Drinking too much alcohol may be caused by a gene which makes a pint of beer or glass more pleasurable than it should be, scientists claim.
Tens of thousands of people had their genome analysed to investigate whether their DNA affects how much alcohol they consume.
Researchers found those who drink a lot – at least five bottles of wine a week for men, and three-and-a-half for women – shared six specific genetic variants.
These twists in DNA may disrupt pathways involved in reward and pleasure, causing them to enjoy a tipple more than the next person.
Drinking habits are known to be rooted somewhat in a person’s genetic makeup. Pinpointing the specific locations could lead to better treatment of alcohol use disorder (AUD), which is when drinking is so extreme it causes harm.
AUD has shown to be half the fault of genetics, while the other half is dependent on environmental factors, such as the age someone had their first drink.
The disorder has been implicated in the development of more than 60 diseases, including liver disease, heart disease and cancer.
Around 14million adult Americans battle AUD, and 1.6million adultsin the UK have some level of dependence, figures show.
The study, in the journal Science Advances, was led by Dr Andrew Thompson and Professor Sir Munir Pirmohamed from the University of Liverpool.
Some 125,000 British people aged 40 to 69 were involved in the analysis. Their lifestyle data and blood samples were given to the UK Biobank.
All participants had been asked to quantify how much alcohol they consumed per week or per month – for example, how many glasses of red wine per week.
The researchers calculated the number of units each person drank per week using UK guidelines.
Heavy drinkers were defined as men who drank more than 50 units a week and women who drank more than 35 units per week.
A bottle of wine contains around 10 units, while a can of lager with five per cent alcohol contains two units.
Each person’s genome was scanned in search for small DNA variations called SNPs.
There are millions of SNPs, but if a particular SNP occurs more frequently in people with a particular condition than in people without the condition, it can suggest the underlying reason for the difference.
Results showed altered levels of six SNPs in heavy drinkers, some of which have been identified in research before.
One gene, DRD2, is implicated in the feeling of pleasure and reward. Another, KLB, may also make alcohol and sugary foods more enjoyable.
Low levels of ADH1B was also linked to heavy drinkers, and is one of the most robustly studied genes in this area.
ADH1B encodes for enzymes which break alcohol down. As alcohol is metabolised, it causes unpleasant side effects, like nausea and a high heart rate.
People with low levels of ADH1B metabolise slower, therefore don’t get that nauseating drunk feeling as quick. They may be able to consume more alcohol over longer periods of time.
The risk for high alcohol consumption may share genetic links with risk for gout, a form of arthritis, high blood pressure, cancer and type 2 diabetes.
To test the researchers’ findings, worms were genetically engineered to carry some of the identified genes.
Worms are considered ‘excellent’ models for investigating the effects of alcohol because they behave in a similar way when intoxicated.
The genetically engineered worms had a significantly different response to alcohol compared to wild worms, based on the co-ordination of their movements.
The scientists said these findings reinforce the link between genetic predisposition and heavy drinking tendencies in humans.
However, the effects were reduced if the genes were switched off.
Dr Thompson, said: ‘Our study offers insight into genes, pathways, and relationships for disease risk associated with high alcohol consumption.
‘This improved understanding regarding genetic risk of alcohol consumption will lead to further study and hopefully opportunities to develop new treatments for people with alcohol use disorders.’
Professor Pirmohamed, said: ‘This is a really important area because of the morbidity and mortality, and societal effects, of heavy alcohol consumption.’
Ian Hamilton, a senior lecturer in addiction at York University, who was not involved in the research, said identifying genes related to alcohol use is challenging.
He told MailOnline: ‘We have known for some time that there is a link between genes and problem drinking but identifying specific genes has proved to be difficult.
‘This research is another step in understanding which genes play a part and how this relationship works at a biological level.
‘Although these findings won’t have an impact on treatment today they could be used in the development of new treatments in the future.’
The researchers acknowledged that the study relied on self-reported data about alcohol use, which may be wrong.