Twins are a bonanza for research psychologists. In a field that constantly seeks to tease out the impact of genetics, environment and life experiences, they provide a naturally controlled experiment where their paths diverge, either subtly or not. suddenly, during adulthood.
Take Dennis and Douglas. In high school, they were so similar that their friends could tell them apart based on the car they drove. told the researchers in a study of twins in Virginia. Most of their childhood experiences are shared – except that Dennis endured a molestation when he was 13 years old.
At age 18, Douglas married his high school girlfriend. He raised three children and became deeply religious. Dennis experienced short-lived relationships and was divorced twice, falling into a state of despair after each breakup. At age 50, Dennis had a history of severe depression, but his brother did not.
Why do twins, who have multiple genetic and environmental inputs, differ in their experiences of mental illness as adults? On Wednesday, a team of researchers from the University of Iceland and the Karolinska Institute in Sweden reported new findings on the role of childhood trauma.
Their study of 25,252 adult twins in Sweden, published in JAMA Psychiatryfound that people who had experienced one or more childhood traumas – physical or mental neglect or abuse, rape, sexual abuse, hate crimes or witnessing violence family strength – are 2.4 times more likely to be diagnosed with a mental illness than those who do not have the illness.
If a person recounts one or more of these experiences, the odds of being diagnosed with a mental illness increase sharply, up to 52% for each additional adverse experience. Among participants who reported three or more adverse experiences, nearly a quarter had a psychiatric diagnosis of depressive disorder, anxiety disorder, substance abuse disorder, or stress disorder.
To separate the effects of these traumas from genetic or environmental factors, the researchers narrowed the group to “discordant” pairs, in which only one twin reported maltreatment childhood. An analysis of 6,852 twins from these discordant pairs found that childhood maltreatment was still associated with adult psychopathology, although not as strongly as in the entire cohort.
“These findings show a larger effect than I expected — that is, even after very strict controls for genetic factors and shared environment, we still observed an association between childhood adversity and poor mental health outcomes in adulthood.” University of Iceland and first author of the study.
A twin reporting maltreatment is 1.2 times more likely to have a mental illness than an unaffected twin in identical twins and 1.0 times more likely to have a mental illness. 7 times in fraternal twins. This effect is especially pronounced in subjects who have experienced sexual abuse, rape, and physical neglect.
Ms. Danielsdottir said in an email response to questions that twins can have different experiences of childhood trauma for a variety of reasons. In 93% of cases where one person reported being raped, the other person did not experience it at all.
Although domestic violence is “inherently familial” and a shared experience in more than half of cases, twins can have different dynamics with their parents, she said. they. For example, a pair of twins is more likely to have to deal with a dysfunctional parent. Ms Danielsdottir herself is an identical twin and said she “can confirm that we have different relationships with our parents (both good)”.
The evidence is growing
For decades, researchers have accumulated evidence linking childhood abuse and maltreatment with illness later in life. A landmark 1998 study of 9,508 adults found a direct correlation between childhood maltreatment and heart disease, cancer, lung disease and depression, often linked to behaviors such as smoking and alcohol use.
“That broke everything,” said Dr. Jeremy Weleff, a psychiatrist at Yale University School of Medicine who has studied the effects of childhood adversity.
For decades, research has focused on biomedical models of mental illness, but these findings have helped spur a shift in examining the impact of childhood experiences, including social conditions such as racism, housing and poverty.
Two lines of inquiry have merged in research mapping the effects of trauma on the brain. ONE 2022 report in Molecular Psychiatry, a Nature journal, showed specific changes in “stress-prone brain regions” in people who were abused as children and recommended that psychiatric diagnoses should added adjustment factors to reflect injury history.
“Terrible things that happen to children and adolescents change the brain, they change the brain physically and in some ways cause mental illness,” Dr. Weleff said. “Either way, the mental illness that may have developed will be more difficult to treat, or worse, or may even be fundamentally different.”
Mark Bellis, a professor of public health at Liverpool John Moores University in the UK, said that by ruling out a role for genetic factors, the new findings should help dispel any remaining doubts that Childhood maltreatment leads to worse mental health in adulthood. participate in research.
He added that the findings add to “increasingly irrefutable evidence that it would cost us a lot less if we invested in tackling” child abuse and neglect. children now, instead of “continuing to pay the price for the damage” they cause downstream.
