As noted in my previous post, the impact of alcohol on brain maturation in adolescence is still considered an open question, although studies indicate that early exposure to alcohol is even more damaging in adolescence than in adulthood. It’s not surprising at all. Alcohol crosses the blood-brain barrier to influence the function of neurons. Actually, influence is not the right term: intoxicates or poisons the brain is more correct. After all, the effect of alcohol on your state of mind is due to a state of intoxication.Alcohol is of course only one of many substances that have an impact on brain function, and that are used for recreational purposes. Other psychoactive substances include nicotine/tobacco, cannabis, cocaine and LSD. In a population of adolescents the young vary in their use of such drugs, both the debut, the regularity of use, and the combined – or polydrug – use. The question is, then, what causes this variation?
In a special issue of Behavioral Genetics the genetic and environmental causes of substance use are explored and reviewed. For example, Jason Pagan and colleagues study the causes of alcohol use in adolescence, and conclude that
(…) there was no significant evidence of shared environmental influences on alcohol problems in early adulthood. Problems were largely influenced by genetic factors that overlapped with genetic influences on frequency of use. Unique environmental factors were largely specific to each stage, with some overlap between alcohol problems and frequency of use at age 25.
Danielle Dick and her colleagues, on the other hand, find that a specific gene, GABRA2, shows two specific patterns in relation to adolescent and adult alcohol abuse. First they found that aconsistent elevation in risk for alcohol dependence associated with GABRA2 is not evident until the mid-20s and then remains throughout adulthood. On the other hand, GABRA2 was also associated with other drug dependence in their sample, both in adolescence and adulthood. So this gene can indeed be a causative factor in the forming of drug use in general, which some findings seem to indicate. GABRA2 has been shown several times to be coupled to alcoholism. For example, Danielle Dick herself has published data showing a complex relationship between martial status, alcohol dependence and GABRA2, concluding in another publication this year:
These analyses provide evidence of both gene-environment correlation and gene-environment interaction associated with GABRA2, marital status, and alcohol dependence. They illustrate the complex pathways by which genotype and environmental risk factors act and interact to influence alcohol dependence and challenge traditional conceptualizations of “environmental” risk factors.
Anyway, the special issue in Behavior Genetics has several good articles on the gene-environment interaction effects on the development of substance use disorders. It’s a must-read to anyone interested in genes, brain and behaviour.