LONDON (Agence de Presse Medicale for Reuters Health) - New evidence that some cannabis users may be genetically more vulnerable to schizophrenia is reported scientists in Britain, New Zealand and the United States.
The team, from King’s College London, the University of Otago and the University of Wisconsin followed a cohort of 1037 children through adulthood to find out why cannabis use was associated with emerging psychosis in a minority of users but not in others.
Their findings, published online in Biological Psychiatry, show that people with one version of the catechol-O-methyltransferase (COMT) gene were statistically more likely to develop a psychotic illness in their 20s -- but only if they were cannabis users during adolescence.
The COMT gene, which helps control dopamine, comes in two versions, valine and methionine. The study revealed that the valine version conferred vulnerability to cannabis-related psychosis.
In the full cohort of 26-year-olds, the base rate of psychotic conditions was 3%. Among the subset that used cannabis as teens, the rate of psychosis was 8%. However, among individuals with the COMT valine genotype who used cannabis as teens, the rate was 15%.
Avshalom Caspi and colleagues said the results “provide evidence that adolescent cannabis use, but not adult use, is associated with later psychosis outcomes. This suggests that the genetic-environmental interaction is limited to a sensitive period of brain development in adolescence.
“This study does not imply that cannabis is a major threat to public health,” they added in a statement. “Even if they had the risk genotype, 85% of young cannabis users did not develop psychosis.”
The researchers pointed out that 25% of people carry two copies of the valine version of the COMT gene, so it is too common to be a direct cause of disease.
MeSH Headings:Affective Disorders, PsychoticCopyright © 2002 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.
