An exploration of the relationship between autism spectrum disorders, theory of mind and the serotonin transporter promoter length polymorphism

Master Thesis


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University of Cape Town

Autism Spectrum Disorder (ASD) is a highly heritable prevalent pervasive developmental disorder. All cases have deficits in social communication and interaction and in restricted and repetitive behaviours and interests. The mechanisms underlying different clinical presentations remain elusive. Deficits in Theory of Mind (ToM), the ability to understand that others have mental states independent of one's own, have been suggested as a possibly underlying the socia l deficits in ASD. The serotonin transporter promoter length polymorphism (5 - HTTLPR) has been implicated in ASD, and as serotonin is implicated in social functioning more generally, it is possible that 5 - HTTLPR could underlie social functioning in ASD. As such, ToM and 5 - HTTLPR have been implicated in ASD, and specifically as underlying the social deficits typical of this disorder. This protocol assessed core ASD symptoms (i.e. deficits in social communication and interaction, and impairment in restricted and repetitive behaviours and interests) in 69 children with ASD between the ages of 7 and 14 years. The Autism Social Skills Profile, Social Communication Questionnaire, and Repetitive Behavior Scale - Revised assessed these symptoms. 5 - HTTLPR genotypes were established for 55 of these children. ToM was comprehensively assessed in 57 of the children using the University of Cape Town Autism Research Group's Theory of Mind Battery. This protocol is the first is a series of studies assessing the biological bases for social deficits in ASD. One of the main aims was to pilot the use of ASD scales in a local sample. The preliminary analyses assessed the performance of these scales. This data was also used to assess whether the new DSM - 5's merging of social communication and social interaction into a single domain was supported. Study One then assessed for possible relationships between 5 - HTTLPR and cores ASD symptoms, and hypothesised that the 5 - HTTLPR genotype with the most reduced serotonergic transmission woul d relate to increased deficits in social communication and interaction. Study Two explored possible relationships between core ASD symptoms and ToM, and between 5 - HTTLPR and ToM. It was expected that impairment in social communication and interaction would correlation with reduced ToM ability, and that ToM would be most impaired in children with the genotype with the most reduced serotonergic transmission. Preliminary analyses found the scales did not perform well in a local sample. This was likely due to cultural, socio - economic, and educational factors. The bluntness of the scales 13 and broad nature of ASD characteristics likely also contributed. The DSM - 5's diagnostic criteria were supported. Study One and Study Two found no relationships between core ASD symptoms, ToM, and 5 - HTTLPR. Core ASD symptoms were assessed very broadly and it was not possible to establish clear phenotypes for the participants, which likely undermined analyses. At most this protocol showed that broad assessment of core ASD symptoms is not specific enough to reveal relationships to underlying mechanisms, and that ToM and 5 - HTTLPR are not implicated when board measures are used. We emphasise the need for better measures in ASD. We also believe the serotonin system needs to be investigated beyond 5 - HTTLPR in ASD

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