Selective mutism in children with and without an autism spectrum disorder: The role of sensory avoidance in mediating symptoms of social anxietyDespite Selective Mutism (SM) and Autism Spectrum Disorder (ASD) often presenting together in clinical practice, there is no research to guide assessment processes (McKenna et al., 2017), with earlier editions of the DSM hindering professionals' readiness to diagnose ASD and SM together (Valaparla et al., 2018). While SM is currently characterised as an anxiety disorder in which individuals consistently fail to speak in specific social environments where it is expected, despite speaking in other situations, ASD is recognised by deficits in repetitive behaviours and social communication (APA, 2013). Children with ASD are vulnerable to developing SM due to their associated social anxiety (Settipani, et al., 2012;Sharkey & McNicholas, 2008), speech and language difficulties (Cohan et al., 2008;Müller et al., 2008), and sensory impairments, which can involve an under or over responsiveness to stimuli (Henkin & Bar-Haim, 2015). Therefore, this study aimed to explore the relationship between sensory behaviours and social anxiety in children with SM by comparing a group of children with SM both with, and without, an additional ASD diagnosis.SM is generally accepted as a behavioural response to anxiety (Young et al., 2012), where it is hypothesised that fear physically disables the throat or larynx (Ruiz & Klein, 2013;Sluckin & Smith, 2015). Consequently, SM's link with anxiety stems from its high co-occurrence with anxiety disorders in general (Cunningham, et al., 2006;Cunningham et al., 2004). Although individuals can outgrow SM, symptoms of co-occurring social anxiety disorder often persist (Sutton, 2013); it has been proposed that SM may either be a subtype of social anxiety (Sharkey & McNicholas, 2008;Steinhausen et al., 2006), a severe form of it (Scott & Beidel, 2011), a symptom of social anxiety disorder (Black & Uhde, 1995;Krysanski, 2003) or a developmental variant or pre-cursor to social anxiety disorder (Standart & Courteur, 2003). Yet, there are significant differences between SM and social anxiety disorder, where SM typically manifests 2 2 during early childhood (between 2 to 5 years old; Muris & Ollendick, 2015), compared to social anxiety disorder's later average age of onset of 13 years old (Leichsenring & Leweke, 2017); this makes the longitudinal course of SM less clear.Historical misunderstandings surrounding SM and ASD are evident, given it is now emerging that a high proportion of children with SM are recognised as showing ASD. For example, Kearney & Rede, (2021) found 68.5% of children with SM also presented with a developmental disorder with 46.3% presenting with both anxiety and developmental disorders, suggesting a strong relationship between a developmental delay, anxiety and SM. Additionally, when exploring the association with ASD within individuals identified with SM, a retrospective examination of Swedish medical records revealed that 63% had a form...