A gene is a sequence of nucleotides contained in our DNA and RNA which carry the blueprints for the creation of different proteins. In the largest study of its kind, a genetic marker for cannabis use disorder (CUD) has been discovered by Danish researchers.

In a gene-wide association study, the researchers identified a gene that has been implicated with the control of the proliferation of a brain cell receptor which also binds to nicotine.

A gene-wide association study is an analysis of the genetic database on a certain population of animals for the purposes of determining which genes appear more often in animals carrying a certain biological trait, such as obesity or nicotine dependency.

In this case, Ditte Demontis and colleagues used a nationwide Danish cohort to analyze the genomes of more than 2,000 individuals with CUD and the genomes of nearly 50,000 control individuals to establish links between common genetic variants and CUD.

They found that the disorder was associated with a genetic variant that controls the expression of CHRNA2, a gene encoding a brain receptor for the neurotransmitter acetylcholine, which also binds to nicotine.

First of its Kind

According to the corresponding study published in Nature Neuroscience last week, “cannabis is the most frequently used illicit psychoactive substance worldwide, and around one in ten users become dependent”.

“As with other forms of addiction, cannabis use disorder (CUD) develops by frequent and harmful use of cannabis and involves engaging less in personal relationships and pleasurable activities, and experiencing cravings and withdrawal symptoms when the drug is not taken,” writes the authors.

Cannabis is still illegal under federal law in most nations across the world, but this is slowly beginning to change, particularly in the west, with Colorado, Michigan, Oregon, Maine, Washington, Alaska, and California all legalizing the plant for both medicinal and recreational purposes.

Nevada, Vermont and Massachusetts have also decriminalized cannabis, while several countries in Europe have also lifted restrictions.

In a meta-analysis published in Addiction in 2012 that consisted of 28 studies examining the results of clinical diagnoses, psychosocial problems and other outcomes associated with co‐occurring cannabis and tobacco use, the researchers found that cannabis users who also smoke tobacco were more dependent on cannabis, had more psychosocial problems, and a poorer chance to quit either substance.

In the Danish study, Demontis et al. went through the trouble of replicating their study in another Nordic population cohort, but this time much larger. 5,500 individuals with CUD and more than 300,000 control individuals from an Icelandic genetics cohort were examined with the same outcome appearing as in the smaller, Danish cohort.

In summary, these studies would suggest that cannabis-use dependency is exacerbated by the addition of tobacco, and that both substances are taken up by the same neuro-receptor. Even though this was the largest and most successful attempt at identifying the genetics behind CUD, the authors admit that further research is needed to understand the biological mechanisms by which these genetic differences contribute to the development of the disorder, and how this information could be used to improve treatment.

In the meanwhile, it would seem that if you’re trying to quit smoking, cannabis use should also be avoided as nicotine addiction looks very much like CUD and CUD looks very much like nicotine addiction.

Photo credit: Petr Brož GNU License