Researchers at the Washington University in St. Louis (WUSTL) have found a surprising correlation between marijuana dependency and genes, as well as childhood sexual abuse. The reason why some child survivors of adversity go on to become marijuana-dependant while others are able to use the recreational drug without problems may be explained by genetic variations in the endocannabinoid system (ECS) in the brain.

A system of cannabinoid receptors located throughout the peripheral and central nervous systems of the mammalian brain comprises the ECS. It controls numerous physiological processes such as mood, sensation, memory and appetite as well as the psychoactive effects of cannabis.

Tetrahydrocannabinol (THC) is the primary psychoactive compound present in marijuana that affects numerous bodily and mental functions, owing to its close structural resemblance with endocannabinoids – the brain’s natural enzymes that control these functions. The enzymes produced in the ECS convey signals between individual cells in the body as well as between neurons.

Caitlin E. Carey, lead author on the study, said in a WUSTL press release, “In this study, we investigated whether variation in genes within the endocannabinoid system may be particularly important in setting the stage for cannabis dependence, especially in the context of childhood trauma.”

Genetic data from 1,558 marijuana users in Australia, who also reported childhood sexual abuse, was examined for the study. Variations in a single building block of DNA, called a nucleotide, are represented as Single Nucleotide Polymorphisms (SNPs). Associations between SNPs and marijuana dependence symptoms were examined. It was found that differences within a particular SNP called rs604300 were clearly associated with childhood sex abuse and cannabis dependence.

Ryan Bogdan, assistant professor of psychological and brain studies and a senior author on the study, said in the press release, “We have long known that childhood adversity, and in particular sexual abuse, is associated with the development of cannabis dependence. However, we understand very little about the individual difference factors that leave individuals vulnerable or resilient to these effects.”

The research, among the first to highlight genetic makeup as a factor controlling marijuana dependency in the context of child abuse, has been published in the Journal of Abnormal Psychology.

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