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Does having alcoholic parents make you more susceptible to alcohol problems? Why do some people develop drink or drug problems while others in the same family do not? How much can genetic research tell us about why drink and drugs can affect people in so many different ways? With genetic research discovering increasing links with behaviour we invited two of the leading addiction and gene researchers to explain the science. Tamara Phillips and John Crabbe uncover the everemerging world of genetic research and addiction theory.
Genes, through their products (such as proteins that may be enzymes, receptors or hormones), influence the course of addiction, and the risk for alcoholism and drug abuse. Classical genetic methods suggest that about half of an individual's risk for substance abuse can be traced to his or her genes. In humans, studies using twins and adopted individuals show that having many substance abusers in your immediate family increases the probability that a given individual will be a substance abuser, even if that individual is raised in a non-substance abusing family situation (Edenberg & Kranzler, 2005).
Laboratory animal studies with different mouse strains (somewhat like dog breeds) show that mice of some strains like alcohol, and those of other strains don't (for example Belknap et al, 1993). Further, animals have been bred to be highly drugsusceptible using much the same techniques used to breed cattle for the quality of their milk.
That one can breed for high and low alcohol preference (see Grahame et al, 1999; Phillips et al, 2005), or high and low sensitivity to the stimulating effects of methamphetamine (Kamens et al, 2005), indicates that there is a genetic influence on these traits.
Genes are not, however, destiny. The other half of one's risk is non-genetic, or environmental; even a highly unfavourable genetic inheritance can, and often does, lead to a non-dependent life course. On the other hand, many individuals with virtually no discernible genetic risk develop serious drug habits.
Because we already know that genes influence the probability of developing an addiction, one goal of genetic studies has been to identify which genes make people more (or less) vulnerable. Progress in identifying the influential genes has been accelerated by the development of new-era genetic models and techniques.