Parents' Stress Leaves Mark on DNA of Children
Madison, Wisconsin - Parents who are stressed during their children's early years can leave an imprint on their sons' or daughters' genes - an imprint that lasts into adolescence and may affect how these genes are expressed later in life, according to a study by researchers at the University of Wisconsin and the University of British Columbia.
The study, published online today in the journal Child Development, focused on epigenetics - the expression of genes, as opposed to the underlying sequence of DNA. A central component of epigenetics is methylation, in which a chemical group attaches to parts of the DNA - a process that acts like a dimmer on gene function in response to social and physical environments.
Dr. Marilyn Essex, a professor of psychiatry at the UW School of Medicine and Public Health, has been conducting research on participants in the long-running Wisconsin Study of Families and Work. This ongoing project follows the health and development of children from approximately 500 Madison- and Milwaukee-area families.
In the current study, researchers measured methylation patterns in cheek-cell DNA collected from more than 100 adolescents at age 15. These patterns were compared to data obtained in 1990 and 1991, when these same children were infants and toddlers, and their parents were asked to report on their stress levels - including depression, family-expressed anger, parenting stress and financial stress.
The researchers, led by Michael S. Kobor, a University of British Columbia associate professor of medical genetics, found that higher stress levels reported by mothers during their child's first year correlated with methylation levels on 139 DNA sites in adolescents. They also discovered 31 sites that correlated with fathers' higher reported stress during their child's preschool years (3½ to 4½ years old).
"This is very exciting because we've shown that day-to-day stress in early childhood can predict changes in DNA that can be observed in adolescence," says Essex. "It's further proof of the importance of those early years and the lasting effects of children's family environments during infancy and preschool."
Her collaborators in British Columbia agreed.
"This seems to be the first demonstration, using carefully collected longitudinal data, that parental adversity during a child's first years leads to discernible changes in his or her 'epigenome,' measurable more than a decade later," says Kobor. "This literally provides a mechanism by which experiences 'get under the skin' to stay with us for a long time."
The team also found that fathers' stress level is more strongly associated with DNA methylation in daughters, while mothers' stress level has an effect with both boys and girls. This reinforces other research, including earlier work of Essex and colleagues, showing that the absence of fathers or their lack of participation in parenting is associated with an earlier onset of puberty and difficult temperamental traits in girls, but not in boys.
These results underscore the importance of considering gender and timing in understanding child development.
"As is often the case, some parenting effects appear to have similar outcomes for girls and boys, but others differ based on the gender of children and parents as well as the period of development under consideration," says Jeffrey Armstrong, study co-author and a UW researcher in psychiatry.
In general, none of the genes whose methylation level correlated with stress were among those best known to play a role in influencing a person's behavior or reaction to environmental stress. But they did find some genes that had a consistent change in methylation levels at more than one site on the DNA, including one involved in the production of insulin, the hormone that regulates blood sugar levels, and three other genes possibly involved in brain development.
The research was funded by the National Institute of Mental Health, the Canadian Institute for Advanced Research and the Djavad Mowafaghian Foundation.
Date Published: 08/30/2011