YOUR LIFESTYLE: HOW EASY would it be to blame all your ills on the DNA you were born with? It's tempting, but not that straightforward, writes CLAIRE O'CONNELL
Genetic diseases aside, the information you hold in your genes has an impact on your general health – but their effects on your wellbeing are often down to how they are switched on or off.
And the good news emerging from research is that we could have some degree of control over that.
Take obesity: scientists have now pinpointed a number of gene variants associated with overloading the bathroom scales.
But before you resign yourself to having tubby DNA and washing down that triple cheeseburger with a hot fudge sundae, stop and chew on this: your genes can be marked by your environment – and that includes those burger and ice-cream spectaculars.
Scientists have long recognised that the environment can affect gene expression, but now they know how it happens at a chemical level.
It turns out that our genes can be literally tagged so they don’t switch on, and this tagging process is influenced not only by what we physically put into our bodies, such as food and tobacco smoke, but also by social factors, such as stress and child abuse.
It’s a complex picture, but what we are learning about gene expression now could help refine how we diagnose and manage many health conditions in the future.
You have a unique sequence of information called a genome encoded in your DNA, and the billions of cells that make up your body each contain a copy of it.
Within that DNA, around 25,000 genes contain information about how to make particular proteins – the basic building blocks of your body. And how those proteins function and interact can have a huge impact on your health.
“Every cell in our body is directed by the genes that we have. It’s the code for the colour of our eyes as well as how our brain is functioning,” explains Richard Tremblay, professor of child development at University College Dublin.
“To a certain extent that genetic code determines what we will become. But it also depends on the environment in which it is. And a human is made up of genes and environment – one can’t go without the other.”
But how can our environment orchestrate our genes? One of the key mechanisms is a chemical process called methylation, explains Prof Tremblay, where tiny molecules called ‘methyl groups’ are tagged on to DNA and stop particular genes from being switched on.
The pattern of gene methylation, which changes as we age and is altered in diseases like cancer, can be influenced by what we eat, drink and smoke, he notes: “Almost anything in the environment can have an impact on the methyl groups, including nicotine and alcohol.”
Of particular interest is how our early environment shapes our long-term health and even that of future generations, according to Tremblay, who cites obesity as an example.
“Epigenetic studies are leading to the idea that the present obesity epidemic could be partly an epigenetic phenomenon, where obesity during pregnancy affects gene expression of the foetus, making the child more likely to be obese. Then the daughters are more likely to transmit this problem to the next generation,” he says, noting that the need to increasing the quality of the environment in pregnancy and early childhood to help prevent long-term problems related to gene expression.
It’s not just what we eat or drink – social behaviour also seems to affect how our DNA gets tagged and in turn how gene activity gets ramped up or down.
Research in Canada has shown that rat pups licked by their mother at birth had higher levels of gene expression than pups that were not licked, notes Tremblay. “We are talking about thousands of genes that are affected simply by licking,” he says.
More ominously, studies have also found links between DNA methylation and the long-term impact of child abuse, including suicide, according to Dr Patrick McGowan from McGill University in Montreal.
“We know that events in early childhood - particularly abuse or severe neglect - have a strong impact on later health outcomes like depression and are strongly associated with suicide risk,” says McGowan. “There is also a lot of evidence that gene expression is altered in the brains of suicide victims. So the question we addressed was: how?”
By looking at post-mortem brain samples, his work found that people who had been abused and later killed themselves had greater levels of tagging on a stress-response related gene.
“Suicide victims with a history of childhood abuse had a substantial increase in the number of methyl groups in the , and this was associated with a decrease in gene transcription. So we are seeing an effect of early abuse on brain function,” explains McGowan, who adds that more studies are needed on this phenomenon.
But while our understanding of DNA methylation and its long-term effects is in its infancy, McGowan believes it will ultimately open up several new avenues relating to health.
“It has been very clear to scientists for some time that there is no ‘nature versus nurture’, rather it is a question of nature via nurture. Epigenetics may provide an answer as to how this occurs,” he explains.
“And I think the field will likely have a huge impact on how people think about environmental impacts on health outcomes, from the food we eat to education to therapeutics.
“Essentially, genes are not destiny – and I think that’s a very positive message.”