"The shared heritability between smoking and alcoholism, particularly in heavy smokers and heavy drinkers, indicates that some genes predispose individuals to both smoking and drinking," said Mary-Anne Enoch, a staff scientist in the Laboratory of Neurogenetics at the National Institute on Alcohol Abuse and Alcoholism and corresponding author for the study. "Nicotine's effects on the brain occur mainly through nicotinic acetylcholine receptors, and alcohol acts on these same receptors to release dopamine, the 'pleasure' hormone in the brain's reward pathway."
Enoch added that the enzyme COMT plays an important role in the breakdown of dopamine and norepinephrine in the brain, its activity varying according to a common COMT polymorphism, Val158Met. "The Met allele results in a less efficient enzyme and therefore probably more dopamine and norepinephrine in the brain," she said. "The Met allele has also been associated with increased anxiety and neuroticism, increased emotionality in response to pain, and greater brain activation in response to unpleasant visual images."
Whereas studies of European men have shown that the Met allele is associated with late onset alcoholism and increased alcohol intake in social drinkers, Enoch and her colleagues have found that in American Indians the Met allele was protective against alcoholism, and the Val allele was the risk allele.
"The answer to this paradox may lie in the relationship between anxiety and drinking patte
Source:Alcoholism: Clinical & Experimental Research