Objectives: This first aim of this study was to investigate volumetric brain differences in adults with ASD by exploring CT, SA and CV in isolation. Secondly, we aimed to examine the relationship between these volumetric measures (i.e. degree of spatial overlap) in order to elucidate their potential multi-factorial aetiology.
Methods: Structural MRI data was collected on 84 well-characterized adult males with ASD (right-handed, mean age = 26 yrs, mean FSIQ = 110), and 84 age/IQ matched healthy right-handed male controls. Subjects were recruited with the support of the MRC AIMS (Autism Imaging Multi-centre Study) program. All individuals with ASD were diagnosed using ADI-R, ADOS, and ICD-10 research criteria. For each participant, a set of three morphological parameters (CV, CT, SA) was obtained at each spatial location on the cortical surface (i.e. vertex) using FreeSurfer software (http://surfer.nmr.mgh.harvard.edu). Initially, a vertex-based approach employing the general linear model (GLM) was used to examine differences in individual volumetric measures between groups. Subsequently, we examined the degree of spatial overlap between maps representing significant differences for each morphometric feature.
Results: Overall, individuals with ASD had significantly larger values in all three parameters (CV, CT and SA). Furthermore, there was little spatial overlap between maps for CT and SA, suggesting an independent and region specific effect of CT and SA, particularly in frontotemporal regions. Overall, the map of CV was a linear combination between CT and SA, with region-specific parameter weights.
Conclusions: The data suggests that volumetric brain differences in adults with ASD are the result of region-dependent variations in two distinct volumetric measures, CT and SA. These two morphological parameters most likely have distinct genetic and neuropathological mechanisms and should therefore be explored independently. We suggest that the spatial pattern presented here may reflect the multifactorial aetiology of ASD, and that future research should include examination of both CT and SA to explore the specific genetic and neuropathological underpinnings of ASD.