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Researchers determine autism based on the smell reaction
As a result of impaired sensorimotor coordination, autistic children do not show the usual defense reaction when they perceive unpleasant smells. They continue to take a deep breath instead of reflexively slowing their breathing down, reports the Israeli research team led by Liron Rozenkrantz from the Weizmann Institute of Science in the journal "Current Biology". A simple smell test could make diagnosis of autism much easier in the future.
According to the researchers, the reaction to odors has emerged in the current studies as a relatively reliable indicator of autistic disorders. In their study, the scientists were able to use the smell reaction to determine with more than 80 percent certainty whether a child suffered from autism. In addition, the extent of the lack of a defense response was related to the severity of the disease. The more pronounced the autistic disorders, the longer the children breathed in the unpleasant smells. In practice, the test could significantly simplify the diagnosis of autism.
Odor test with rotten fish and spoiled milk
As part of their study, the Israeli researchers at the Weizmann Institute took a closer look at the smell of 18 healthy children and 18 autistic children. The average age of the test subjects was seven years. The scientists connected the children to a special device, in which different smells can be blown into the nose via two nasal cannulas, and nasal breathing can be measured at the same time. The children were then exposed to pleasant smells of roses and shampoo as well as unpleasant smells of sour milk and spoiled fish. An odor reaction is normal here, in which pleasant smells are inhaled deeply and unpleasant smells require a reflex-like reduction in the volume of breath. Within ten minutes, the children were confronted with 20 different smells (10 pleasant / 10 unpleasant), while the scientists observed how the tidal volume, the peak air flow rate, the air flow rate and the duration of the sniffing behaved.
Missing immune response in autistic children
The examination of the four parameters showed a significant interaction with the fragrance value (pleasant versus unpleasant) in the healthy test subjects, which is rated as a normal smell reaction, the researchers report. The children had shown a corresponding reaction to the odorant properties within 305 milliseconds. In contrast, no comparable reaction was found in the autistic children. They showed significantly less differences between the reaction to unpleasant and pleasant smells. Instead of immediately holding their breath in the smell of rotten fish, the autistic children took a deep breath. In addition, the researchers observed a connection between the extent of the lack of defense response and the severity of the autistic disorder. The longer the test subjects also inhaled the unpleasant smells normally, the greater the impairments in social communication. According to their own information, the researchers were unable to find any comparable connection in motor skills.
Test regardless of language ability
According to the scientists, the differences between the autistic children and the healthy children were so pronounced that based on the smell test alone, it was possible to determine with 81% certainty whether a child had autism. In their view, the diagnostic options could be significantly improved with the help of the test, especially since this is not influenced by the children's language skills. The scientists see the cause of the lack of smell reaction in autistic children in the "limited sensorimotor coordination." Controlling breathing in the case of unpleasant and pleasant smells is a highly complex procedure that is permanently impaired in the case of autistic disorders. In addition, the changed sense of smell in turn contributes to impaired social communication, according to the researchers' hypothesis. Therefore, the extent of the lack of smell reaction is "predictive for impaired social communication, but not for generalized motor impairments."
Smell tests could make autism diagnosis much easier
According to the researchers, the development of a corresponding smell test could significantly facilitate the diagnosis of autism in the future, but further examinations are first necessary to eliminate existing uncertainties. So far, for example, it remains unclear whether this indicator is specific for autism or also occurs in other developmental disorders. The sample in the current study was also too small to be able to make clear statements here. Last but not least, a number of technical problems would have to be solved before the test could be a useful tool in everyday clinical practice, write Liron Rozenkrantz and colleagues. In the end, however, autism can be diagnosed relatively reliably - even in young children - within around ten minutes. (fp)