Simple smell tests could help doctors identify people at risk of developing schizophrenia, a study suggests.
Doctors believe the test could be useful
It has long been known that people with schizophrenia or psychosis are unable to correctly identify smells.
But until now scientists were unsure whether this occurred before or after symptoms developed.
This latest study, published in the American Journal of Psychiatry, suggests it happens before the first symptoms appear.
High risk patients
Dr Warrick Brewer and colleagues at the University of Melbourne examined a group of people, all of whom were deemed to have a very high risk of developing psychosis.
They found those who went on to develop schizophrenia, rather than other forms of psychosis, were all unable to identify smells properly.
For instance, they thought the smell from a pizza actually came from an orange or the smell of bubblegum was actually smoke.
This problem was present before the onset of any significant clinical symptoms of psychosis.
The researchers believe their findings could lead to a new test for schizophrenia, which could in turn transform the way people with the condition are treated.
"An accurate and reliable diagnostic tool for schizophrenia could allow for early treatment or prevention and minimise the extensive and significant distress to those in the community directly and indirectly affected," said Dr Brewer.
The researchers believe that changes in the brain in the very early stages of schizophrenia may prevent people from identifying smells properly.
"It is the only sense that passes straight to this area of the brain," said Dr Brewer.
"Any vulnerability involving these neural circuits can affect our labelling of smell."
Professor Philip McGuire of the Institute of Psychiatry in London said the findings were promising.
"It sounds like a strange idea but it makes sense," he told BBC News Online.
"The part of the brain that perceives smells connects parts of the brain implicated in schizophrenia.
"If we were able to use a simple test of how we smell things to identify those at super risk of developing schizophrenia, that would be quite useful.
"Other people are trying to identify other biomarkers with brain scans, for instance. But these are quite expensive.
"Being able to do it in just a few minutes with a simple test is potentially very useful."
He said further studies are needed before doctors could adopt the technique.