08 07 2015
Early diagnosis of autism is important to maximise the benefit of interventions. A test that does not involve lengthy observations or language & communication assessment could be really useful in early and easy identification of autism. Autistic individuals have impairments in sensory motor coordination. Defects in Internal Action Models (IAM) are considered significant in this. The relationship between IAM and social communication is still unclear.
Sniff response is an IAM important in olfaction. Sniff response depends on large-scale connectivity between ventral temporal olfactory cortex where odor valence is processed. It also depends on cerebellar circuits where the response is likely actuated. It is interesting to note that ventral temporal and cerebellar substrates of olfaction are the key neural substrates specifically implicated in ASD.
Sniff response modulates the sniff magnitude automatically in relation to the odor valence. i.e. the automatic response is to take deep sniffs when exposed to nicer smells compared with bad ones. Would autistic children show a different pattern? Could this be useful in early detection?
Liron Rozenkrantz et al from Weizmann Institute in Israel measured the sniff response in autistic children. Children were exposed to different odours and their sniff response were recorded using olfactometer and a special nasal cannula that delivered odors and measured the airflow. 18 autistic children and matched controls participated in this study.The procedure was completed in 10 minutes.
Normal children altered their sniff response to account for odour properties. Autistic children did not show this ability to modulate sniff response.They also found that the differences in pleasant versus unpleasant sniff duration along with the sniff volume for unpleasant odours effectively distinguished TD from ASD children with 81% accuracy. Children with more severe autism showed more aberrant sniffing i.e. longer sniff duration for unpleasant odors.They also found that aberrant sniffing correlated with social impairment scores and not with motor impairments .
The study suggest that altered olfaction can be a novel early diagnostic test for Autism. Autistic children fail to modulate their sniff response according to the odour. It has the specific advantage that this test is non verbal and non task dependent .
Limitations: It needs to be seen whether the observed defects are specific for Autism or whether same defects are seen in other neuro developmental disorders.
Summary of the article
Rozenkrantz L, Zachor D, Heller I, Plotkin A, Weissbrod A, Snitz K, Secundo L, Sobel N. Curr Biol. 2015 Jul. in Press.