Kids who frequently show anger could be struggling with mental health problems
What is the underlying cause when children are violent and aggressive? Norwegian researchers have now investigated this.
So far, researchers have not come up with a good answer to the cause of aggressive behaviour in children.
But now, a new study has looked at children with a diagnosis of conduct disorder, as well as children who have problems with violence and aggression, but who have not received this diagnosis.
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“I wanted to find out how aggression and violence develop through life. What is actually behind this kind of behaviour?” says Natalia Tesli.
She has led the study undertaken by the University of Oslo and the Norwegian Institute of Public Health.
How do aggression and violence arise?
In her doctoral thesis, Natalia Tesli studied MRI images of the brains of convicted violent offenders. She compared these with images of the brains of people who had not committed violence.
Tesli found a significant difference in the brains between the two groups. You can read more about that study here.
Now she wanted to look at how aggression develops throughout childhood.
She chose to study children and adolescents who had been diagnosed with conduct disorder, the diagnosis most often given when children and teens act out and are aggressive.
They must have exhibited socially unacceptable behaviour with a lot of aggression for at least six months to receive the diagnosis.
“This is a serious diagnosis that the healthcare system in Norway is quite cautious about giving,” says Tesli.
Genetic risk detected
The researchers found several surprising connections in the study led by Tesli.
They discovered that conduct disorder significantly aligns with the genetic risk present in children.
The children with
conduct disorder had an increased genetic risk of mental health problems that
usually start in childhood, such as ADHD and autism.
They also had an increased risk for diseases that occur in adulthood, like schizophrenia, bipolar disorder, and depression.
Linked two data sources
Those who are diagnosed with conduct disorder have had contact with child and adolescent psychiatric services, often due to aggressive behaviour and violence.
The Norwegian Patient Registry (NPR) records all diagnoses assigned by the specialist healthcare services.
But the researchers also wanted to find youth who exhibited less severe behavioural problems.
To find them, they used data from the Norwegian Mother, Father and Child Cohort Study (MoBa). About 100,000 children are included in this study.
Parents asked about aggression
Parents in the MoBa study completed a questionnaire when their children were five and eight years old.
Parents were asked whether their children had difficulties with outbursts of anger, or temper tantrums.
One of the questions was: Has your child had problems with violence against other children, at school or in kindergarten? They were also asked about violence against animals.
“These are behaviours that aren't necessarily picked up by the healthcare system,” Martin Steen Tesli says.
He is a specialist in psychiatry, a researcher at the Norwegian Institute of Public Health, and one of the co-authors of the study.
Multiple diagnoses
When the researchers linked the data from NPR and MoBa, they found that about 600 of the children could be said to have conduct disorder.
But many of these children – as many as 65 per cent – also had other mental health diagnoses.
"We see that some can have up to four different diagnoses, given at different times," Martin Steen Tesli says.
“We observed a particularly strong connection between having conduct disorder and ADHD. Over 14 per cent of the children with conduct disorder also had an ADHD diagnosis.”
Diagnosis detected in genes as well
Blood samples were taken from the parents who answered questions and from their children.
The blood samples were used to determine the genetic risk for mental health problems.
"Remarkably, we found the diagnoses and the parent's answers reflected in the children's genes," says Natalia Tesli.
Victims of bullying also found
The researchers posed two questions to find out more about the difference between genetic and environmental factors:
- How much education do the parents have?
- Has the child been subjected to bullying?
“Both are environmental factors that we know are very significant for children's development,” says Natalia Tesli.
The researchers then found yet another link to genetics.
Children who have been bullied also have greater genetic vulnerability to developing mental health problems later in life. These are disorders such as schizophrenia, bipolar disorder, and depression.
The effect was even greater if the parents of bullied children also had a lower level of education.
The researchers point out that it is important to bear in mind that our behaviour is always a result of both our genes and the environment we grow up in.
An expected link
Pål Zeiner is a specialist in child and adolescent psychiatry.
“We know quite a bit about the potential causes behind serious conduct disorders in children and adolescents," he says.
“Learning difficulties, language difficulties, ADHD, parental mental health issues, poor or neglectful child rearing, limited financial resources, and association with other youths with similar difficulties – all of these could substantially heighten the risk of developing conduct disorders.”
The research also indicates a considerable hereditary aspect to ADHD and autism.
“Genetic predisposition plays a role in the development of mental health problems. When people with a genetic predisposition live in environments that are not good, the sum of genetic and environmental factors can lead to the development of mental health problems," Zeiner says.
Critical of participant selection
However, Zeiner is critical of whether the study sample is representative of children with behavioural disorders. Only 41 per cent of the people asked to participate in the MoBa survey agreed to participate, and a considerable number dropped out by the time the children reached school age.
“The remaining participants are less likely to exhibit the risk factors associated with serious conduct disorders compared to the general population, such as low education attainment, low income, and being a single parent,” Zeiner points out.
The Norwegian Patient Registry data, derived from the specialist health service, represents a very small number of diagnosed cases of serious conduct disorder, casting doubt on whether they can represent all children with conduct disorders accurately, he suggests.
"Unfortunately, this makes the study somewhat weaker," he believes.
Confident in the results
“It's important to acknowledge that the MoBa sample has its limitations, including dropout and representativeness issues,” believes Natalia Tesli.
At the same time, she points out that this data set ranks among the world’s largest in terms of genetic data in children and adolescents.
“By looking at both diagnoses and traits associated with behavioural problems, we have approached this with two different methodologies. We can therefore be all the more confident in our results,” she says.
Reference:
Tesli et al. Conduct disorder - a comprehensive exploration of comorbidity patterns, genetic and environmental risk factors, Psychiatry Research, vol. 331, 2024. DOI: 10.1016/j.psychres.2023.115628
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Translated by Ingrid P. Nuse
Read the Norwegian version of this article at forskning.no
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