A new study provides the first scientific hint that living in big cities, experiencing physical or sexual abuse, migration, cannabis consumption, or problematic alcohol use as a child or teen leads to a higher risk of becoming a violently aggressive adult.
According to researchers, the study shows that growing up in extreme societal conditions can alter gene expression, the process known as epigenetics — changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.
The 32 researchers, led by Dr. Hannelore Ehrenreich of the Max Planck Institute of Experimental Medicine in Germany, found that children and adolescents who grow up with one or more of these environmental risk factors are likely to resort to violence, aggression and crime as adults, regardless of an underlying mental illness.
In a previous study, the researchers discovered that schizophrenia could develop about 10 years earlier in genetically predisposed people who grow up in high-risk conditions, such as suffering childhood maltreatment, sexual abuse, or head trauma.
The new study shows that the same high-risk conditions led to a five times’ greater likelihood of a person being hospitalized in forensic units because of violent behavior.
For this study, the researchers analyzed data from more than 1,500 people living with schizophrenia, accessed through the Göttingen Research Association for Schizophrenia (GRAS), as well as more than 550 members of Spain’s general population.
The researchers noted that they factored in aspects, such as whether the person grew up in an at-risk area, if he or she was living in a big city or had migrated, experienced forms of physical or sexual abuse, used cannabis, or engaged in problematic alcohol consumption before the age of 18 years.
The researchers then evaluated whether study participants had been convicted of violent crimes such as sexual assault, manslaughter, battery or murder.
The study found that people who had experienced at least one of the high-risk factors had a marginally higher chance of becoming violently aggressive. With every additional risk factor, this chance increased step-wise, in a stair pattern.
When all high-risk factors were considered together, a person with high risk load — three or more of these risk factors — was 10 times more likely to become violently aggressive.
“Our data support the concept of a disease-independent development of violent aggression in people exposed to multiple pre-adult environmental risk factors,” Ehrenreich said.
“In all cohorts, accumulation of pre-adult environmental hits was highly significantly associated with lifetime conviction for violent acts or high psychopathy and aggression-hostility scores as proxies of violent aggression and rule-breaking. Strikingly, we note that the composition of risk factors is interchangeable.”
The researchers subsequently carried out comprehensive epigenetic analyses of the blood samples of a subgroup of 142 people.
Higher levels of histone-deacetylase1 (HDAC1) mRNA were found in the samples of 33 men with a high-risk profile. HDAC1 is an “umbrella mediator” of epigenetic processes and changes that can be influenced by environmental factors, researchers explain.
“This is a first small hint of epigenetic alterations in our high-risk subjects,” Ehrenreich said.
“The results of this study should motivate socio-political actions, aiming at identifying individuals-at-risk and improving precautionary measures,” she said. “Risk factors, interchangeable in their long-term consequences, like urbanicity, migration and substance abuse, should be increasingly considered through more intensive research into primary prevention.”
The study was published in the journal Molecular Psychiatry, which is published by Springer Nature.