CHICAGO/LONDON (Reuters) - Variations in a gene helped shield adults who had endured child abuse from becoming depressed as adults, U.S. researchers said on Monday in a study that helps explain how nature and nurture give rise to mental illness.
And a British team has found that pregnant women who have a major emotional loss in the early months of pregnancy give birth to babies with a higher risk of schizophrenia.
The studies, published in the Archives of General Psychiatry, add to a growing understanding of how genetics and environmental distress sometimes act together to produce mental illness.
“It is not a question of genes versus environment. It is a question of how genes interact with whatever the environmental factors might be. And that is probably true of all of the disorders that we call mental illness,” said Dr. Thomas Insel, director of the National Institutes of Mental Health.
“There is going to be a genetic factor that gives you the risk. And it all depends on what happens in a person’s lifetime,” Insel said in a telephone interview.
In the depression study, Dr. Kerry Ressler of Emory University in Atlanta found that some variations in a gene that regulates the stress hormone corticotropin-releasing hormone, or CRH, could protect those who had been abused as children.
Ressler and colleagues took DNA samples from 422 adults, most of whom were poor and black, and found about a third of them had the genetic variations.
People in this group who also had a history of abuse had half the symptoms of moderate to severe depression as those who did not have the protective variations of this gene. The researchers repeated the study in 199 wealthier white adults and came up with similar results.
The study builds on other research linking genes and stressful events with depression. A 2003 study in New Zealand found that people with a short version of a gene that relays the chemical messenger serotonin were more prone to depression after losing a job or a loved one.
“What we think these days is there isn’t such a divide between nature and nurture,” Dr. Kathryn Abel of the Centre for Women’s Mental Health Research at Britain’s University of Manchester said in a telephone interview.
Abel’s schizophrenia study looked at 1.38 million babies born in Denmark between 1973 and 1995. Her team found the risk of schizophrenia was two-thirds greater among offspring whose mothers experienced the death of a relative during the first trimester.
The link disappeared after the first three months, however, perhaps because barriers are built up between mother and fetus later on that protect the unborn baby from stress hormones released by the mother.
Abel said it was possible the mother’s hormones may either have a direct impact on development of the fetus brain or affect it indirectly by altering the activity of certain genes.
Schizophrenia is known to run in some families, indicating a genetic component to the disease, yet 90 percent of cases are still classed as nonfamilial or sporadic.
The new study found the association between a family death and the risk of schizophrenia was only significant in this sporadic setting, where a child’s parents, grandparents or siblings had no history of mental illness.
Editing by Maggie Fox