Teenage stress is serious, according to a new study that found a link between adolescent stress and genetic changes that can lead to severe adult mental illness.

A new study published in the journal Science revealed that elevated levels of a stress hormone in adolescence were associated with genetic changes in adulthood that cause severe mental illness in those predisposed to it.

Scientists at Johns Hopkins University say that the latest findings could have implications in both the prevention and treatment of schizophrenia, severe depression, and other mental illnesses.

"We have discovered a mechanism for how environmental factors, such as stress hormones, can affect the brain's physiology and bring about mental illness," lead researcher Dr. Akira Sawa, a professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine, said in a statement.

"We've shown in mice that stress in adolescence can affect the expression of a gene that codes for a key neurotransmitter related to mental function and psychiatric illness," he said.

Sawa and his team found that while isolating healthy mice from other mice for three weeks during the equivalent of rodent adolescence had no effect on their behavior, separating mice known to have a genetic predisposition to characteristics of mental illness exhibited behaviors associated with mental illness like hyperactivity.

Researchers said mice predisposed to mental illness that were isolated also failed to swim when put in a pool, which researchers say is an indirect correlate of human depression.

Investigators found that when the isolated mice with genetic risk factors for mental illness were returned to group housing with other mice, they continued to exhibit these abnormal behaviors. Researchers said that the latest findings suggest that the effects of isolation last into adulthood.

Sawa explained that while genetic risk factors were required to cause behaviors associated with mental illness in mice, only by adding an external stressor (in this case excess cortisol related to social isolation) did the mice show dramatic behavioral changes.

Furthermore "mentally ill" mice not only had elevated levels of cortisol, but also significantly lower levels of the neurotransmitter dopamine in a specific region of their brains involved in higher brain function like emotional control and cognition.

Previous studies have found that changes in dopamine levels in the brains of patients with schizophrenia, depression and mood disorders.

To see if cortisol levels were influencing dopamine levels in the brain and adult behavioral patterns in abnormal mice, researchers gave the mice a chemical compound called RU486, a drug commonly known as the "abortion pill" which blocks cells from receiving cortisol.

RU486 has also been shown in past clinical trials to work in people with hard-to-treat psychotic depression.

Researchers said that abnormal mice given the drug were able to swim longer, were less hyper and had normalized dopamine levels.

Sawa and his team studied the gene tyrosine hydroxylase (Th) to understand how and why the mice got better.

The found that the addition of a methyl group to one of the gene's DNA letters limited the gene's ability to do its job, which is to create an enzyme that regulates dopamine levels. Researchers explained that dopamine levels are abnormally low when the Th gene isn't working properly.

Rather than making permanent genetic alterations by changing the actual letters of the DNA sequence, epigenetic alterations caused by stress add a chemical group like methyl that can affect the function of the DNA.

Sawa and his team said the latest findings highlights the need for better preventive care in teenagers who have mental illness in their families. Preventive measures could include efforts to protect them from social stressors, such as neglect or abuse.

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