Research published in Nature Neuroscience last week shows that child abuse can alter the expression of a gene that regulates the way the brain controls the stress response. The study was conducted by researchers at the Douglas Mental Health University Institute and McGill University in Montreal, Canada, and the Singapore Institute for Clinical Sciences. Lead author Dr Patrick McGowan and his colleagues came to their conclusions after comparisons between samples collected posthumously from the hippocampi of brains of abused suicide victims, suicide victims who had not been abused, and people who had died in accidents and had no history of abuse.
The team found reduced activity of the gene for the glucocorticoid receptor - NC3R1 - in victims of child abuse. And they showed this reduced activity leads to fewer glucocorticoid receptors. Under stress the body produces the hormone cortisol which prepares us for fight-or-flight action. But extended exposure to cortisol can have damaging effects and so receptors to absorb the hormone are necessary to protect the brain. The researchers found that the genes that code for these receptors were about 40 per cent less active in people who had been abused as children than in those who had not. This is likely to explain a feeling of permanent stress, or anxiety, even when no stressors are present in the environment and people showing this gene expression would have had an abnormally heightened response to stress.
The differences seen were 'epigenetic' meaning that the DNA was not altered but instead this particular gene is marked with chemicals that determine how it functions. How long-lasting these alterations are in expression is unknown but could be permanent. This study is one of the first to show epigenetic evidence for a link between childhood abuse and long term psychological problems.
Co-author Dr Gustavo Turecki said 'we know from clinical experience that a difficult childhood can have an impact on the course of a person's life.' His colleague Moshe Szyf added, 'now we are starting to understand the biological implications of such psychological abuse.'