Historical trauma transmitted biologically?

A PBS NOVA program may explain how the disease and hunger experienced by Indians generations ago affects their descendants today.

Ghost in Your Genes--TV Program DescriptionScientists have long puzzled over the different fates of identical twins: both have the same genes, yet only one may develop a serious disease like cancer or autism. What's going on? Does something else besides genes determine who we are? NOVA explores this startling possibility in this program.

The "something else" turns out to be a network of chemical switches that sit on our DNA, turning genes off and on. Called collectively the epigenome, the switches appear to play a major role in everything from how our cells keep their identity to whether we contract dread diseases. Epigenetic switches may even help mold our personalities—or so it appears to Canadian researchers studying a group of epigenetically modified rats.

"We're in the midst of probably the biggest revolution in biology, which is going to forever transform the way we understand genetics, environment, the way the two interact, and what causes disease," says Mark Mehler, Professor of Neurology at Albert Einstein College of Medicine. "It's another level of biology, which for the first time really is up to the task of explaining the biological complexity of life."And:The program closes at the controversial cutting edge of this burgeoning new field. At the M. D. Anderson Cancer Center in Houston, Texas, researchers are investigating epigenetic means to treat a deadly form of leukemia (see Epigenetic Therapy). In Washington State, a researcher finds that a toxin given to rats still affects their offspring four generations later, without producing any changes in their genes. And in Sweden, a study of historical records seems to show that the lifespan of grandchildren is affected by their grandparents' access to food.

Might these effects be epigenetic? Might our experiences, by changing our epigenomes, literally change the fate of our offspring ... and their offspring ... and theirs in turn? And might our own states of health owe something to the diets and exposures of our forebears?

Some researchers are already convinced. "You live your life as a sort of ... guardian of your genome," says Marcus Pembrey of the Institute of Child Health at University College London, a co-investigator in the Swedish study. "It seems to me you've got to be careful of it because it's not just you. You can't be selfish ... you can't say, 'Well, I'll smoke' or 'I'll do whatever it is because I'm prepared to die early.' You're also looking after it for your children and grandchildren...." Epigenetics, Pembrey says, "is changing the way we think about inheritance forever."Some quotes from the show about research on Swedish villagers:

Ghost in Your Genes--TranscriptNARRATOR:  Overkalix offered Pembrey a unique opportunity to see if the events that happened in one generation could affect another decades later.

MARCUS PEMBREY:  Olly first reported that the food supply of the ancestors was affecting the longevity or mortality rate of the grandchildren, so I was very excited.And:NARRATOR:  This was one of the first indications that an environmental exposure in a man, one that did not cause a genetic mutation, could directly affect his male offspring.

MARCUS PEMBREY:  It really did look as if there was some new mechanism transmitting environmental exposure information from one generation to the next.And:MARCUS PEMBREY:  Once I had plotted out the full extent of those results, it was so beautiful and such a clear pattern, I knew then, quite definitely, that we were dealing with a trans-generational response. It was so coherent—and that's important in science, that the effect was coherent in some way—was tying in when eggs and sperm were being formed.

NARRATOR:  The diagram showed a significant link between generations, between the diet in one and the life expectancy of another.And:NARRATOR:  It raises a tantalizing prospect: that the impact of famine can be captured by the genes, in the egg and sperm, and that the memory of this event could be carried forward to affect grandchildren two generations later.

MARCUS PEMBREY:  We are changing the view of what inheritance is. You can't, in life, in ordinary development and living, separate out the gene from the environmental effect. They're so intertwined.And:MICHAEL SKINNER:  What this means, then, is what your grandmother was exposed to when she was pregnant could cause a disease in you—even though you've had no exposure—and you're going to pass it on to your great-grandchildren.

NARRATOR:  And if a pesticide can generate such effects, what about stress, smoking, drinking? To some, the epigenetic evidence is compelling enough already to warrant a public note of caution.Comment:  This could help explain the concept of intergenerational trauma. The evidence suggests that the effects of physical hardship may be transmitted biologically as well as culturally.