"Long before it's in the papers"
January 27, 2015


Could changes to your chromosomes make you aggressive?

Sept. 29, 2013
Courtesy of Université de Montréal
and World Science staff

Chron­ic ag­gres­sion in some boys from poor­er fam­i­lies may stem from “epi­ge­net­ic” changes—changes to the chro­mo­somes, in turn af­fect­ing the genes, re­search sug­gests.

These changes would oc­cur dur­ing preg­nan­cy and early child­hood, and may stem from sub­stance use or ment­al health prob­lems in the moth­ers’ lives, ac­cord­ing to two stud­ies, led by Rich­ard E. Trem­blay of the Uni­vers­ity of Mont­real and Mo­she Szyf of McGill Uni­vers­ity in Can­a­da.

A graph­ic showing how how ep­i­ge­net­ic changes work. A key step is DNA meth­yl­a­tion, in which a mol­e­cule called a me­thyl group at­taches it­self to the DNA and there­by ac­ti­vates or re­presses genes. The meth­yl­a­tion af­fects the way DNA is "wrapped up" around struc­tures called hi­s­tones, which look like yo-yos. This wrap­ping causes genes in the wrapped-up sec­tion of DNA to be re­pressed be­cause they're in­ac­ces­si­ble to oth­er cel­lu­lar mech­a­nisms. (Im­age cour­te­sy U.S. Nat'l Can­cer In­sti­tute)

Trem­blay’s team found that among men who showed chron­ic ag­gres­sion in child­hood and ad­o­les­cence, blood lev­els of four chem­i­cals in­di­cat­ing in­flamma­t­ion were low­er than in men who showed av­er­age lev­els of ag­gres­sion dur­ing that time, from 6 to 15 years of age.

By test­ing for these four molecules, called cy­tokines, “we were able to dis­tin­guish men with chron­ic phys­i­cal ag­gres­sion his­to­ries from those with­out,” said Trem­blay, a re­searcher spe­cial­iz­ing in de­vel­op­men­tal psy­chol­o­gy. 

Szyf’s study found that in the same men with ag­gres­sive pasts, the DNA code for pro­duc­ing these cy­tokines had un­der­gone “epi­ge­net­ic” changes. These oc­cur when mo­le­cules known as me­thyl groups be­come at­tached to spe­cif­ic ar­eas of the DNA and change the lev­els of ac­ti­vity there.

“Methyla­t­ion is an ep­i­ge­net­ic modifica­t­ion—hence re­versible—of DNA,” and is al­so a way in which bi­o­log­i­cal ac­ti­vity in the par­ent or en­vi­ron­men­tal fac­tors can make an im­print in off­spring, said Szyf. “The pre- and post­na­tal en­vi­ronment could cause these dif­fer­ences.”

Stud­ies in an­i­mals show that hos­tile en­vi­ronments dur­ing preg­nan­cy and early child­hood af­fect me­thyla­t­ion, lead­ing to prob­lems with brain de­vel­op­ment, he added.

Pre­vi­ous work by Trem­blay’s team sug­gests men with ag­gres­sive pasts have one thing in com­mon: their moth­ers’ char­ac­ter­is­tics. “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 ex­plained. The trou­bles these moth­ers ex­pe­ri­ence may have an im­pact on the ac­ti­vity of genes re­lat­ed to brain de­vel­op­ment, the im­mune sys­tem, and many oth­er bi­o­log­i­cal sys­tems in the child, he said.

The find­ings were pub­lished in two pa­pers published July 26 and Aug. 19 in the jour­nal Pub­lic Li­brary of Sci­ence One. Szyf and Trem­blay su­per­vised the first au­thor of both pa­pers, Na­dine Pro­ven­çal.

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Chronic aggression in some boys from disadvantaged families may be due to “epigenetic” changes—changes to the chromosomes, in turn affecting the genes, research suggests. These changes would occur during pregnancy and early childhood, and may stem from substance use or other problems in the mothers’ lives, according to two studies, led by Richard E. Tremblay of the University of Montreal and Moshe Szyf of McGill University in Canada. Tremblay’s team found that among men who showed chronic aggression in childhood and adolescence, blood levels of four chemicals indicating inflammation were lower than in men who showed average levels of aggression during that time, from 6 to 15 years of age. By testing for these four molecules, called cytokines, “we were able to distinguish men with chronic physical aggression histories from those without,” said Tremblay, a researcher specializing in developmental psychology. Szyf’s study found that in the same men with aggressive pasts, that the DNA code for the production of these cytokines had undergone “epigenetic” changes. Epigenetic changes occur when molecules known as methyl groups become attached to specific areas of the DNA and change the levels of activity there. “Methylation is an epigenetic modification—hence reversible—of DNA,” and is also a way in which biological activity in the parent or environmental factors can make an imprint in offspring, said Szyf. “The pre- and postnatal environment could cause these differences.” Studies in animals show that hostile environments during pregnancy and early childhood affect methylation, leading to problems with brain development, he added. Previous work by Tremblay’s team suggests men with aggressive pasts have one thing in common: their mothers’ characteristics. “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 explained. The troubles these mothers experience may have an impact on the activity of genes related to brain development, the immune system, and many other biological systems in the child, he said. The findings were published in two papers in the journal Public Library of Science One. Szyf and Tremblay supervised the first author of both papers, Nadine Provençal.