Children who have been abused or neglected early in life are at risk for developing both emotional and physical health problems, according to a recent study.

Researchers from the University of Wisconsin, Madison found that maltreatment affects the way genes are activated, which has implications for children's long-term development. They found an association between the kind of parenting children had and a particular gene (called the glucocorticoid receptor gene) that's responsible for crucial aspects of social functioning and health.

"This link between early life stress and changes in genes may uncover how early childhood experiences get under the skin and confer lifelong risk," Seth Pollak, leader of the study, said in a statement.

For the study, the researchers examined DNA methylation in the blood of 56 children ages 11 to 14. Half of the children had been physically abused.

They found no differences in the genes that the children were born with; instead, the differences were seen in the extent to which the genes had been turned on or off.

Previous studies have shown that children who have experienced physical abuse, sexual abuse, and neglect are more likely to develop mood, anxiety, and aggressive disorders, as well as to have problems regulating their emotions. These problems, in turn, can disrupt relationships and affect school performance. Maltreated children are also at risk for chronic health problems such as cardiac disease and cancer. The current study helps explain why these childhood experiences can affect health years later.

The gene identified by the researchers affects the hypothalamic-pituitary-adrenal (HPA) axis in rodents. Disruptions of this system in the brain would make it difficult for people to regulate their emotional behavior and stress levels. Circulating through the body in the blood, this gene affects the immune system, leaving individuals less able to fight off germs and more vulnerable to illnesses.

"Our finding that children who were physically maltreated display a specific change to the glucocorticoid receptor gene could explain why abused children have more emotional difficulties as they age," Pollak said. "They may have fewer glucocorticoid receptors in their brains, which would impair the brain's stress-response system and result in problems regulating stress."

Researchers said the findings have implications for designing more effective interventions for children, especially since studies of animals indicate that the effects of poor parenting on gene methylation may be reversible if caregiving improves.

The findings were recently published in the journal Child Development.