Aggression in boys may start before birth

"If our results show that behavioral problems originate from as far back as pregnancy, it means that we can reduce violence through preventive intervention from as early as pregnancy," says Richard Tremblay. (Credit: Peter Dutton/Flickr)

Chronic aggressive behavior exhibited by some boys from disadvantaged families may be due to epigenetic changes during pregnancy and early childhood.

A new study shows that men who displayed chronic aggressive behavior during childhood and adolescence have lower blood levels of four biomarkers of inflammation than in men who exhibited average levels of aggressive behavior in their youth, from 6 to 15 years of age.


“This means that using four specific biomarkers of inflammation, called cytokines, we were able to distinguish men with chronic physical aggression histories from those without,” says Richard Tremblay, professor emeritus at the University of Montreal.

In a second study, in the same men with aggressive pasts, the DNA encoding the cytokines showed methylation patterns different from those of the comparison group.

“Methylation is an epigenetic modification—hence reversible—of DNA, in relation to parental imprinting. It plays a role in regulating gene expression,”says Moshe Szyf, a professor at McGill University.

“The pre- and postnatal environment could cause these differences in biomarkers associated with chronic aggression,” Szyf says.

Various studies conducted with animals show that hostile environments during pregnancy and early childhood have an impact on gene methylation and gene programming leading to problems with brain development, particularly in regard to the control of aggressive behavior.

Begins with mom?

Previous work suggests that men with aggressive pasts have one thing in common: the characteristics of their mothers.

“They are usually young mothers at the birth of their first child, with low education, often suffering from mental health problems, and with substance use problems,” Tremblay says.

The significant difficulties these mothers experienced during pregnancy and the early childhood of their child may have an impact on the expression of genes related to brain development, the immune system, and many other biological systems critical for the development of their child.

For the two studies, published in PLOS ONE, researchers collected blood from 32 participants who took part in either of two longitudinal studies that began nearly 30 years ago. The first study followed young Quebecers from disadvantaged backgrounds, while the second involved a representative sample of children who were in kindergarten in Quebec in 1986-87.

It is important to note that in disadvantaged families, the rate of boys with chronic aggressive behavior represents about 4 percent of the population. This greatly restricts the selection of potential participants.

Disorganized lifestyles

“Once they are adults, they are difficult to find because they have disorganized lifestyles,” Tremblay says. “We are studying the impact of the socioeconomic environment on the third generation, now that these children are grown up and have children.”

While no study has yet been published on the subject, he anticipates “significant intergenerational ties, since we observed an association between parental criminality of the first generation and the behavior of their children.”

Nevertheless, Tremblay, who has conducted his work for decades with a prevention perspective, is optimistic.

“If our results show that behavioral problems originate from as far back as pregnancy, it means that we can reduce violence through preventive intervention from as early as pregnancy. We have already shown that support given to families of aggressive boys in kindergarten prevents school dropout and crime in adulthood.”

Source: McGill University