What’s New in Psychology?

Small Differences in a Mother’s Behavior Could Affect Later Stress Responses

Jim Windell

           We are all well aware of the importance of early development. And we basically know that the behavior of the primary caregiver will play a role in a child’s early – and perhaps later – development. But a new study links neutral maternal behavior toward infants with an epigenetic change in children related to stress response. 

           In case you’re not familiar with the term “epigenetic change,” the epigenome is a number of chemical compounds that can tell the genome what to do. The human genome is the complete assembly of DNA, some three billion base pairs, that makes each individual unique. DNA holds the instructions for building the proteins that carry out a variety of functions in a cell. The epigenome is made up of chemical compounds and proteins that can attach to DNA and direct the genes. They can turn genes on or off, thus, controlling the production of proteins in particular cells.

           In this new study that comes from the UK, researchers found that neutral or awkward behavior of mothers with their babies at 12 months correlated with an epigenetic change called methylation. Methylation is a chemical modification of DNA and other molecules that may be retained as cells divide to make more cells. When found in DNA, methylation can alter gene expression. In this process, chemical tags called methyl groups attach to a particular location within DNA where they turn a gene on or off, thereby regulating the production of proteins that the gene encodes.

            For this study, Elizabeth Holdsworth, a Washington State University biological anthropologist and lead author of the study published recently in the American Journal of Human Biology, and her co-authors analyzed a subsample of 114 mother-infant pairs from the Avon Longitudinal Study of Parents and Children, a project that tracks a cohort of children born in 1991 and 1992 in Avon, UK. 

           The researchers first analyzed data from an observational study of the mothers sharing a picture book with their children at 12 months. In this observation, mother’s interactions were coded on warmth. The study focused on mothers because they are often infants’ primary caregivers. The vast majority of the women in this sample were white, college-educated and from middle-income households. The range of warmth they displayed only varied slightly with the “coldest” behavior classified as awkward or neutral, but this is exactly what the researchers hoped to test: that if even small differences in social interaction could be linked to an epigenetic change.  

           The observed behavior was then compared against data from an epigenetic analysis of the children’s blood samples taken at age seven. The researchers found that the mothers showing awkward or neutral behavior toward their infant correlated with a small increase of methylation on the NR3C1 gene. This gene encodes a receptor involved in the regulation of the HPA axis – the interaction between the body’s hypothalamus, pituitary and adrenal glands. This axis plays a role in stress response, including production of the body’s primary “stress” hormone, cortisol.

           According to Holdsworth, “There is evidence of a relationship between the quality of maternal-infant interaction and methylation of this gene though these are small effects in response to a relatively small variation in interaction.”

           Other studies have connected extreme stress in early life, like neglect and abuse, to more dramatic methylation on this particular gene in adults. However, Holdsworth emphasized that the small difference indicated by this study may be an indication of normal human variation and it’s hard to determine if there are any long-term effects. 

           Researchers, like Holdsworth, are working to uncover how these changes happen, particularly during infancy when the body is developing rapidly – as well as what they might mean. “Within developmental biology, we know humans grow to fit the environment that they’re in, which contributes to normal human biological variation. It’s not necessarily good or bad,” Holdsworth said.  

           To read the original article, find it with this reference:

Holdsworth, E. A., Schell, L. M., & Appleton, A. A. (2023). Maternal–infant interaction quality is associated with child NR3C1 CpG site methylation at 7 years of age. American Journal of Human Biology, e23876.