Twins are a jackpot for research psychologists. In a field constantly seeking to unravel the effects of genetics, environment, and life experiences, they provide a naturally controlled experiment as paths subtly or dramatically diverge throughout adulthood.
Take Dennis and Douglas for example. In high school, the twins looked so much alike that their friends would tell them apart by the cars they drove, a Virginia study of twins told researchers. Most of their childhood experiences were shared, except that Denise endured attempted sexual abuse when she was 13 years old.
At age 18, Douglas married his high school girlfriend. He raised his three children and became deeply religious. Dennis had a number of short-lived relationships, was divorced twice, and each breakup led to days of despair. Dennis had a history of major depression by the time he was in his 50s, but his younger brother did not.
Why do twins who share many genetic and environmental influences experience mental illness differently as adults? On Wednesday, a team of researchers from the University of Iceland and Sweden's Karolinska Institutet reported new findings regarding the role played by trauma.
A study of 25,252 Swedish adult twins published in JAMA Psychiatry found that children had experienced one or more childhood incidents, including physical or emotional neglect or abuse, rape, sexual abuse, hate crimes, or witnessing domestic violence. It was found that those who reported these traumas were 2.4 times more likely to experience this type of trauma. Being diagnosed with a mental illness, as well as those who are not diagnosed with a mental illness.
If a person reported one or more of these experiences, the odds of being diagnosed with a mental illness jumped by 52 percent for each additional adverse experience. Of the participants who reported three or more adverse experiences, nearly a quarter had a psychiatric diagnosis of a depressive disorder, anxiety disorder, substance abuse disorder, or stress disorder.
To disentangle the effects of these traumas from genetic or environmental factors, researchers narrowed the pool to “discordant” pairs, in which only one twin reported being abused in childhood. there were. An analysis of 6,852 twins from these discordant pairs found that childhood maltreatment was still associated with adult mental illness, although not as strongly as the overall cohort.
“These findings suggest that there is a larger impact than I had expected; that is, even after controlling for common genetic and environmental factors very tightly, childhood adversity and We still observed an association with poor mental health in adults,” said PhD candidate Hilda Björk Danielsdóttir. University of Iceland and lead author of the study.
Twins who reported abuse were 1.2 times more likely to suffer from mental illness than unaffected twins in identical twin pairs, and 1.7 times more likely in dizygotic twin pairs. This effect was particularly pronounced among subjects who reported experiencing sexual abuse, rape, and physical neglect.
In an emailed response to questions, Danielsdottir said twins may have different childhood traumatic experiences for a variety of reasons. In 93 percent of cases in which individuals reported rape, the other twin had not been raped.
Domestic violence is “familial in nature” and is a common experience in more than half of cases, but twins may have different relationships with their parents, she said. For example, one twin may be more likely to conflict with a dysfunctional parent. Danielsdottir herself is an identical twin, and she said, “I can confirm that we have different relationships with our parents (both good).”
growing evidence
For decades, researchers have been accumulating evidence linking child abuse and maltreatment to later disease. A landmark 1998 study of 9,508 adults found direct correlations between childhood abuse and heart disease, cancer, lung disease, and depression, often associated with smoking and alcohol consumption. It was found that these behaviors are related to
“That brought everything into the light,” said Dr. Jeremy Wellef, a psychiatrist at Yale University School of Medicine who studies the effects of childhood adversity.
For decades, research has focused on biomedical models of mental illness, but this discovery moves toward investigating the influence of early childhood experiences, including social conditions such as racism, housing, and poverty. helped facilitate the transition.
The two lines of research have been combined in a study to map the effects of trauma on the brain. A 2022 report published in the journal “Molecular Psychiatry” in Nature points to specific changes in “stress-sensitive brain regions” in people who have been abused in childhood, and suggests that psychiatric diagnoses are associated with trauma. It recommended that a modifier be added to reflect the history of the country.
“Horrible events that happen to children and young people change the brain, physically change the brain, and in some ways cause mental illness,” Dr. Verev said. “In any case, the mental illness you may have developed may be more difficult to treat, worse, or even fundamentally different.”
Mark Bellis, professor of public health at Liverpool John Moores University in the UK, said by ruling out the role of genetic factors, the new findings show that childhood abuse leads to poorer mental health in adulthood. He said that this should help dispel remaining doubts. Involved in research.
The findings provide a rebuttal that it would be much cheaper for all of us if we invested in efforts to tackle child abuse and neglect now, rather than continuing to pay for widespread levels of harm. “This further strengthens the evidence that it cannot be done,” he added. The cause is downstream.
