* Text Courtesy IANS

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(IANS) Bullying by peers at school may bring on mental health problems for children later by altering the expression of a gene involved in regulating mood.

"Many people think that our genes are immutable. However this study suggests that social environment can affect their functioning," said Isabelle Ouellet-Morin, professor at the University of Montreal and Centre for Studies on Human Stress (CSHS) at the Hopital Louis-H. Lafontaine.

"This is particularly the case for victimisation experiences in childhood, which change not only our stress response but also the functioning of genes involved in mood regulation," adds Ouellet-Morin, who led the study, the journal Psychological Medicine reports.

A previous study by Ouellet-Morin, conducted at the Institute of Psychiatry in London, UK, showed that bullied children secrete less cortisol -- the stress hormone -- but had more problems with social interaction and aggressive behaviour.

The study indicates that the reduction of cortisol, which occurs around the age of 12, is preceded two years earlier by a change in the structure surrounding a gene (SERT) that regulates serotonin, a neurotransmitter involved in mood regulation and depression, according to a Montreal statement.