If you just can't seem to kick the smoking habit, it might be down to your genes, a new study has found. Researchers in China have been studying the impact of a gene called ANKK1, and have identified variations in its structure that could make it harder to fight certain types of addiction.

Research has shown that ANKK1 helps identify the release of dopamine into the brain's reward centres, which reinforces useful behaviours. But addictive drugs - including nicotine - also cause dopamine levels to spike. Because ANKK1 is so closely linked to how our bodies react to addictions, it's likely also having an influence over how easy they are to quit.

One small part of ANKK1 can vary based on the genes we inherit from our parents. There are two versions of this fragment, A1 and A2, so we can be left with either A1/A1, A1/A2 or A2/A2.

The new research from Zhejiang University found that those with the A2/A2 combination have better odds of kicking the smoking habit, based on data from 23 different studies published between 1994 and 2014, covering a total of 11,151 current and former smokers. All of these participants had their DNA tested, so the team could see which version of the ANKK1 gene they had.

Turns out those with A2/A2 in their DNA make-up were 22 percent more likely to successfully quit smoking - although only in people of Caucasian descent. For smokers of East Asian descent, the gene variations seemed to make no difference in the likelihood of being able to quit, and there were not enough black and Latino smokers in the study to determine if there was a similar link. 

A2/A2 was found to be the most common genotype in Caucasians, with 62.5 percent of them having it - that means it's possible that up to one-third of people have the gene variants - A1/A1 or A1/A2 - that make it harder for them to quit cigarettes.

New Scientist reports:

"People carrying these versions of ANKK1 may need more aggressive strategies to fight their addiction to cigarettes, says Li. The A1/A1 and A1/A2 gene variations have also been linked to obesity and drug addiction, which suggests they may predispose people to addictive behaviours."

The researchers are hoping that their findings can help improve the drugs used to help people kick the smoking habit by allowing them to be tailored for particular gene types.

"Our results provide supportive evidence for further investigation of personalised medicine for smoking cessation according to individual genotypes," they conclude. "However, research on this problem remains in its infancy, so more well-designed genetic association, pharmacogenetic and molecular functional studies are warranted."

The paper has been published in the journal Translational Psychiatry.