happen all the time in the natural world.
For example, two identical twins, born with the exact same DNA sequence may not express the same genes. One may develop an illness while the other does not. Even diseases that are highly heritable are not guaranteed to develop in both identical twins. If your identical twin has schizophrenia, you have a 53% chance of developing schizophrenia (Roth, Lubin, Sodhi, & Kleinman, 2009). But If you have the exact same DNA, and schizophrenia is genetically heritable, why do you not have 100% chance of developing the same disorder?
Our environment and lifestyle impacts our gene expression.
For better or for worse, the DNA we are born with does not predetermine our health. Life experiences and environmental factors play an important role in who we become.
For people facing mental health challenges, and for therapists providing treatment, understanding that DNA is not destiny can help shape treatment.
Epigenetics and inherited trauma; an experimental manipulation
In a recent study, researchers showed how interpersonal early life stress can impact second and third generation offspring. Researchers exposed mice offspring to early and unpredictable separation from their mother from day 1 to 14. The mother was subjected to stress and the offspring were physically restrained or placed in cold water. This kind of situation is classified as chronic and unpredictable stress.
The offspring displayed depressive symptoms, as was expected. However, the interesting result of this study was what occurred with the second and third generation offspring. The next generations were raised normally. However, the later generations also displayed abnormally high rates of depressive symptoms.
To factor out the effects of being cared for or being in a group with the first generation traumatized mice, the researchers inseminated the sperm of the past traumatized males into the eggs of non traumatized mice. The results were the same, offspring raised normally with non-traumatized mothers still displayed abnormally high rates of depressive symptoms.
While the mechanism of passing trauma through generations is unknown, it is thought that the the dysregulation of short RNA’s occurs as a result of an overexposure to stress hormones circulating in the body
The results are thought to be relevant for humans as well. Children exposed to early and ongoing trauma are more likely to develop a variety of physical, behavioral and emotional disorders. In addition to emotional and mental disorders, sufferers of childhood abuse are also at increased risk to develop physical health problems such as heart disease, obesity, and cancer (National Human Genome Research Institute).
Is fear heritable?
Puzzled by the problems in inner city communities where problems such as mental illness, drug addiction and other problems seemed to occur over generations, Kerry Ressler became interested in researching the intergenerational transference of risk. The Ressler lab investigates the genetic, epigenetic, molecular and neural circuit mechanisms that underlie fear. An experiment with mice revealed that memories of pain can be passed down to first and second generation offspring even though these offspring had never experienced the fearful stimuli.
In the study, small electric shocks were paired with a particular odor in male mice. After the situation occurred numerous times, the mice, when encountering the odor would tremble in fear even without the shocks. The first and second generation offspring of these mice displayed the same reactions to the odor, even though they had never experienced the electric shocks (Callaway, 2013).
So what does this mean? From these experiments we can see that the memory of significant trauma is passed down to the the next generation and even the generation after that. What happened to our grandparents and our parents seems to leave a memory in our physical beings.
The good news
Epigenetics is also affected by positive environmental influences. While we can see that trauma affects our offspring through the malleable process of gene expression, this new line of research is also showing that epigenetics can be reversed.
If male mice experience early trauma and then are placed in a nurturing environment they go on to develop normal behavior. Their offspring also develop normally. The conclusion of these studies, so far, indicates that early life stress can be reversed. At least some adults who seek out (and are able to attain) a nurturing and low stress environment can reverse the effects of past trauma. This is good news and should inform therapeutic approaches. It may not be necessary to rely as much on pharmaceuticals. Lifestyle changes and a supportive therapeutic relationship can go a long way to reversing trauma and preventing trauma from being passed down to the next generation.
Alegría-Torres, J. A., Baccarelli, A., & Bollati, V. (2011). Epigenetics and lifestyle. Epigenomics, 3(3), 267-277.
Bell, J. T., & Spector, T. D. (2011). A twin approach to unraveling epigenetics. Trends in Genetics, 27(3), 116-125.
Callaway, E. (2013). Fearful memories haunt mouse descendants. Nature, 1, 1-6.
Roth, T. L., Lubin, F. D., Sodhi, M., & Kleinman, J. E. (2009). Epigenetic mechanisms in schizophrenia. Biochimica et Biophysica Acta (BBA)-General Subjects, 1790(9), 869-877.
Franklin, T. B., Russig, H., Weiss, I. C., Gräff, J., Linder, N., Michalon, A., … & Mansuy, I. M. (2010). Epigenetic transmission of the impact of early stress across generations. Biological psychiatry, 68(5), 408-415.
By Fabiana Franco, Ph.D.