Understanding how genes change nicotine receptors may foster better treatments. Stitzel says, "No single gene is going to be the sole determinant of whether someone will become addicted to nicotine or any other substance, because addiction likely is due to the effects of many genes as well as social and other environmental factors."

However, he adds, "By identifying genes that contribute to whether an individual will become addicted, we will gain important knowledge about the biology of addiction. With that, we will be in a much better position to design more effective treatments for addiction. This approach may also lead to treatments tailored to the 'genetic profile' of the smoker."

The authors similarly determined that Chrna4 does not directly regulate alcohol intake because removal of Chrnb2, a gene whose protein partners with the Chrna4 protein, does not affect the relationship between Chrna4 and alcohol consumption. Therefore, Chrna4 may be associated with alcohol consumption through linkage to an as-yet undetermined gene that regulates alcohol intake. Stitzel concludes that, "Common genes likely play a part in why there is such a [strong] link between nicotine and ethanol intake, which in humans means smoking and drinking."

In addition, the finding could help to account for the tendency of smokers to "hand down" versions of genes that increase the likelihood of becoming a smoker. Stitzel says that about half of why a human becomes a smoker is genetically determined; the other half comes from environmental factors.

The second study, led by Juergen Hennig, PhD, at Germany's University of Giessen, added to a growing body of evidence that the type of aggressive behavior we think of as psychopathic or sociopathic has some genetic basis that may involve abnormally low levels of the neurotransmitter serotonin. Once again, gene polymorphisms appear to influence individual variance.

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6-Mar-2005