A FEW years ago, researchers in Montreal produced a disturbing finding. By the simple act of neglecting her young, a mother rat could permanently change the expression of genes in her offspring. Dams that licked their pups only infrequently—the rat equivalent of bad maternal care—sent their little ones off into the world with a more anxious disposition than rats with dams that had lavished care on them. What is more, this lack of attention, the researchers discovered, had chemically altered a gene controlling an important stress hormone.

It was a striking case of how nurture affects nature. And it made the researchers curious about whether the same could be happening in humans. Now, by studying the brains of suicide victims, they have begun to explore that question.

The field they are investigating is known as epigenetics. This is the interface between our genes, which are fixed, and our environment, which is ever-changing. Although people are born with a complement of genes that they are stuck with for life, those genes can be switched on and off—and this can make a world of difference. All the more harrowing, then, that simple things like dietary supplements and stress have been shown capable of throwing the switch.

Moshe Szyf and his colleagues at McGill University knew that around a fifth of people who die by their own hand suffered abuse in childhood. They found 13 such people whose brains had been donated to science, as well as the brains of 11 people who had died in accidents and had had normal happy childhoods. They compared the two groups.

Dr Szyf and his team looked at a gene that codes for ribosomal RNA, which helps control the manufacture of proteins. Protein synthesis is essential to the brain if it is going to generate new connections—in the process of learning something, say, or remembering it. They were especially interested in a part of the brain, the hippocampus, which is known to be influential in mood.

Genes get switched off when a chemical mark, a methyl group, is added to the DNA. When they examined these genes in the hippocampus, they discovered that, in the suicide group, many more of them had been methylated, or switched off; “frozen assets”, says Dr Szyf. In another part of the brain, the cerebellum, however, which is not involved in mood, there were no differences in the levels of methylation between the two groups. This suggests that the hypermethylation in the suicide group was not just a general difference, says Dr Szyf, but rather a response to something specific, such as abuse suffered in childhood. They published their findings this week in Public Library of Science (PLoS) ONE, an open-access scientific journal.

The research raises two big questions. Can altered methylation patterns be somehow detected in blood samples? Dr Szyf thinks so. He wonders if there may be clues in T cells, which are involved in immunity and which regularly communicate with the brain.

More important, though, if abuse in early life has caused hypermethylation, is whether there is any way to undo it. An intervention could be social, he says, or nutritional, or with drugs. Dr Szyf is hopeful: in the rats, at least, they were able to intervene and turn things around.