The ghosts of your past trauma might be the methylation patterns on your DNA (amongst other things)
Content warning: mentions of famine, the Holocaust, and suicide
When researchers at McGill University analysed 41 brain samples from the Quebec Suicide Brain Bank, they found that those who had faced significant early-life trauma had significantly different epigenetic marks compared to those without trauma.
But what are epigenetic marks, other than one of the (potential) reasons behind your attachment issues? In the broadest sense, epigenetics refers to everything that changes the function of a gene without changing the DNA sequence. At a molecular level, epigenetic marks can be various changes ranging from methylation of bases to various histone modifications. These changes can be affected by the food you eat, the air you breathe, and the drugs you take. Epigenetics is a dynamic interplay between nature and nurture.
Research has indicated that epigenetic markings associated with stress and trauma are particularly prevalent in the neurons involved in the hypothalamic-pituitary-adrenal (HPA) axis. Studies have indicated that promoters of several genes involved in neuronal plasticity in the hippocampus were shown to be hypermethylated in people with early-life trauma. Further, the expression of a hippocampal glucocorticoid receptor (GR) that is responsible for activating the HPA axis was found to be reduced in people with a history of child abuse. The hypermethylation of GR promoters has also been associated with parental abuse which can lead to gene silencing and reduced expression. These results are not surprising because the HPA axis is involved in the stress response, and its dysregulation can lead to significant psychiatric and emotional problems as well as suicide.
Epigenetic changes in the context of trauma have garnered significant attention in recent years, not only because they can act as molecular signs of various disorders but also because of intergenerational trauma. Intergenerational trauma is the idea that the effects of adverse experiences that your parents faced can be passed down to you mostly through nongenomic—or epigenetic—ways. It is undoubtedly true that people can feel the effects of the misfortunes their parents might have faced. The real question is did they ‘inherit’ these effects via the parental germline, or did they develop them in response to happenings in their own lives? Can people genetically pass trauma down to their children? Does your DNA remember the trials your parents faced? Do the epigenetic marks reveal their tribulations? In the age of flat-earthers and anti-vaxxers, it is important to look at what the evidence says. And the evidence is…complicated.
The idea of intergenerational trauma came into being with Rakoff’s observations on how the children of Holocaust survivors often had intense psychiatric problems. Studies, albeit done with convenience samples of volunteers, also found a higher incidence of post-traumatic stress disorder (PTSD) and mood and anxiety disorders in adult offspring of Holocaust survivors. Additionally, offspring of Holocaust survivors tended to have HPA axis changes like lower cortisol levels, in accordance with other offspring who had parents exposed to trauma, such as offspring of war veterans or 9/11 survivors. These effects were distinct based on the parental source of the trauma. Before these seminal reports, behavioural transmission was the only theory that had been considered to play a direct role, but some space was made for epigenetic mechanisms as an explanation, particularly because of the variable phenotypes that it can cause.
A growing body of evidence points to another source of epigenetic changes—in-utero exposure to stress. There is some evidence using animal models that indicates that perturbations in the prenatal environment can affect the development of the HPA axis using epigenetic mechanisms. The importance of the uterine environment in establishing epigenetic effects on the offspring was also demonstrated in the studies of a cohort of women and their children and grandchildren from the Dutch Winter Hunger. This was the famine of 1944 to 1945 that resulted due to the Nazis disrupting food supplies to the Netherlands. Children of pregnant women who had been exposed to the famine not only had differential methylation patterns at various genomic loci but also poorer health. The phenotype of poorer health was also seen in grandchildren of the same lineages.
Nonetheless, none of the evidence discussed shows that epigenetic effects of trauma in humans are transmitted via the germ cell (egg and sperm cells), which is what would make the effect truly transgenerational. Studies in animal models have provided some evidence to give traction to the idea of epigenetic inheritance, but such findings are yet to be replicated in humans and as of now, intergenerational trauma might be a bit of a misnomer. However, it is a powerful concept that has resonated with various communities that have faced extraordinary hardships over multiple generations, and the incongruence of its name with precise scientific language does not take away from the validity of their experiences.
