Gene Increases Risk For Pot Addiction

Danish researchers discovered a new gene which increases risk of cannabis addiction disorder.

People who consume cannabis, which is the most widely used illegal substance, experience cravings and withdrawals. The combination of genetic and environment factors is what causes substance abuse. But, so far, no genetic factor has been found.

The Danish researchers identified a single variant of the gene CHRNA2 (cholinergic receptor nicotinic a2 subunit), which affects the risk of becoming addicted to cannabis. This gene was found by studying the genomes more than 2000 people who have it and nearly 50,000 others without. Nature Neuroscience published the findings June 17. The researchers also compared it to a list of Icelandic volunteers that included nearly 50,000 people who have cannabis use disorder with 5,500 others without.

The gene doesn't make someone a pot smoker, but it can increase the risk of addiction for those who try cannabis, says Ditte Demontis, an associate professor at Aarhus University in Denmark, who led the work.

Demontis hopes to be able to identify genes that are involved in the disease and eventually develop a treatment. She believes that more people will lead to more gene discoveries and that researchers will ultimately discover dozens of genes involved in this disorder. It is only one gene variant, she says. However, it may be the beginning block to building the information tower.

In people with other addictions, genes have been identified that relate to impulsivity, as well as their biological response to the drug. Demontis states that although it is not clear how CHRNA2 affects cannabis use risk, it has been shown that the gene can alter how someone reacts to the drug.

Demontis states that so far she's only been able to access genetic data from a very small subset of northern Europeans. In order to access the larger database of U.S. scientists, she has been collaborating. A larger database is more effective in finding risk genes, as well as genes that are connected to specific populations.

Joel Gelernter from Yale School of Medicine is also a professor of psychoiatry. Gelernter plans to examine his data for evidence of the gene.

Gelernter said, "It's very likely that [this discovery] adds something which's really of interest to our biological understanding of how cannabis dependence works and why certain people are more susceptible to becoming cannabis dependent than other people," but he was not part of this new study. It affects approximately 1-1.5 percent.

Researchers in Denmark also made sure that there was no false link between the disease and its gene. Researchers found that marijuana abuse was not linked to schizophrenia or cigarette smoking.

Gelernter said that past data showed that schizophrenia could increase the chance of getting cannabis use disorder. This suggests that certain genes might play an important role in either one. Gelernter says one reason for schizophrenia and cannabis use could be the shared genetic risk.

Also, the study found that cannabis abuse disorder is associated with lower educational attainment. It suggests that those who use cannabis may do worse in school. But this does not apply to all people who use marijuana.

Howard Edenberg is a Indiana University Distinguished Professor who did not participate in the research but specializes in genetics and substance abuse. Edenberg says that "we know we are missing a greater part of the picture." Edenberg says he expects that some genes will be found to contribute to the risk of several forms of abuse while others are unique to specific conditions like alcoholism or cannabis use disorder.

With other forms of substance abuse, he says, scientists are close to reaching an inflection point where enough genes have been identified to provide a new understanding of the biology and behavior of addiction. Although one gene identification isn't enough to make such an advancement, it is necessary.