Having Siblings is Associated with Better Social Functioning in Autism Spectrum Disorder Esther Ben-Itzchak 1,2 & Noa Nachshon 1 & Ditza A. Zachor 2,3 # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Sibling relationships play a unique developmental role, especially in emotional and social domains. In autism spectrum disorder (ASD), social-communication skills are often impaired in comparison to typical development. Therefore, studying siblings’ effects on social skills of the child with ASD is important. This retrospective study examined how autism severity and functioning were affected by having older and younger sibling/s, the sex of the index child and of the sibling, and the number of siblings. The study population included 150 participants with ASD (mean age = 4:0 ± 1:6), divided into three equal groups (no sibling, older and younger siblings), matched for cognitive level. The evaluation included neurological and standardized behavioral, cognitive, and functional assessments. Children with ASD with older siblings showed less severe social interaction deficits and better social adaptive skills than only children. No significant differences in autism severity and adaptive functioning were noted between the group with younger siblings and the other groups. The more older siblings the affected child had, the better their social functioning. The sex of the participants with ASD and that of the sibling were not associated with social functioning. Social interaction deficits, the presence of older or younger siblings for children with ASD, and higher cognitive ability contributed significantly to the explained variance (48.9%) in social adaptive skills. These findings emphasize that older siblings positively influence the social skills of their younger sibling with ASD. The effect of typically developing younger siblings was modest and seen only in children with ASD and better cognition. Keywords Autism spectrum disorder . Older sibling . Younger sibling . Adaptive skills . Autism severity Introduction Autism spectrum disorder (ASD) is a lifelong neurodevelopmental disorder characterized by impaired recip- rocal social communication and a pattern of restricted, often non-adaptive repetitive behaviors, interests and activities (APA 2013). As a spectrum disorder, the severity of ASD can vary considerably between individuals, impacting cogni- tive development, as well as social-communication, emotion- al, and adaptive behaviors (Zachor and Ben-Itzchak 2016). The social difficulties which are prevalent in children with ASD limit their opportunities to interact with peers. As such, family members play a critical role in the child’ s life, simply by being the most available people with whom the child can communicate (El-Ghoroury and Romanczyk 1999). In the general population, studies have found that sibling relation- ships play an important and unique role in typical develop- ment. The quantity and frequency of the interactions, stability and accessibility of the relationships between siblings, and the shared experiences and roles each sibling takes on all provide ample opportunity for children to develop emotional and so- cial skills (Buist et al. 2013; Cicirelli 1982) and social under- standing (Bowlby 1973; Bretherton 1985; Buist et al. 2013). The presence of an older sibling has been found to play a role in the development of the younger sibling’ s cognitive abilities, such as academic skills (Dai and Heckman 2013), language skills (Prime et al. 2014) and the development of theory of mind (ToM) (McAlister and Peterson 2013; Wright and Mahfoud 2012). In the population with developmental disabilities, most studies which examined sibling relationships among children with ASD or other developmental difficulties focused on the * Esther Ben-Itzchak benitze@ariel.ac.il 1 Bruckner Center for Research in Ausim, Department of Communication Disorders, Ariel University, 40700 Ariel, Israel 2 The Autism Center, Department of Pediatrics, Assaf Harofeh Medical Center, 70300 Zerifin, Israel 3 Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel Journal of Abnormal Child Psychology https://doi.org/10.1007/s10802-018-0473-z