"This result provides genetic evidence that marijuana use can result in schizophrenia or a significantly increased risk of schizophrenia," lead researcher Hiroshi Ujike, a clinical psychiatrist at Okayama University, told United Press International.
Schizophrenia is one of the greatest mental health challenges in the world, affecting roughly one of every 100 people and filling about a quarter of all hospital beds in the United States. For years, clinical scientists have known that abusing marijuana, also known as cannabis, can trigger hallucinations and delusions similar to symptoms often found in schizophrenia. Prior studies also show that cannabis used before age 18 raises the risk of schizophrenia six-fold.
The hallucinogenic properties of marijuana, the researchers explained, are linked to a biochemical found abundantly in the brain. The chemical, called cannabinoid receptor protein, studs the surfaces of brain cells and latches onto the active chemical within marijuana known as THC.
"These sites are where marijuana acts on the brain," Ujike said.
Ujike and his team examined the gene for the marijuana receptor in 121 Japanese patients with schizophrenia and an average age of 44. When they compared this gene in schizophrenics with the same gene in 148 normal men and woman of the same average age, they found distinct abnormalities in DNA sequences called nucleotides among the schizophrenics. Some of their nucleotides in the marijuana receptor gene appeared significantly more often than normal while others appeared less frequency.
"This finding is the first to report a potential abnormality of the cannabinoid system in schizophrenia," said clinical neuroscientist Carol Tamminga at the University of Maryland in College Park. "The importance of a finding here cannot be overstated, in that it would form a tissue target for drug development and allow targeted treatments to emerge for the illness."
It appears malfunctions in the brain's marijuana-linked circuitry may make one vulnerable to schizophrenia, Ujike said. This holds especially true for a condition called hebephrenic schizophrenia, which is marked by deterioration of personality, senseless laughter, disorganized thought and lack of motivation. These symptoms are similar to psychotic behavior sometimes triggered by severe cannabis abuse, which could mean the marijuana receptors in schizophrenics are far more active than they should be.
Ujike stressed there is no evidence yet these genetic abnormalities can affect how the marijuana receptor actually acts in the brain. "We would also like to replicate our findings with different ethnic populations and more people," he added.
The researchers described their findings in the scientific journal Molecular Psychiatry.
(Reported by Charles Choi, UPI Science News, in New York)