Quote: Emerging science suggests that the effects of trauma—from war and genocide to abuse and environmental factors—could be genetically passed down from one generation to another.
 
Epigenetics is the study of how genes are turned off and on. The molecular process, known as gene expression, boosts the activity of some genes and quiets others by adding and removing chemical tags—called methyl groups—to genes. Multiple research studies have suggested that this may be a mechanism through which a parent’s trauma could be imprinted in the genes of offspring, and the epigenetic effects could be multi-generational.
 
The field "touches on all the questions that humanity has asked since it was walking on this planet," says Moshe Szyf, a professor of pharmacology at McGill University. "How much of our destiny is predetermined? How much of it do we control?"              
                                                                      
For some people, the concept that we can carry a legacy of trauma makes sense because it validates their sense that they are more than the sum of their experiences.
 
“If you feel you have been affected by a very traumatic, difficult, life-altering experience that your mother or father has had, there’s something to that,” says Rachel Yehuda, professor of psychiatry and neuroscience of trauma at Mount Sinai in New York. Her research points to a small epigenetic “signal” that a life-altering experience “doesn’t just die with you,” she says. “It has a life of its own afterwards in some form.”

Quote: 
Yehuda uncovered an epigenetic mark in Holocaust survivors and their offspring, a group at greater risk for mental health challenges. She assessed 32 survivors and their adult children in 2015, examining the FKBP5 gene—which has been linked to anxiety and other mental health concerns.
                                         
By extracting DNA from blood samples, the team identified epigenetic changes in the same region of the gene in the survivors and their children; but those alterations were not present in the DNA of a small group of Jewish parents and their offspring who lived outside of Europe and didn’t experience the Holocaust.
 
In a subsequent study published in 2020, Yehuda examined a larger cohort of subjects, looking at variables such as the sex and age of the parent during the Holocaust. She examined DNA methylation, one of the methods the epigenome uses to activate or quiet genes. DNA methylation generally adds a chemical mark to DNA; demethylation removes it.

Yehuda found that there were lower levels of DNA methylation in the FKBP5 gene in children whose mothers survived the Holocaust than in Jewish control subjects whose parents didn’t experience the Holocaust. Some studies have linked reduced DNA methylation in the FKBP5 gene to increased risk of disorders in adults such as PTSD. The results suggested that a mother’s trauma—even if it occurred during childhood—might lead to epigenetic changes within the DNA in her eggs and thus impact the mental health of her children.

Quote: 
A 2019 study with male Vietnam war veterans from Australia provides additional clues about how trauma transcends generations.
 
Researchers searched for methylation differences in the DNA encapsulated in the sperm of veterans suffering from PTSD and compared it to DNA of those without the condition. Ten regions of DNA showed different methylation patterns in PTSD veterans compared to non-PTSD veterans. The changes were present in nine different associated with psychiatric disorders such as PTSD. 
 
The methylation patterns in the vets with PTSD were linked with mental health conditions diagnosed in the veterans' children, according to the study. The findings identified a unique pattern of DNA changes which could be inherited, “especially those that are associated with the stress response,” says Divya Mehta, senior research fellow at Queensland University of Technology in Australia.