A newly discovered addiction gene could be fuelling teenage binge-drinking, research suggests.
The mutant version of the RASGRF2 gene makes the brain more sensitive to habit-forming rewards such as alcohol, studies have shown.
In both mice and young teenage boys it was closely linked to alcohol-seeking behaviour.
A group of 16-year-olds with the genetic variant drank alcohol more frequently than boys who did not possess it.
Lead scientist Professor Gunter Schumann, from the Institute of Psychiatry at King's College London, said: "People seek out situations which fulfil their sense of reward and make them happy, so if your brain is wired to find alcohol rewarding, you will seek it out.
"We now understand the chain of action: how our genes shape this function in our brains and how that, in turn, leads to human behaviour.
"We found that the RASGRF2 gene plays a crucial role in controlling how alcohol stimulates the brain to release dopamine (a nerve signalling molecule), and hence trigger the feeling of reward. So, if people have a genetic variation of the RASGRF2 gene, alcohol gives them a stronger sense of reward, making them more likely to be heavy drinkers."
Around six in 10 young people aged 11 to 15 in England consume alcohol, a proportion that has remained relatively stable for 20 years.
However, rates of teenage binge drinking have soared in recent years. Teenagers drank an average of six units of alcohol per week in 1994 and 13 units in 2007. A unit of alcohol is roughly equivalent to half a pint of beer or a small glass of wine.
Each year some 5,000 teenagers in the UK are admitted to hospital for alcohol-related reasons.
Teenage alcohol abuse is linked to poor brain development, future health problems, and risk taking and antisocial behaviour, the scientists pointed out.
Prof Schumann's team, whose findings are reported in the journal Proceedings of the National Academy of Sciences, first focused on the RASGRF2 gene in mice.
Mice missing the gene were significantly less driven to seek out alcohol after initial exposure to the substance.
Lack of RASGRF2 impaired reward signalling in a part of the brain called the ventral tegmental area (VTA).
Those with the RASGRF2 variant showed greater activation of a brain area that helps control dopamine release when anticipating a reward. This suggests a link between the gene variant and reward-seeking, or addiction-driven, behaviour.
At 16 years old, the same group of boys were studied again. By this time many had already started to drink frequently.
The research confirmed that those with the RASGRF2 variant consumed alcohol the most often.