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Researchers closing in on addiction genes

Researchers think the amount people smoke and how dependent they become is largely genetic. Image: Shutterstock/ Stefano Carnevali
Researchers think the amount people smoke and how dependent they become is largely genetic. Image: Shutterstock/ Stefano Carnevali

Falling in with the wrong crowd at school or college can lead some young people astray but not others – now researchers are closing in on the addiction genes that determine whether bad habits stick.

Whether it’s cigarettes behind the bike sheds or pizza and fried chicken every night, researchers believe that many of our bad habits are down to our genes.

‘If you initiate smoking, then the amount of cigarettes you smoke and whether you become dependent or not, that is already determined in your genes when you are born,’ said Dr Jacqueline Mignon Vink, principal investigator of the European Research Council-funded Beyond the Genetics of Addiction project.

According to Dr Vink, based at the department of Biological Psychology at VU University in the Netherlands, whether or not you start smoking is largely down to your environment, but it’s your genes that determine your chances of getting hooked – from how much you smoke to how addicted you become.

‘If you initiate smoking, then the amount of cigarettes you smoke and whether you become dependent or not, that is already determined in your genes when you are born.’

Dr Jacqueline Mignon Vink, VU University, the Netherlands

Factors in the environment around you as you grow up, such as the school you go to, your peer group and your family – for instance whether your parents or older siblings smoke – are some of the main triggers for starting smoking. But it’s genetics that comes into play after you’ve smoked the first cigarette.

The point is that if both your parents smoke, it is likely to be down to their DNA. ‘If your parents are both smokers, there’s a very high chance you share the smoking genes inherited from your parents,’ Dr Vink explained.

The project is using data from the Netherlands Twin Register to find the genes involved in substance addiction. By comparing data from twins who are genetically identical and from non-identical twins – who share around half of their DNA – scientists are able to show that similarities in substance use between identical twins are likely to stem from genetic factors.

Enjoyable

Dr Vink previously contributed to a large genome-wide association study of 67 000 participants that led to the discovery of a cluster of nicotine receptor genes in the DNA. These receptor genes are connected with the number of cigarettes a person smokes, and the more receptors you have the more enjoyable smoking is. According to Dr Vink, as much as 75 % of the variation in people’s nicotine habit is down to their genes.

It provides a starting point for researchers to begin developing anti-smoking drugs. ‘You could, for example, develop medicines that interact with these gene expressions so that people do not get that pleasurable feeling anymore,’ Dr Vink said. ‘But that's only possible if you really know the exact biological mechansims.’

Now, one of the project’s main goals is to unravel the genes involved in cannabis use. The latest study brings together 11 research teams, with data from over 13 000 participants. While no genome-wide significant results have been found yet, one of the next steps is to incorporate the age of initiation into the study, ‘because young age is a known risk factor for later problems for cannabis abuse and other drug use’, she said.

Unlike addiction to substances such as nicotine or cannabis, researchers on the EU-funded NeuroFAST project suggest there is currently insufficient evidence to support the idea that food ingredients cause addiction, but that overeating itself should be considered as a behavioural addiction.

‘It’s a natural behavioural disorder where people show addictive-like behaviour towards foods in full knowledge of the harm to their health,’ said Professor Suzanne Dickson, coordinator of the project at the University of Gothenburg, Sweden. The project, whose consensus opinion on food addiction was published in the journal Neuroscience and Biobehavioural Reviews in September, is set to conclude in 2015.

Prof. Dickson believes that some people are more prone to developing the craving for food. ‘There’s going to be genetically vulnerable individuals who if they’re in the wrong environment will suffer,’ she said.

Humans have a genetic basis for wanting to eat as much as possible, which is inherited from our ancestors who ate food without knowing when the next meal would come, therefore eating even when feeling full made sense.

But in today’s world, where foods high in fat, salt and sugar are cheap and abundant, temptation is all around, and some people are less resistant to it than others.

‘It’s very easy to understand that in our modern obesogenic environment (where we are encouraged to eat unhealthily) people don’t have sufficient stop signals. It’s the way we were designed, it’s about survival,’ Prof. Dickson said.

NeuroFAST researchers are looking at the role that gut hormones such as grehlin have in eating addiction. They believe these hormones, which are released into the blood before you eat and trigger a sense of anticipation and reward in the brain, could be linked to addictive eating behaviour.

Better understanding of how they work in people who overeat could enable the development of drugs that block these hormones, and help people eat less.

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