For Teen Boys At High Risk For Schizophrenia, Using Marijuana May Affect Their Brain Development

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If you have a genetic predisposition for schizophrenia, you may want to reconsider using marijuana. Getty images/ Paul J. Richards

Cannabis use may alter brain development among young males who already have a genetic predisposition to schizophrenia, finds a new study published in JAMA Psychiatry.

For a while now, schizophrenia and cannabis use have been connected in some way, but researchers are still puzzled on how. Some believe that frequent cannabis use may trigger schizophrenic episodes, but the evidence supporting these claims is still contested. In another study from the UK, researchers found that those predisposed to schizophrenia were more likely to use cannabis, and more frequently, than those who did not possess the gene.

To further these studies along, researchers from the Baycrest Health Sciences’ Rotman Research Institute in Canada decided to examine how cannabis use could possibly affect brain development among adolescent boys with this presdisposition. According to Dr. Tomas Paus, senior author and chair of population neuroscience at Baycrest, schizophrenia begins five years earlier in men than it does in women, which is why this particular study focuses on young men. Those with a high genetic risk score for schizophrenia are more vulnerable to environmental influences that could change the course of development in the brain.

“When you have [a high risk score for schizophrenia], that makes your brain a little more vulnerable, and those [associated] genes have a lot to do with the development and communication in the brain,” he told Medical Daily. “And if you have that disadvantage and you combine it with early use of cannabis, will your brain mature differently during adolescence?”

Paus, along with postdoctoral fellow Dr. Leon French, analyzed three existing studies -- the Saguenay Youth Study in Quebec, the Avon Longitudinal Study of Parents and Children in the UK, and the IMAGEN Study in the UK, Germany and France -- which entailed 1,577 participants between the ages of 12 and 21, 57 percent of whom were male and 43 percent were female.These participants from the preexisting studies were asked to take a polygenic test, which evaluates their genetic risk of developing schizophrenia, as well as report their cannabis use. Then, in order to get a better look at their brain development, the former studies used brain scan imaging to detect any differences among the participants.

Overall, they found that young boys with a higher risk of schizophrenia and reported cannabis use had a thinner cortex than others involved in the study. Paus explained that a thicker cortex has a “more extensive apparatus” for receiving and processing information.

If a cortex is thicker, Paus added “it is less likely to make mistakes when reconstructing reality.” However, a thinner cortex may have difficulties reconstructing what is happening around it and in some cases, this may even lead to hallucinations.

That said, Paus was careful not to say that thinner cortexes meant these participants were experiencing (or would experience) any hallmark signs of schizophrenia.

“This is not a clinical application, it’s just telling us that something is going on in the brain,” he said. “If the illness runs in your family, discourage your kids from smoking pot when they are young.”

While this experiment does show that cannabis use can influence the brain’s development of schizophrenia, this does not predict the likelihood a young man will develop this mental illness in the future. Paus said  that, on a practical level, this research suggests that doctors should check in more frequently with young men they know have both a genetic predisposition and interest in smoking pot. As to establishing direct causality, Paus says there is still more research to be done.

Source: Paus T, French L, Matcheri K. Neurodevelopmental Trajectories, Disconnection and Schizophrenia Risk. JAMA Psychiatry. 2015.

Power R. et al. Genetic predisposition to schizophrenia associated with increased use of cannabis. Molecular Psychiatry. 2014.

This article previously stated that Dr. Paus and Dr. French “recruited 1,577 participants between the ages of 12 and 21, 57 percent of whom were male and 43 percent were female,” and then “used brain scan imaging to detect any differences among the participants,” when their study analyzed data from three existing studies – the Sanguenay Youth Study in Quebec, the Avon Longitudinal Study of Parents and Children in the UK, and the IMAGEN Study in the UK, Germany France and Ireland – to obtain this information. 

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