Selective Mutism in Unilingual Children, Multilingual Children, and Children with a Co-morbid Autism Spectrum Disorder: Differences and Common Risk Factors.
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Objective: To evaluate characteristics of unilingual children with selective mutism, multilingual children with selective mutism and children with a co-morbid autism spectrum disorder (ASD). This research study will provide a much needed insight into the different risk theories of SM. Method: Information derived from the clinical files of 139 children, with SM referred for diagnosis and treatment to the academic hospital in Utrecht (UMCU) between 1973 and 2011, was analysed. 56% (78/139) of the SM children was unilingual, 28% (39/139) was multilingual, and 15% (21/139) had a co morbid ASD. Results: The symptoms at school of unilingual children were significantly less severe when compared to the other groups. When unilingual and multilingual children were compared, the unilingual SM children appeared to experience more delays in the early development of language, whereas the multilingual SM children seemed to have a slightly (not significant) less extended vocabulary. The co-morbid ASD children showed significant language delays as well as a slightly (not significant) less extended vocabulary. The ASD group was found to be more anxious and showed more internalizing problems when compared to the other two groups. Compared to standardized scores, anxiety problems, multilingualism, gross motor and language developmental delays and a co-morbid ASD are found to be more present in our sample. Oppositional behavior is reported by parents in over half of the SM children. Teachers reported stubbornness in over a third of the SM children. Symptom severity, measured by the amount of situations the child refuses to speak in, is found to be the least at home. Conclusion: The ASD subgroup showed significantly more behavioral problems and a higher severity of SM symptoms compared to the other two groups. The multilingual subgroup only showed significantly more problems in language development and severity of the SM symptoms. Developmental delays (both in gross motor development and language development) could be a risk factor in developing SM. Anxiety problems, oppositional behavior, multilingualism, and ASD seem to be related to SM.