Sara Reardon in Nature:
Children from impoverished families are more prone to mental illness, and alterations in DNA structure could be to blame, according to a study published on 24 May in Molecular Psychiatry1. Poverty brings with it a number of different stressors, such as poor nutrition, increased prevalence of smoking and the general struggle of trying to get by. All of these can affect a child’s development, particularly in the brain, where the structure of areas involved in response to stress and decision-making have been linked to low socioeconomic status. Poor children are more prone to mental illnesses such as depression than their peers from wealthier families, but they are also more likely to have cognitive problems. Some of these differences are clearly visible in the brain structure and seem to appear at birth, which suggests that prenatal exposure to these stressors can be involved2.
From birth to adolescence
But neurodevelopment does not stop at birth. Neuroscientist Ahmad Hariri of Duke University in Durham, North Carolina, suspected that continual exposure to stressors might affect older children as well. He decided to test this idea by studying chemical tags known as methyl groups, which alter DNA structure to regulate how genes are expressed. There is some evidence that methylation patterns can be passed down through generations, but they are also altered by environmental factors, such as smoking. To test whether these mechanisms are involved in the increased likelihood of depression seen in impoverished children, Hariri and his colleagues zeroed in on a gene called SLC6A4, which encodes a protein that transports the brain-signalling molecule serotonin into neurons. The gene has long been known to be involved in depression, and the serotonin receptor is the target of many antidepressant drugs. Hariri and his colleagues collected blood samples from 183 Caucasian children aged 11–15, and tested the children for symptoms of depression. They also examined how the children responded to stress by scanning their brains to monitor activity when shown a picture of a frightened face. People who are highly sensitive to threats show more activity in the amygdala — the brain’s ‘fight or flight’ centre — when they see such an emotion.