Are PTSD, Fears, and Phobias Heritable?

In the evolutionary perspective, our offspring should have a higher chance of survival than ourselves and our ancestors. More favorable genes will be expressed, while those that will prove a threat to one’s survival will be silenced. This is seen everyday in the animal kingdom. Females will choose their mate based on competence, strength, and resources. Aside from physical characteristics, are fears, phobias, and the risk of developing post-traumatic stress disorder (PTSD) also being passed down to the next generation to aid their survival?

Epigenetics is the study of DNA modifications in response to changes in the environment, whether it is to boost or silence the expression of one gene. As a result, the offspring would only express “useful” genes that would heighten their chances of survival. An example would be the Dutch famine in 1944. Food supply was blocked to the Netherlands by the Nazis, resulting in the deaths of 20,000 people and a generation at risk for obesity and diabetes. Pregnant women who survived the famine gave birth to babies who would grow up to have a higher average weight and levels of LDL cholesterol. These individuals had the PIM3 gene, a gene responsible for metabolism, permanently silenced. These fetuses had their genes indefinitely altered to have a better chance of survival in an environment that lacked food, which is a mark of resilience. However, a change that was meant to have prolonged their life expectancy turned out to have caused these individuals to die at an increased rate. 

How does this example translate to our inheritance of fears and phobias? Humans are born with two innate fears: the fear of falling and the fear of loud sounds. However, we may also develop learned fears from our parents or inherit them. For example, children may be afraid of spiders or snakes because they could be venomous. Another example is the multiple studies done on mice who receive an electrical shock paired with a particular scent, only to then develop a fear of the scent. The offspring of these mice will also show a heightened stress response to that scent. It can be hypothesized that such fears are inherited in order to provide our offspring with a warning signal to know when something is threatening and to stay away, thus increasing their chances of survival. 

Studies have also been done on Holocaust survivors and their descendants. One study done by Rachel Yehuda in 2016 has shown that survivors had higher levels of stress hormones than other Jewish people who resided outside of Europe during World War 2 or had escaped the Holocaust. The children of survivors were also found to have higher stress hormones compared to their counterparts. This alteration in their genetics may be a benefit or another tragic consequence of the Holocaust, as some children may be more resilient to stress and challenges, while others may be more susceptible to depression and anxiety disorders. Yehuda attributes this change to epigenetic tags on a gene responsible for “the regulation of stress hormones, which is known to be affected by trauma.” (Thomson) 

Interestingly, epigenetic tags are meant to be erased before an egg is fertilized, but some tags may remain in the genome. It is not clear which tags are not erased, or if they are purposefully not erased. The risk for post-traumatic stress disorder (PTSD) may also be attributable to one’s DNA. The genetic basis for PTSD is also unclear, as individuals have different responses to traumatic events. Studies have been done on prisoner of war survivors, for example. Children born to survivors after they became a prisoner of war showed a higher mortality rate compared to children born to men before they became a prisoner of war. 

Although the children may not have directly experienced their parents trauma, the scars still linger. Epigenetic changes may prove an advantage in some cases, but in other cases, they can actually jeopardize an individual’s survival and take a toll on their mental health. It is important that we recognize how our experiences may impact our descendant’s physical and mental health so that we may address their susceptibility and not intervene when it’s too late. 

References:

Carey, Benedict. “Can We Really Inherit Trauma?” The New York Times, The New York Times, 10 Dec. 2018, www.nytimes.com/2018/12/10/health/mind-epigenetics-genes.html.

Henriques, Martha. “Can the Legacy of Trauma Be Passed down the Generations?” BBC Future, BBC, 26 Mar. 2019, www.bbc.com/future/article/20190326-what-is-epigenetics.

Nedelman, Michael. “PTSD Risk May Be Inherited through DNA.” CNN, Cable News Network, 25 Apr. 2017, www.cnn.com/2017/04/25/health/ptsd-trauma-genetics-study/index.html.

Thomson, Helen. “Study of Holocaust Survivors Finds Trauma Passed on to Children's Genes.” The Guardian, Guardian News and Media, 21 Aug. 2015, www.theguardian.com/science/2015/aug/21/study-of-holocaust-survivors-finds-trauma-passed-on-to-childrens-genes.

Tom Spears, Ottawa Citizen. “Can We Inherit Fear? Welcome to the Mind-Bending Science of Epigenetics.” Ottawa Citizen, Ottawa Citizen, 8 Sept. 2017, ottawacitizen.com/technology/science/can-we-inherit-fear-and-other-mind-bending-questions-being-raised-by-science.

Zimmer, Carl. “The Famine Ended 70 Years Ago, but Dutch Genes Still Bear Scars.” The New York Times, The New York Times, 31 Jan. 2018, www.nytimes.com/2018/01/31/science/dutch-famine-genes.html?auth=login-email&login=email