For many years we have understood that genetics influences our risk of disease and mental health problems. For example, we know that over half of cancers involve a missing or damaged p53 gene, and recently, a large-scale analysis identified ten genes directly linked to schizophrenia.
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Additionally, we understand that external factors (also known as environmental factors) also play a role in illness. For instance, exposure to cancer chemical substances, such as those found in cigarettes, has been proven to cause cancer, and recently, exposure to air pollution has been linked with an increased risk of various mental health illnesses, including depression.
Genes are inherited, so we know that the risk of mental and physical health problems can be passed down. Exposure to external factors, however, cannot be inherited. A person who smokes, for example, may increase their chances of cancer via exposure to chemicals in cigarettes; this exposure is a unique experience of the individual and causes damage to their body that is not inheritable. If someone were to lose a leg in a road traffic accident, their children would not inherit this affliction.
However, recent research has revealed that adverse life experiences can be recorded and passed down through the genes. Groundbreaking research looking into the children of people who had survived concentration camps highlighted the possibility that trauma can be passed on through alterations to our genetic information. This research, while criticized, has been supported by further research on other groups who have suffered trauma, including prisoners of war and people who have been enslaved or have been the victims of genocide. A growing body of research suggests that trauma can alter our genes, effectively being passed down from generation to generation.
Epigenetics: trauma changes how genes are expressed
The process of epigenetics is different from altering the code itself (e.g., through deletion, substitution, or insertion) and refers to the readability of the genetic code. Chemical tags are attached to our genetic code that determines how it is expressed. The phenotype can be altered by altering these tags without changing the genotype. These tags can be passed down to the next generation. This means that events in a person's life can be passed down regarding how their genes are expressed.
People who have experienced trauma are at risk of epigenetic changes due to the extreme situations they have had to endure. We know that toxic stress, often induced by trauma, is a major cause of epigenetic changes, which can lead to various negative health outcomes.
Research has shown that the sons of men who were prisoners of war had an 11% higher mortality rate than the sons of veterans who were not prisoners. This difference in mortality could not be explained by other factors such as the father's socioeconomic status, the son's job, or marital status. The researchers found that the increase in mortality was mostly attributed to higher rates of cerebral hemorrhage, and there was also an increase in the risk of death from cancer.
Another study found that epigenetic changes were observable in children of Holocaust survivors. These changes were on a gene linked with cortisol, known as the stress hormone. While the study was criticized for its small sample size and investigation of only one generation, other research groups have also found epigenetic changes in the children of people who have experienced trauma.
For example, researchers have found NR3C1 epigenetic modifications associated with PTSD in both mothers exposed to the Tutsi genocide and their children. These epigenetic changes were suggested to be linked with biological alterations of the HPA axis - which is implicated in managing stress, particularly toxic stress-induced negative health outcomes.
Another study found that the daughters of Dutch women who had fallen pregnant during the famine at the end of World War II were at an increased risk of developing schizophrenia, which is hypothesized to be related to the inheritance of epigenetic changes.
While there is reason to cast doubt on the likelihood that epigenetic changes can be passed on due to the fact that there is a rapid loss of DNA methylation on the paternal chromosomes once the sperm enters the egg, research at Cambridge University has shown that epigenetic tags survive this cleaning process.
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The consequences of passing down trauma
The possibility of passing down trauma to future generations is hugely significant. Even subtle changes to how the genetic code is expressed have significant implications for our physical and mental well-being. More research is needed to fully understand the nature of inheriting epigenetic changes as well as to understand how negative changes to gene expression, such as those linked with negative psychological or physical outcomes, can be prevented or managed.
Further research into this field will likely lead to a novel perspective on how we view mental health and may lead to better therapeutic options.
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- Helen Thomson. 2015. Study of Holocaust survivors finds trauma passed on to children's genes [online]. The Guardian. Available at: www.theguardian.com/.../study-of-holocaust-survivors-finds-trauma-passed-on-to-childrens-genes (Last Accessed January 2023)
- Martha Henriques. 2019. Can the legacy of trauma be passed down the generations? [online]. BBC. Available at: https://www.bbc.com/future/article/20190326-what-is-epigenetics (Last Accessed January 2023)
- Perroud, N. et al. (2014) "The Tutsi genocide and transgenerational transmission of maternal stress: Epigenetics and biology of the HPA axis," The World Journal of Biological Psychiatry, 15(4), pp. 334–345. Available at: https://doi.org/10.3109/15622975.2013.866693.
- Yehuda, R. and Lehrner, A. (2018) "Intergenerational transmission of trauma effects: Putative role of epigenetic mechanisms," World Psychiatry, 17(3), pp. 243–257. Available at: https://doi.org/10.1002/wps.20568.