Researchers following adolescent and pre-adolescent healthy daughters of mothers with a history of depression, have found that the chromosomes of these high-risk girls show signs of cellular aging.

In a paper published in the Sept. 30 edition of Molecular Psychiatry, Stanford scientists found that telomeres, the caps at the end of chromosomes whose length shortens as a person ages, are shorter than normal in girls whose mothers have had multiple episodes of depression.

What was especially surprising, according to these researchers, was that these 10-to-14  year-old girls with telomere shortening showed no signs or symptoms of depression at the beginning of the study, when their telomeres were measured.

"How could healthy 10- to 14-year-old girls show signs of aging?" asked Thomas Insel, the director of the National Institute of Mental Health, on his NIMH blog last month. "The answer is not entirely clear but . . . the same girls with shortened telomeres has increased stress reactivity, indicated by a steeper spike in the hormone cortisol in response to a simple stress test."

Insel notes that while there is a significant amount of research "linking developmental stress to risk for depression" -- as the study progressed, 60 percent of the girls at high risk, because of mothers diagnosed with depression, developed depression by the age of 18 -- the Stanford research suggests stress reactivity may be an important mechanism for cellular aging.

"Investigating the cause and timing of decreased telomere length -- to what extent it may result from abnormalities in stress responses or is genetically influenced, for example -- will be important for understanding the relationship between cellular aging, depression, and other medical conditions."

In the meantime, the head of the Stanford study, Ian Gotlib, and his colleagues are continuing their experiments with these high-risk girls by using neurofeedback to try to retrain their brains to better handle stress responses.

"It will be a few years before we will know how much this intervention reduces risk for depression," Insel wrote, "but anything that prevents or slows the telomere shortening may be an early indication of success."