The genetic marker in question is one variation of a gene call AKT1. The new finding confirms earlier research, which also linked this marker with the risk of psychosis after smoking pot.

The AKT1 gene is known to be involved in the signaling of the brain chemical dopamine, which is abnormal in those with psychosis, Di Forti said.

The genetic marker likely acts along with other genes to contribute to the risk of psychosis from cannabis smoking, the researchers said. Finding the genetic underpinnings of cannabis psychosis may lead to the development of therapies for the condition, said Dr. John Krystal, editor of Biological Psychiatry, the journal in which the study was published Nov. 15.