A study published in Molecular Psychiatry in May, “Poverty linked to epigenetic changes and mental illness“, reports that children who grew up in poverty are more likely to develop depression rather than those who grew up in wealthier environments.
Stressors and Trauma of Poverty
Environmental stressors during development can change the structure and function of the brain as well as the expression of one’s genes. Impoverished children experience environmental and emotional stressors including lack of nutrition, exposure to smoking, parental neglect, and constant feelings of struggle and worry. Alterations in DNA or brain structure of children are often visible at birth, implying that they were passed on from parents. These modifications to DNA are due to the addition of methyl groups that change gene expression and function. In this case, methyl groups are added to the proximal promoter of the serotonin transporter gene, inhibiting transcription and leading to increased risks for mental illnesses such as depression.
SLC6A4 and Depression
A specific gene called SLC6A4 encodes proteins that transport serotonin to neurons and is associated with depression. According to the study, lower socioeconomic status during adolescence is associated with increased methylation of the SLC6A4 gene.
Researchers used behavioral data and neuroimaging from 132 adolescents over three waves, with 2 years between the first and second waves and 1 year between the second and third waves. The researchers tested for changes in SLC6A4 methylation, amygdala reactivity, and depressive symptoms at each wave. On average, adolescents with positive family histories of depression were of lower socioeconomic status, and lower socioeconomic status predicted greater increases in SLC6A4 methylation between waves. These adolescents had more methylation near the SLC6A4 gene in the amygdala (the area of the brain associated with emotion), and were more likely to become depressed themselves.
In addition, adolescents at higher risk for depression had increased reactivity in the amygdala between waves 1 and 2 when shown fearful faces (threat-related reactivity), predicted by the increased methylation of SLC6A4. In those with positive family histories of depression, increases in amygdala reactivity between waves 1 and 2 predicted more depressive symptoms between waves 2 and 3.
Unlike studies in the past that have focused on high levels of stress from single traumatic experiences, this study is based on lower levels of chronic stress. Evidently, there is an epigenetic cause of depression among those who grew up in poverty and developed while experiencing constant stressors. Adolescents of lower socioeconomic status often are exposed to smoking and poor nutrition as well as different types of familial conflict, all of which may affect DNA methylation in development.
Researchers hope to narrow the direct environmental cause of increased methylation in those of low socioeconomic status. Physical and emotional stressors from the environment have the ability to alter specific genes like SLC6A4, leading to direct causes of illnesses such as depression. Researchers are also seeking preventative techniques such as mindfulness to decrease threat-based amygdala activity in an effort to prevent depressive symptoms from occurring.