Olfactory function assessment in Italian subjects with autism spectrum disorder

Introduction: The olfactory system is associated with several brain areas that might be involved in neurodegenerative processes and neurodevelopmental disorders. For this reason, investigation of the olfactory function plays an important role in the assessment of individuals with autism spectrum disorder (ASD), a neurodevelopmental disorder characterized by an impairment in social communication and by a restricted and repetitive pattern of behaviors. The aim of this study was to examine odor detection threshold, discrimination, and identification in participants with ASD compared to typically developing (TD) controls. Methods: Thirty Italian subjects (15 with ASD, mean age 19 ± 0.5 years, and 15 TD controls, mean age 21.7 ± 0.4 years) were evaluated by means of the Sniffin’ Sticks extended test through three different parameters, odor detection threshold, discrimination, and identification, and their sum the threshold, discrimination, and identification (TDI) score. Results: Our results indicated that the participants with ASD showed an impairment in odor detection threshold and TDI score compared to TD controls. No differences were found in odor identification and discrimination. Participants with ASD were significantly poorer in correctly identifying the following odors: leather, apple, rose, cinnamon, garlic, cloves, and anis. However, they were significantly better than TD controls in correctly identifying the odor of the following fruits: orange, banana, and lemon. Conclusion and Implications: Our data provide a comprehensive evaluation of the three olfactory components in an Italian population and confirm an impaired odor detection threshold and TDI score in subjects with ASD compared to TD controls. In conclusion, these results suggest that the Sniffin’ Sticks extended test might be a valid tool in early detection and differential diagnosis of neurodevelopmental disorders.