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Childhood Stress Leaves Genetic Scars
24 April 2012 2:19 pm
Traumatic experiences in early life can leave emotional scars. But a new study suggests that violence in childhood may leave a genetic mark as well. Researchers have found that children who are physically abused and bullied tend to have shorter telomeres—structures at the tips of chromosomes whose shrinkage has been linked to aging and disease.
Telomeres prevent DNA strands from unravelling, much like the plastic aglets on a shoelace. When cells divide, these structures grow shorter, limiting the number of times a cell can reproduce. For this reason, telomeres may reflect biological age. Research has found associations between stress and accelerated telomere loss, and shortened telomeres correlate with several health problems, including diabetes, dementia, and fatigue.
But the connection between telomere length and health and longevity is far from clear. "There's a lot of doubt in the field," notes Joao Passos, a cellular aging specialist at Newcastle University in the United Kingdom who was not involved in the research. "For as many studies that show telomere length as a good predictor of health outcomes, there are as many that find no relationship."
Also unclear is whether childhood stress can affect telomere length. Almost all recent work on the topic has used retrospective data—that is, adults' recollections about their past. The new study examined children who were under stress to determine if they have shorter telomeres.
To conduct it, a team of researchers at Duke University in Durham, North Carolina, used data from the Environmental Risk Longitudinal Twin Study, which has followed 1100 sets of British twins from birth to observe how genes and environment interact. In addition to gathering information about diet, education, and income, the scientists interviewed mothers about their children's experience of violence in the form of direct physical abuse, bullying, and exposure to parental domestic abuse.
The team selected 236 children, half of whom had experienced at least one form of violence. Using DNA samples collected at ages 5 and 10, the investigators measured telomere length using polymerase chain reaction to assess how many times a particular gene copied itself. The average number of times a gene replicated itself was lower among children who had experienced violence, the team reports today in Molecular Psychiatry, indicating a relationship between violence and shortened telomeres. In addition, the researchers found a significant association between the number of violent experiences and the amount of telomere loss.
"Children who experience physical violence appear to be aging at a faster rate," says neuroscientist and co-author Avshalom Caspi. As a result, he says, they may face increased risk of disease in adulthood and possibly shortened lifespan.
But the findings were not entirely grim. Among a small number of DNA samples drawn from children who had experienced violence before age 5 but not after, the researchers observed telomere growth. For children who experienced multiple incidents of violence between ages 5and 10, by contrast, the data showed a clear pattern of telomere loss. This finding could be a result of errors in the way telomeres were measured, says neurobiologist Idan Shalev, the lead author. But other studies suggest that making healthful life changes, such as reducing stress and exercising, can slow down the rate of telomere loss. Shalev suggests that improving a child's household environment might have the same effect in protecting telomeres.
Charles Nelson, a pediatric neuroscientist at Harvard Medical School in Boston, says scientists don't know whether it's possible to reverse telomere shortening. However, he says, "It will be interesting to see if this process will reverse itself if these children are removed from their abusive homes and placed with safe families."
Forthcoming research may provide an answer. Now that the children from the study are 18, the Duke team plans to measure their telomeres again to determine if shortening has slowed down, or even reversed, for children who were removed from stressful environments.
Psychologist Elissa Epel of the University of California, San Francisco, says that although questions loom large in this field of research, the work underscores the need to protect children. "Rather than assuming children are biologically resilient given their youth, such exposures leave imprints that may not just go away as we age."