New research has found a strong link between alcohol dependence and a genetic variation called copy number variations on chromosome 5q13.2.
Previous studies have shown that genetics play a significant role in making a person dependent on alcohol or drugs.
Experts say that these genetic traits are heritable. Heritability range falls between 50 and 60 percent for both men and women.
"Twin and adoption studies have estimated the heritability of alcohol dependence or AD – the proportion of variability in risk that is due to genetic factors – to be to be about 50 percent," said John P. Rice, professor of mathematics in psychiatry at Washington University and author for the study.
Symptoms for Alcohol dependence or alcoholism include loss of control, craving and the need to drink higher amounts of alcohol to get "high". Additionally the person might have withdrawal symptoms like nausea, shakiness and anxiety after stopping drinking, says National Institute on Alcohol Abuse and Alcoholism.
"Alcoholism's pervasive impact on public health and its heritability make searches for genes influencing vulnerability a priority. Although only a few genes influencing alcoholism risk have been discovered so far, we can expect this picture to change rapidly as more powerful genomic tools, including genotyping arrays and next-generation sequencing, are applied, and as geneticists become ever more ambitious in the size and phenotypic depth of the populations they study," said David Goldman, chief of the lab of neurogenetics at the National Institute on Alcohol Abuse and Alcoholism.
A study from 1999 said that the genetic factors for both alcohol and nicotine dependence are the same which is why most alcohol dependents end up as chain smokers as well.
"We found two CNVs – on chromosomes 5q13.2 and 6q14.1 – that were associated with AD. For both CNVs, AD cases tended to have more duplications than controls without AD. These two CNVs are statistically significant but the effect on risk is modest. The region identified on chromosome 5 contains several genes that have been implicated is rare neurological disorders and play a role in the nervous system. It will be a challenge to understand what gene(s) are causing this association and how they work to increase one's risk for AD," said Rice.
For the study, researchers interviewed nearly 4000 participants using Semi-Structured Assessment for the Genetics of Alcoholism. Later, almost 2,500 participants were chosen for further genetic testing.
"This is a carefully done study and results are conservatively interpreted. The association to the 5q13.2 region is highly significant statistically, but further it is compelling that the region they have found is one that plays a role in other neurologic disorders. The chromosome 6 findings are statistically more highly significant but more difficult to pursue because the region involved is a gene desert. It will be fascinating to see the outcome of efforts to replicate these findings in other populations and validate through other means, for example, by studies of the individual genes in the regions involved in the CNVs," said Rice.
Experts say that genetic vulnerability does not always mean that the person will become alcoholic. Environment plays an equally important role in determining what genes will be expressed.
"Our results need to be replicated in independent samples. If they hold, then researchers who study the basic biology of how changes in the genome lead to increased or decreased risk for illness can add to our understanding. It is important to note that the associations are modest, so these findings cannot be used to predict who will become an alcoholic. The results open up a new line of investigation, but it can take many years before we have a true understanding," he said.
Alcoholism and related problems result in some 79,000 deaths in the U.S., according to the Centers for Disease Control and Prevention.
"These findings are indicative of the increasing pace of genetic and genomic research on alcoholism. However, the findings are at least several years removed from clinical impact, except in the sense of showing that alcoholism is a biomedical disease whose genetic influences are beginning to be understood," added Goldman.
The study is available in the journal Alcoholism: Clinical & Experimental Research.