Introduction: MRI Diffusion Tensor Imaging (DTI) is used to assess the microstructural integrity of white matter. Subjects with both idiopathic autism spectrum disorder (ASD) and syndromic autism, such as in tuberous sclerosis complex (TSC), have altered diffusion in white matter pathways, but no study has investigated if diffusion parameters are similar across syndromic and idiopathic ASD. We hypothesize that diffusion abnormalities are common in autism regardless of its etiology and will use a four-point comparison between subjects with idiopathic autism, TSC with ASD, TSC without ASD, and controls to determine if diffusion values in the corpus callosum (CC) are similar across subjects with ASD.

Methods: DTI was performed in four age-matched (2.7-18.9yo) groups: 14 with idiopathic ASD, 13 with TSC and ASD, 13 with TSC without ASD, and 12 controls.  Tractography of the CC was performed and fractional anisotropy (FA) and mean diffusivity (MD) were calculated for each subject.  To distinguish effects related to ASD from those related to TSC, a two-way analysis of covariance (ANCOVA) will be applied, using age as a covariate.

Results: It is expected that subjects with TSC and ASD will have statistically similar FA and MD values in the CC as subjects with idiopathic autism and that these values will differ from both TSC subjects without ASD and controls.

Discussion: The results of this study will better elucidate if microstructural changes measurable on MRI correlate with the autism phenotype regardless of etiology; such results would suggest DTI imaging could be a biomarker for ASD.