Olfactory and Social Impairments in Children with Autism Spectrum Disorders, Sensory Processing Challenges, and Typical Development

Background:

Individuals with autism spectrum disorder (ASD) show atypical sensory processing within the olfactory system. Quantitative measures of olfaction, including detection threshold, identification, and discrimination, have yielded inconsistent results, yet there is mounting evidence that individuals with ASD perform more poorly than typically developing peers on these measures. In addition, the relationship between quantitative olfactory impairments and clinically assessed autism-related behaviors has not been studied, and may help to identify olfaction as a potential biomarker of ASD.

Objectives:

To assess olfactory performance in children with ASD, including smell detection thresholds and odor identification, to determine if olfactory measures can discriminate between ASD and an age and IQ matched clinical comparison group of children with sensory processing challenges (SPC), and to assess the relationship between olfactory performance and autism-related behaviors.

Methods:

14 children with high-functioning ASD (Age=10.36±1.68), 15 children with SPC (Age=10.25±1.62), and 14 typically developing children (TYP; Age=9.40±1.38) participated in this study. Two measures of olfactory processing were assessed. Odor detection threshold was measured using the phenyl ethyl alcohol version of the Sniffin’ Sticks task. Smell identification was measured using the University of Pennsylvania Smell Identification Test (UPSIT). Autism severity was assessed using Module 3 of the Autism Diagnostic Observation Schedule (ADOS-2).

Results:

Children with ASD (M_ASD=24.07, SD_ASD=5.82) had significantly lower UPSIT scores than TYP children (M_TYP= 30.86, SD_TYP=3.61; t(26)= -3.71, p<.001), but no differences on the UPSIT were detected between children with ASD and SPC (M_SPC=27.73, SD_SPC = 5.19; t(27)= -1.79, p=.086) nor between children with SPC and TYP children (t(28)= -0.96, p=0.343). No difference in Sniffin’ Sticks detection threshold was observed between the three groups (M_ASD=7.77, SD_ASD=4.13; M_SPC=8.15, SD_SPC=4.64; M_TYP=8.66, SD_TYP=4.09). UPSIT scores showed a negative correlation with ADOS 2 total score (r(41)= -0.48, p=0.001) and with the Social Affect domain of the ADOS 2 (r(41)= -0.49, p<.001) but no significant relationship was detected between UPSIT scores and the Restricted Repetitive Behavior domain of the ADOS 2 (r(41)= -0.27, p=0.084). Correlation analyses showed no significant relationships between Sniffin’ Sticks detection threshold and ADOS 2 scores.

Conclusions:

Children with ASD showed reduced odor identification compared to typically developing children; however, in this preliminary sample, the two groups had similar odor detection threshold levels. In comparison to children with SPC, children with ASD showed similar odor identification and detection threshold levels. This finding suggests that the olfactory impairments observed in ASD may be specific to higher order olfactory processing but not unique to ASD. Both autism severity and social impairments were negatively associated with odor identification. The orbital frontal cortex (OFC) mediates odor identification and has also been implicated in social impairments; thus, impaired performance on this odor identification measure may be an especially useful quantitative biomarker of OFC involvement in children with ASD. We aim to validate the current preliminary findings with a larger sample, as data collection for this project is ongoing.