Scientists Are Discovering How Trauma Can Be Inherited

boy and his baby brother hide in the forest for months, sleeping in a hole dug underground. They must keep silent to avoid attracting the attention of the soldiers who have invaded their village, but one day, the baby starts crying and won’t stop. Terrified, the boy tries to hush his brother, holding him tight, but the baby cries and cries. The boy holds him tighter and tighter, desperately trying to make the baby stop crying to save both their lives, but his brother won’t stop. Until suddenly he does. The little body goes still, and the baby never makes another sound.

A generation later, the boy has a daughter. She is very successful, known nationwide for her work. But she suffers from asthma and has trouble breathing, especially when she becomes panicked. She is deeply fearful of abandonment and death. One might wonder: Was her father’s trauma passed on to her, manifesting itself in her physiological and psychological issues?

Scientists and therapists are now trying to understand how trauma — broadly defined as severe psychological distress following a terrible or life-threatening event — is shared across generations, whether the connection is biological or psychological, and how best to stop the legacy of pain.

here is mounting evidence that the offspring of trauma survivors — of genocide, war, slavery, famine and other traumatic situations — have a greater risk of depression, anxiety, post-traumatic stress disorder, alcoholism, metabolic disorders, and even premature death. But the big question is whether these traits are the result of overhearing their traumatized parents’ stories and adopting their behaviors, or whether the trauma actually changed the parents’ genomes in such a way that the consequences were passed down to their offspring.

“The conundrum with a phenomenon like this is how much of it is biological inheritance—that is, sperm and egg—versus social transmission of information, which is akin to Grandma sitting at the dinner table and talking to you about the atrocities that she and her family might have experienced,” says Brian Dias, an assistant professor of psychiatry and behavioral sciences at Emory University. “That’s really difficult to disentangle in the human condition… and I think there is compelling evidence on both sides of those mechanisms.”

One possible way these experiences could be transmitted is through epigenetic inheritance. Epigenetics generally refers to the effect the environment can have on gene expression — not if a gene is present in someone’s DNA, but whether it’s turned on or off. Epigenetic changes occur via molecules that can latch onto the genome, alterations to the way DNA is packaged inside a cell, or differences in RNA — the readout of a gene that instructs a cell to make a protein.

Scientists are exploring whether epigenetic alterations can be passed down to future generations by looking for these alterations to the genome inside sperm and egg cells.

“Epigenetic inheritance is the phenomenon by which life experiences or environmental factors — where we live, what we eat, anything that can influence us — can have effects which can be transmitted to our offspring, our children,” says Isabelle Mansuy, a professor in neuroepigenetics at the University of Zurich. “To be transmitted across multiple generations, the exposure has to be dramatic enough — long enough and serious enough — otherwise it may [contribute to] symptoms in the first generation,” but not subsequent ones.

Mansuy is researching transgenerational inheritance of trauma in mice. First, she exposes male mice to trauma by removing them from their mothers immediately after they’re born. After the mice grow up and have their own pups, she looks for differences in the behavior of their offspring. She finds that five generations of mice — the offspring, grand-offspring, great grand-offspring, and beyond — show cognitive and behavioral differences, acting more depressed and antisocial and taking more risks.

“RNA in sperm can be altered by direct exposure to trauma even in early life, and it can stay altered throughout life.”

Mansuy is also studying the mice’s sperm to see if there are any differences in the RNA, a marker of epigenetic changes. She discovered that the RNA in the sperm of the traumatized mice is significantly altered, but the RNA in the offspring’s sperm is normal. However, she sees other epigenetic changes in the second generation’s sperm, leading her to speculate that the initial changes in RNA in response to trauma may be transferred into other epigenetic changes in subsequent generations’ sperm.

“RNA in sperm can be altered by direct exposure to trauma even in early life, and it can stay altered throughout life,” Mansuy says. “But later, in downstream generations, it does not need to be altered for the symptoms to be expressed by the grand-offspring.”

There is some evidence of epigenetic changes in response to trauma in humans as well. Rachel Yehuda, a professor of psychiatry and neuroscience at the Mount Sinai School of Medicine, has spent many years studying Holocaust survivors and their children. She has discovered differences in both generations in levels of the hormones cortisol and glucocorticoid, which are linked to stress, inflammation, and metabolic function. In one study, Yehuda found epigenetic changes in both survivors and their children in a gene that affects glucocorticoid function and has been linked to PTSD and depression.

Not everyone is convinced epigenetic changes can be inherited, however, and many questions about the mechanisms remain. For example, it is unclear how the changes in sperm RNA result in differences in the brain and behavior. Also unknown is how trauma experienced physically or psychologically causes changes to sperm and egg cells.

“How do you get the message to the sperm in the first place from somewhere else in the body?” says John Greally, a genetics professor at Albert Einstein College of Medicine. “In theory, it is possible that you could have changes that are passed from some influence on the sperm to at least the zygote and the early embryo. How that would end up as some sort of mark that would influence one specific set of neurons in the brain later on in life, that’s very difficult to imagine.”

ess contentious than epigenetic inheritance is the notion that trauma changes people emotionally, and that can have an impact on their parenting styles. Clinical psychologist Yael Danieli has researched and treated survivors of horrific human traumas for more than 40 years and is the founder of the International Center for Multigenerational Legacies of Trauma. (One of her patient’s stories is described in the beginning of the article.) Danieli has identified several adaptational styles survivors adopt to cope with their traumatic experiences, which in turn affect the health and well-being of their children and grandchildren. She says that these coping styles and how the children adapt to them influence not only the child’s mental health but also their choice of career, friends, and spouse later in life.

“We have these adaptational styles that the survivor parents created, and it’s into this psychosocial-biological milieu that the children are born,” she says. “We’re not just talking about a bunch of symptoms or epigenetic PTSD. We’re talking about a world view. We’re talking about a way of being in the world.”

Survivors may have strict, authoritarian parenting styles and not express as much love or warmth toward their children. In other instances, there may be a role reversal where the adults rely on the children for support, which can be extremely stressful for the child. Brent Bezo, a doctoral student at Carleton College who spent time in Ukraine with survivors of the Holodomor genocide and their families, says these parenting styles can then be adopted by the children when they grow up and have their own offspring, passing the trauma on to the third generation.

“When children become parents, they often parent based on what their parents modeled… So the second generation grew up in this environment, and then when they had their own children, they often parented in the same way that their own parents did,” Bezo explains. “Then the third generation, the grandchildren, grew up with these strict controlling parents, in a similar environment as their own parents, even though the genocide had taken place decades and decades earlier. The impact is still passed down generation to generation.”

Regardless of how the trauma is inherited, the important thing is to stop the transmission to the next generation.

What’s more, given the extent of the trauma experienced during the genocide, affecting people at an individual, familial, community, and national level, Bezo says it’s no surprise that future generations would experience physical and mental health effects. For example, Ukrainians experience higher rates of alcohol abuse and suicide, as well as lower life expectancy.

“Subsequent generations are growing up in this environment with many, many risk factors in terms of altered family functioning, mistrust of others on a societal level, strict controlling parents, hostile parents, lack of warmth and nurturing, poverty, lower socioeconomic status, loss of language and culture that stems from those events in the early 1930s,” he says. “Any one of those could be considered a risk factor for poor mental or physical health.”

egardless of how the trauma is inherited, the important thing is to stop the transmission to the next generation. Danieli and Bezo both say one of the most important steps is to acknowledge and discuss the atrocities. Doing so allows the survivors to process their pain and helps the families understand and make sense of their parents’ and grandparents’ behaviors. Group sessions can be particularly beneficial for survivors to empathize and relate with others who went through the same experience.

Dias, the Emory scientist who researches epigenetic inheritance in mice, agrees that improving treatment is the big-picture goal. With this in mind, whether the trauma is passed down through biological inheritance or social transmission matters less than “trying to buffer the next generation,” he says. “I think we’re consumed with this idea of things being inherited, and passing down is passing down in some respects.”

Dana G Smith

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Dana G Smith

Senior Writer for Elemental @ Medium covering health, science, and the science of wellness | dsmith@medium.com

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