CHICAGO/LONDON — Variations in a gene helped
shield adults who had endured child abuse from becoming
depressed as adults, US 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 non-familial 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. – Reuters
