By Diane Nelson
Our genes can influence how we respond to stress. Science shows that some people are more genetically predisposed than others to develop depression and anxiety in response to stressful situations.
What’s more, researchers say that chronic exposure to stressful conditions—such as poverty, family discord, and poor nutrition—can alter the way genes behave in children and adolescents, making them more susceptible to depression, anxiety, and other negative effects of stress.
But mounting evidence from scientists with the UC Davis Department of Human Ecology suggests there is also an upside to the link between genetics and environmental exposure. In many cases, the same people who are most adversely affected by negative experiences also benefit the most from supportive and even benign environments.
“It’s not just that some individuals are more ‘vulnerable’ to adversity, but rather that some people are more developmentally malleable for better and for worse,” said Jay Belsky, professor of human development. “Many of the genes long thought to operate as a risk factor for problem behavior when things go poorly may also be an opportunity factor when children are exposed to interventions and when things go well.”
Belsky and his colleague, human development professor Johnna Swartz, are uncovering intriguing clues about the connection between genetics, stress, and opportunity that could change the way society views, treats, and prevents depression, anxiety, and other disorders.
Fight or flight
Swartz and others have discovered that measures of brain function, which are influenced by genetic variation, may predict later psychiatric conditions. Working with Professor Ahmad Hariri at Duke University, Swartz analyzed the brain scans of 340 college students while they were looking at images of angry or fearful faces. Swartz and colleagues measured activity in the students’ amygdala—the tiny emotion-processing center of the brain—to see how active it was in response to the threatening stimuli.
After the measurements were taken, the students answered questions assessing stress in their lives as well as symptoms of depression and anxiety. Students with more reactive amygdalae at the start of the study—more exaggerated “fight-or-flight” responses to the scared and angry faces—experienced more severe symptoms in response to later stressful situations in their lives.
“By identifying genetic markers that predict these patterns of brain function, we could potentially guide people at higher risk for depression and anxiety to seek preventative treatment before symptoms become chronic and disruptive in their lives,” Swartz said.
With further research, genetics could also help doctors identify the imbalance or pathway causing a patient’s disorder and more precisely treat the problem.
Both nature and nurture seem to play a role in how people process stressful experiences. New research from Swartz and Professor Douglas Williamson at Duke University links poverty to changes in gene expression.
Their study followed 183 children ages 11 to 15 over three years, testing them for symptoms of depression and scanning their brain activity in response to photos of fearful faces. During the course of the study, children from more disadvantaged families had greater methylation—a process that can change the way genes behave—of a gene that controls levels of serotonin, which can affect a person’s mood. Children with more methylation also had more active amygdalae, and this predicted greater increases in depression symptoms a year later.
“The small, daily challenges of scraping by can build up and affect children’s development,” Swartz said. “It shows that our biology is not set in stone, and environments can affect us as deeply as levels of markers on our DNA.”
The bright side of susceptibility
Collaborating with scientists across the globe, Belsky has spent years researching “differential susceptibility”—the concept that some children are more likely to suffer in bad settings and flourish in good ones due to their genetic makeup. He has looked at the effect of quality care at orphanages in Portugal, the link between prenatal stress and attention deficit hyperactivity disorder, and how peer relations influence hyperactivity and impulsivity, just to name a few areas of research. And he has found a genetic connection.
For example, some variations of the serotonin-transporter gene have been linked to depression. And variations of the dopamine-receptor gene have been linked to attention deficit hyperactivity disorder.
But that’s not all.
“Intriguingly, these supposed ‘risk’ genes also turn out to be associated with heightened sensitivity to environmental conditions,” Belsky said. “Children who carry either or both of them appear to be most adversely affected by negative experiences, and seem to benefit most from supportive ones.”
And children without them seem relatively immune to the effects of both supportive and unsupportive environments.
“Some people are more affected by their developmental experiences than others,” Belsky said. “I think of it more as diversity rather than damage. Genetics can inform our understanding of human development and help us find ways for all of us to thrive.”
Diane Nelson is a writer with the UC Davis College of Agricultural and Environmental Sciences.