Numerous scientific studies point to the fact that trauma experienced by older generations can be passed down to their offspring through epigenetic mechanisms.
Trauma. Image Credit: OneSideProFoto/Shutterstock.com
Introduction to epigenetics
The human genome is made up of deoxyribonucleic acid (DNA), which is the genetic code that contains a continuous sequence of the nucleotide bases adenine (A), cytosine (C), guanine (G), and thymine (T). Through a process known as transcription, these genetic sequences are converted into messenger ribonucleic acid (mRNA) sequence.
After transcription has occurred, mRNA sequences are then used to build amino acids which are the basic building blocks of proteins and peptides through a process known as translation. During the post-translational period, further modifications to the protein can occur to alter how it functions.
Epigenetic modifications, for example, can arise during this period to regulate the function of the genes that encode for proteins. Epigenetics is defined as the study of the functionally stable and inherited changes on genetic phenotypes that occur without any alterations in the actual genetic sequences.
DNA methylation, which is the attachment of methyl (CH4) groups to the DNA molecule, is the most widely studied epigenetic mechanism. Typically, DNA methylation affects the promoter gene, ultimately causing this gene to be repressed during transcription.
Epigenetics in psychiatry
Several studies have found a correlation to exist between DNA methylation of genes and certain psychiatric conditions. For example, an association between DNA methylation and both depression and suicide has been confirmed. More specifically, the hypermethylation of the BDNF promoter or TrkB were found to have significant involvement in individuals who had committed suicide.
A group of researchers has also examined genome-wide blood DNA methylation profile changes and their influence on whether the test subjects experienced symptoms of post-traumatic stress disorder (PTSD). This study found that the subjects, all of whom were military veterans, who exhibited DNA methylation changes also developed PTSD symptoms.
Epigenetics and inherited trauma
Both in vitro and in vivo data point to the potential role that epigenetic modifications, particularly DNA methylation, have in mediating the ability of trauma to be passed from parents to their offspring. Since animal models of PTSD and trauma are limited in their ability to translate how these epigenetic modifications might occur in humans, several studies on individuals who have experienced traumatic events have been conducted.
Despite the fact that over 85% of Rwandans are Hutus, the Tutsi minority of the country maintained control of the country for several decades. After a plane carrying then-President Juvenal Habyarimana and Cybrien Nataryamira of Burundi, both of whom were Hutus, was shot down in 1994, Hutu extremists took the opportunity to initiate the Rwanda genocide. In just 100 days during this year, over 800,000 people in Rwanda were murdered.
In 2011, it was estimated that over 20% of the Rwandan population met the criteria for PTSD as a result of their experience surviving the genocide. Twenty-five widows who were pregnant during the genocide, as well as twenty-five women who were also pregnant but living abroad, were included in a study looking to identify the transgenerational effect of PTSD on offspring.
This study found that the children born from mothers who lived in Rwanda during the genocide had significantly higher levels of both PTSD and depression as compared to those whose mothers lived abroad. Additionally, the children of Rwanda-based mothers were found to have higher methylation levels present at the exon 1F promoter of the glucocorticoid receptor NR3C1 at CpG3-CpG9.
Furthermore, the children of mothers who were exposed to trauma were found to have lower cortisol levels as compared to children who were born from non-exposed mothers. This latter finding is significant, as lower cortisol levels have been found to correlate to PTSD symptoms.
Between 1941 and 1945, Nazi Germany was responsible for the death of almost 6 million Jewish people during the Holocaust. A total of 32 Holocaust survivors and their 22 offspring, along with 8 control subjects and their 9 offspring, were recently studied to determine whether DNA methylation changes occurred on FKBP5, which is a moderator of glucocorticoid activity.
To this end, methylation levels were found to be significantly higher at FKBP5 intron 7 in Holocaust survivors as compared to the control subjects, whereas the offspring of Holocaust survivors instead exhibited lower methylation levels at this same gene as compared to their older family members. This opposing effect seen on the FKBP5 intron 7 methylation levels is believed to be due to a biological accommodation by the genetics of the offspring; however, further work is needed to fully understand this phenomenon.
Despite the availability of data supporting a potential role by which trauma is inherited through epigenetic changes, this field of study is still in its infancy. In fact, several epigenetic researchers refute the plausibility of these claims, claiming that the evidence on which they are based are not strong enough to make these correlations.
Regardless of the criticism surrounding this topic, further studies must still be conducted to fully understand whether children can inherit the psychological effects of trauma from older generations.
- Youssef, N. A., Lockwood, L., Su, S., et al. (2018). The Effects of Trauma with or without PTSD, on the Transgenerational DNA Methylation Alterations in Human Offsprings. Brain Sciences 8(5). doi:10.3390/brainsci8050083.
- Jiang, S., Postovit, L., Cattaneo, A., et al. (2019). Epigenetic Modifications in Stress Response Genes Associated with Childhood Trauma. Frontiers in Psychiatry. doi:10.3389/fpsyt.2019.00808.
- Can We Really Inherit Trauma? [Online]. Available from: https://www.nytimes.com/2018/12/10/health/mind-epigenetics-genes.html.
- Rwanda genocide: 100 days of slaughter [Online]. Available from: https://www.bbc.com/news/world-africa-26875506.