Genome complexity: human epigenetics (Introduction)

by David Turell , Monday, March 09, 2015, 23:11 (3329 days ago) @ David Turell

Children and grandchildren of Holocaust survivors have lower levels of stress hormones:-http://www.scientificamerican.com/article/descendants-of-holocaust-survivors-have-altered-stress-hormones/?WT.mc_id=SA_EVO_20150309-"It is not completely clear why survivors produce less cortisol, but Yehuda's team recently found that survivors also have low levels of an enzyme that breaks down cortisol. The adaptation makes sense: reducing enzyme activity keeps more free cortisol in the body, which allows the liver and kidneys to maximize stores of glucose and metabolic fuels—an optimal response to prolonged starvation and other threats. The younger the survivors were during World War II, the less of the enzyme they have as adults. This finding echoes the results of many other human epigenetic studies that show that the effects of certain experiences during childhood and adolescence are especially enduring in individuals and sometimes even across generations (right).-"Most recently, a new study looked at the descendants of the Holocaust survivors. Like their parents, many have low levels of cortisol, particularly if their mothers had PTSD. Yet unlike their parents, they have higher than normal levels of the cortisol-busting enzyme. Yehuda and her colleagues theorize that this adaptation happened in utero. The enzyme is usually present in high levels in the placenta to protect the fetus from the mother's circulating cortisol. If pregnant survivors had low levels of the enzyme in the placenta, a greater amount of cortisol could make its way to the fetus, which would then develop high levels of the enzyme to protect itself.-"Epigenetic changes often serve to biologically prepare offspring for an environment similar to that of the parents, Yehuda explains. In this case, however, the needs of the fetus seem to have trumped that goal. With low levels of cortisol and high levels of the enzyme that breaks it down, many descendants of Holocaust survivors would be ill adapted to survive starvation themselves. In fact, that stress hormone profile might make them more susceptible to PTSD (below, yellow); previous studies have indeed suggested that the offspring of Holocaust survivors are more vulnerable to the effects of stress and are more likely to experience symptoms of PTSD. These descendants may also be at risk for age-related metabolic syndromes, including obesity, hypertension and insulin resistance, particularly in an environment of plenty."