You might be familiar with the popular epigenetic study that suggests when mother rats lick their pups, they leave epigenetic marks on their babies’ DNA. This, in turn, helps them grow up to be calm adults. On the other hand, pups who receive very little licking, grooming, or nursing from their moms tend to grow up more anxious. It wasn’t their genes that dictated their stressed-out behavior, but their epigenome, which was shaped by the nurturing behavior of their mother early in life.
Could this hold true for humans? New research suggests it might. Well, perhaps not licking your babies, but holding them close and cuddling them might actually adjust epigenetic marks on their DNA. This could potentially influence their development as they get older.
Caretaking Adjusts Epigenetic Marks
According to a study in Development and Psychopathology, the amount of comforting and close contact between human caretakers and their babies can influence the amount of DNA methylation, an epigenetic mechanism connected to turning genes “off.” This adjustment to the children’s DNA may even persist several years later.
Methylation describes the addition of a methyl group, consisting of hydrogen and carbon atoms, to a specific area of DNA. These small molecules act to suppress gene expression, thus affecting how cells function.
Researchers at the University of British Columbia and BC Children’s Hospital Research Institute carried out a study involving 94 healthy children and their parents. The parents were asked to keep a record of their infant’s behavior – including fussing, crying, sleeping, or feeding – as well as how long their caregiving involved bodily contact. Then, when the babies grew to four and a half years old, the scientists collected their DNA by swabbing the insides of their cheeks.
Overall, the children who were more distressed as infants and didn’t receive as much physical contact had a molecular profile in their cells that indicated underdevelopment for their age. The varying levels of DNA methylation between the low and high contact groups hinted that the infants who were not shown enough affection might be lagging behind biologically.
The precise impact that childhood development has on adult health still has yet to be understood, but these results bring to light the ways in which the simple act of a parent’s touch has deep and potentially long-term consequences on gene expression. In a similar supporting study, investigators found that a mother’s behavior can “buffer” her child against the epigenetic effects of maternal depression and lack of contact.
In the current study, the researchers initially assessed four candidate genes they believed might have been differentially methylated – the glucocorticoid receptor gene (NR3C1), μ-opioid receptor M1 (OPRM1), oxytocin receptor (OXTR), and brain-derived neurotrophic factor (BDNF). While some of these genes are related to the neurobiology of social bonds and postnatal plasticity, none actually showed any association between methylation and early postnatal contact.
However, when the team expanded their view and looked across the entire genome, they found significant differences in methylation levels in other areas. They pinpointed consistent differences in methylation between children who received a lot of contact versus those who received little contact to five specific DNA sites. Of these five sites, two of them were located within genes related to the immune system and metabolism. Still, the downstream influence of these epigenetic differences on child development and health later in life remain unknown.
Epigenetic Age and Health
The group also measured “epigenetic age”, a concept that describes a consistent and predictable pattern of epigenetic marks that indicate biological age. The children who endured higher distress and did not receive as much contact had a lower epigenetic age than would be expected, considering their actual chronological age.
“In children, we think slower epigenetic aging might indicate an inability to thrive,” explained Michael Kobor, a Professor in the UBC Department of Medical Genetics who leads the Healthy Starts theme at BC Children’s Hospital Research Institute. Although further research is necessary, this discrepancy has previously been connected to poor health.
“We plan on following up to see whether the ‘biological immaturity’ we saw in these children carries broad implications for their health, especially their psychological development,” said Sarah Moore, lead author and postdoctoral fellow. “If further research confirms this initial finding, it will underscore the importance of providing physical contact, especially for distressed infants.”
Can We Reverse Marks on DNA?
Although it may sound like someone could be “epigenetically doomed” to bad health if their parents didn’t cuddle them enough, it’s interesting to consider other studies which suggest that epigenetic marks might be reversible. In a mouse study, for example, male mice were separated from their mothers repeatedly and, as a result, experienced early-life trauma which left distinct epigenetic marks behind on their DNA.
They even passed down these marks and the negative behavioral consequences that accompanied them. But, what’s more intriguing is that the mice’s behavior returned to normal when they lived in pleasant environmental conditions as they grew, and their offspring developed normally. The results demonstrate that negative effects of trauma might be corrected by an enriched environment with low stress in adult life.
If this is the case, it may be possible that children who are not shown enough affection as infants may be able to overcome any shortcomings if they’re given the proper care or exposed to a positive environment later on. As more research is carried out, we can begin to understand the far-reaching implications early life experiences have on our epigenome, our behavior, and our health.
Source: Moore, S.R., Kobor, M.S. et al. (2017). Epigenetic correlates of neonatal contact in humans. Development and Psychopathology, 29 (05): 1517.
Reference: The University of British Columbia. Holding infants – or not – can leave traces on their genes. UBC Faculty of Medicine. 27 Nov 2017. Web.