Being bullied at school may leave a lifetime of emotional suffering for some children. Researchers say that even social environment can change the structure surrounding a gene that's associated with regulating the mood. A person with such changes in the genetic structure may have many mental health complications later in life.

"Many people think that our genes are immutable; however this study suggests that environment, even the social environment, can affect their functioning. This is particularly the case for victimization experiences in childhood, which change not only our stress response but also the functioning of genes involved in mood regulation," said Isabelle Ouellet-Morin, lead author of the study, from the Centre for Studies on Human Stress (CSHS) at the Hôpital Louis-H. Lafontaine.

Ouellet-Morin's earlier study found that children who were bullied secreted less cortisol (a stress hormone), but had problems with interacting with people and managing anger.

The current research found that two years before the children show a drop in cortisol secretion, a change occurs in the structure surrounding gene (SERT) that is associated with serotonin, a neurotransmitter that regulates mood and depression.

The study involved 28 pairs of identical twins who were at age 10 at the start of the study. Among the twins, one of them was bullied at school while the other wasn't.

"Since they were identical twins living in the same conditions, changes in the chemical structure surrounding the gene cannot be explained by genetics or family environment. Our results suggest that victimization experiences are the source of these changes," said Ouellet-Morin.

Ouellet-Morin says that future studies may try and find ways to prevent these psychological problems from occurring.