Why can’t your friend “just get over” her upbringing by an angry, distant mother? Why can’t she “just snap out of it”? The reason may well be due to methyl groups that were added in childhood to genes in her brain, thereby handcuffing her mood to feelings of fear and despair.
Of course, it is generally not possible to sample the brains of living people. But examining blood samples in humans is routine, and Szyf has gone searching there for markers of epigenetic methylation. Sure enough, in 2011 he reported on a genome-wide analysis of blood samples taken from 40 men who participated in a British study of people born in England in 1958.
All the men had been at a socioeconomic extreme, either very rich or very poor, at some point in their lives ranging from early childhood to mid-adulthood. In all, Szyf analyzed the methylation state of about 20,000 genes. Of these, 6,176 genes varied significantly based on poverty or wealth. Most striking, however, was the finding that genes were more than twice as likely to show methylation changes based on family income during early childhood versus economic status as adults.
Timing, in other words, matters. Your parents winning the lottery or going bankrupt when you’re 2 years old will likely affect the epigenome of your brain, and your resulting emotional tendencies, far more strongly than whatever fortune finds you in middle age.
Last year, Szyf and researchers from Yale University published another study of human blood samples, comparing 14 children raised in Russian orphanages with 14 other Russian children raised by their biological parents. They found far more methylation in the orphans’ genes, including many that play an important role in neural communication and brain development and function.
“Our study shows that the early stress of separation from a biological parent impacts long-term programming of genome function; this might explain why adopted children may be particularly vulnerable to harsh parenting in terms of their physical and mental health,” said Szyf’s co-author, psychologist Elena Grigorenko of the Child Study Center at Yale. “Parenting adopted children might require much more nurturing care to reverse these changes in genome regulation.”
A case study in the epigenetic effects of upbringing in humans can be seen in the life of Szyf’s and Meaney’s onetime collaborator, Frances Champagne. “My mom studied prolactin, a hormone involved in maternal behavior. She was a driving force in encouraging me to go into science,” she recalls. Now a leading figure in the study of maternal influence, Champagne just had her first child, a daughter. And epigenetic research has taught her something not found in the What to Expect books or even her mother’s former lab.
“The thing I’ve gained from the work I do is that stress is a big suppressor of maternal behavior,” she says. “We see it in the animal studies, and it’s true in humans. So the best thing you can do is not to worry all the time about whether you’re doing the right thing. Keeping the stress level down is the most important thing. And tactile interaction — that’s certainly what the good mother rats are doing with their babies. That sensory input, the touching, is so important for the developing brain.”
The Mark Of Cain
The message that a mother’s love can make all the difference in a child’s life is nothing new. But the ability of epigenetic change to persist across generations remains the subject of debate. Is methylation transmitted directly through the fertilized egg, or is each infant born pure, a methylated virgin, with the attachments of methyl groups slathered on solely by parents after birth?
Neuroscientist Eric Nestler of the Icahn School of Medicine at Mount Sinai in New York has been seeking an answer for years. In one study, he exposed male mice to 10 days of bullying by larger, more aggressive mice. At the end of the experiment, the bullied mice were socially withdrawn.
To test whether such effects could be transmitted to the next generation, Nestler took another group of bullied mice and bred them with females, but kept them from ever meeting their offspring.