Smoking should be considered an "important" risk factor for schizophrenia, a scientist has claimed.
Professor Boris Quednow, from the University Hospital of Psychiatry in Switzerland, led new research suggesting smoking increases the impact of schizophrenia genes.
Healthy smokers carrying the gene variants responded to an "acoustic stimuli" test in the same way as individuals suffering from the serious mental disorder.
The effect also appeared to be stronger the more a person smoked.
The study involved more than 1,800 participants who underwent a simple test which involves listening to a sequence of similar clicks.
Brainwave measurements show that most people suppress other, irrelevant, stimuli while processing the sounds.
However patients with schizophrenia appear to lack this filtering mechanism. As a result their brains are thought to be inundated with too much information.
Psychiatrically healthy people carrying variants of the gene TCF4 that increased the risk of schizophrenia also displayed poorer acoustic filtering, the study found. However, smoking appeared to amplify the effect, resulting in greater deficits.
The findings are published today in the journal Proceedings of the National Academy of Sciences.
Prof Quednow said: "Smoking alters the impact of the TCF4 gene on acoustic stimulus filtering. Therefore, smoking might also increase the impact of particular genes on the risk of schizophrenia.
"Smoking should... be considered as an important cofactor for the risk of schizophrenia in future studies."
People with schizophrenia frequently smoke, the researchers pointed out.
A combination of the click test and genetic and smoking data could be used to diagnose schizophrenia more rapidly and define new patient sub-groups, said Dr Quednow.
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