What is the true cost of poverty? For kids in the United States, growing up poor can spell long-term economic troubles. One 2008 study showed that children who grow up in poverty make about 39 percent less than the median and reduce gross domestic product by 1.5 percent each year. And an increasing body of evidence shows that kids who grow up poor are prone to behavioral and educational problems. But there’s another cost: New research shows that poverty is linked to actual changes in a child’s DNA structure that are associated with depression.

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The study, which was published in the journal Molecular Psychiatry, followed 183 adolescents over the course of three years. After sampling their blood and testing them for depression symptoms, researchers showed them pictures of fearful faces while scanning their brain activity. Prior research shows that the amygdala—the brain center mainly associated with emotional reactions—of children prone to anxiety and depression have exaggerated, “fight-or-flight”-style responses to scared faces.

The research team repeated these tests over the course of three years, comparing each child’s results and looking at how the SLC6A4 gene—which is associated with serotonin production—changed over time.

During the course of the study, poor children had greater methylation of SLC6A4—a modification that suppresses how the gene functions. Poor participants’ brains also had more active amygdalae.

Overall, the results linked lower socioeconomic status to this change in the DNA structure, which is associated with changes in how the amygdala responded to perceived threats. For kids with an existing family history of depression, amygdala activity seemed to activate future depression—a pathway that might explain why kids who are exposed to the constant stress of poverty are more likely to develop mental health problems later on.

It’s not the first time DNA has been linked to poverty—in 2014, for example, scientists found that growing up in poverty and stress shortens DNA sequences. But the discovery of this link between DNA changes and subsequent depression in kids is noteworthy. As behavioral geneticist Robert Philipbert tells Nature’s Sara Reardon, the study suggests that changing a kid’s environment can change their neurodevelopment.

Next, writes Susan Scutti for Medical Daily, the team plans to see if there are other markers of genetic changes linked to poverty that can help predict depression. Perhaps continued research can fuel the fight to raise the one in three U.S. kids growing up below the poverty line into a higher socioeconomic bracket.