How cannabis can trigger schizophrenia
Smoking cannabis affects brain chemistry so seriously it can trigger schizophrenia, scientists warn today.
Researchers have found the first evidence that marijuana can cause genetic abnormalities associated with the mental illness, which affects about one in every 100 people.
Many scientists have been warning for years that cannabis can trigger hallucinations and delusions similar to symptoms found in schizophrenia.
Previous studies have suggested that using the drug before the age of 18 raises the risk of the condition in later life by six-fold.
Its ability to cause psychotic conditions is probably related to long-term changes in the brain caused by a substance found in marijuana called tetrahydrocannabinol (THC).
THC affects chemicals in the brain that transmit information from one nerve cell to another.
Disrupting the delicate chemical balance can result in memory loss, anxiety and other conditions.
Rare genetic changes associated with a heightened risk of schizophrenia have been revealed by two independent studies.
The surveys have identified sections of the human genome that, when deleted, can elevate the risk of developing schizophrenia by up to 15 times compared with the general population.
Schizophrenia is a serious mental health problem and affects around 1 in every 100 people at some point during their lives. Genetic factors are thought to account for more than 70% of cases. But unlike many diseases with a genetic basis - and in common with many other psychiatric disorders - researchers have struggled to locate genes linked to the occurrence of the disease.
The new findings come from two large-scale studies done by multi-national collaborations, both of which are published in Nature this week. The first study comes from the International Schizophrenia Consortium (ISC), a collaboration of researchers from 12 institutions in Europe, the United States and Australia; the second comes from the SGENE consortium, made up of 18 institutions across Europe, the United States and China.
The new Japanese research was led by clinical psychiatrist Dr Hiroshi Ujike of Okayama University and reported in the journal Molecular Psychiatry.
The team examined the gene-controlling ‘receptors’ in the brain that respond to marijuana in 121 Japanese schizophrenics and a similar number of healthy men and women. ‘These sites are where marijuana acts on the brain,’ said Dr Ujike.
The scientists found distinct abnormalities in DNA among the schizophrenics.
Although these deletions do not offer a complete explanation of the genetic basis of schizophrenia, the replication of the findings between the two studies is important. “The fact that there are two independent studies that come at the problem from different angles and using different methodologies is fantastic for psychiatric genetics,” says Pamela Sklar of Harvard Medical School in Cambridge, Massachusetts, part of the ISC study.
Jonathan Flint, who studies the genetic basis of psychiatric diseases at the Wellcome Trust Centre for Human Genetics at the University of Oxford, UK, agrees that the results are a major advance, but points out that converting this association into a better understanding of the biology of schizophrenia is far from trivial. The genetic changes on chromosome 22 have been known for some time, he says, but the exact genes that cause the increase in risk still remain unclear.
Nevertheless, these are the first deletions associated with schizophrenia to be identified in such a large sample and across several populations, Stefánsson adds. “Schizophrenia is a disorder affecting thoughts and emotions. It is therefore a quintessentially human disease, but one that is little understood biologically and which is difficult to diagnose. These findings are important because they shed light on its causes and provide a first component to a molecular test to aid in clinical diagnosis and intervention.”
“It is very important to find out who is at risk [of schizophrenia] so they can avoid triggers such as cannabis,” says Marjorie Wallace, chief executive of the UK mental-health charity SANE. “But over the years we have seen many false positives in the search for the gene or genes, and we would therefore treat these findings with some caution. Although encouraging, they are a long way from finding the causes, treatment and, above all, much needed prevention of psychotic illness.”
Malfunctions in the brain’s marijuana-linked circuitry may make people vulnerable to schizophrenia, and smoking the drug might trigger the condition.
Another recent study suggested that using cannabis can damage everyday memory - such as putting names to faces or remembering to pick up car keys.
People who smoke the drug between five and 20 times a month have 10 per cent more of such memory problems than non-users. And those who smoke it more than 20 times a month have been found to be 20 per cent more deficient.
Despite the concerns, cannabis looks set to be downgraded in Britain from a class B to a class C drug.
The change means that traffickers will face a maximum of five years in jail, less than half the present 14-year term.
Home Secretary David Blunkett wants to soften the law on cannabis despite warnings that it can act as a gateway to hard drugs.
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by JAMES CHAPMAN, Daily Mail