Longitudinal DTI of the Corpus Callosum in Individuals with Autism Spectrum Disorder: Differences in Fractional Anisotropy

Thursday, May 17, 2012
Sheraton Hall (Sheraton Centre Toronto)
10:00 AM
A. Alexander1, B. G. Travers2, N. Adluru3, N. Lange4, C. Ennis5, P. T. Fletcher6, M. B. DuBray7, A. Froehlich8 and J. E. Lainhart9, (1)Psychiatry, University of Wisconsin, Madison, WI, (2)Waisman Center, University of Wisconsin-Madison, Madison, WI, (3)Waisman Center, University of Wisconsin, Madison, WI, (4)Psychiatry, Harvard University, Cambridge, MA, (5)University of Wisconsin, Madison, WI, (6)School of Computing, University of Utah, SLC, UT, (7)Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, UT, (8)University of Utah, Salt Lake City, UT, (9)Psychiatry, University of Utah, Salt Lake City, UT
Background: The corpus callosum is a white matter structure that enables efficient communication between the left and right hemispheres of the brain. Fractional anisotropy (FA) is a measure obtained through diffusion tensor imaging that is thought to indicate the fiber coherence of white matter tracts. Multiple cross-sectional studies have found evidence for decreased FA in the corpus callosum in persons with ASD (Alexander et al., 2007; Jou et al., 2011; Kumar et al., 2010; Shukla et al., 2010; 2011). However, to our knowledge, no study has longitudinally investigated FA of the corpus callosum in persons with ASD compared to typically developing controls (TDC). 

Objectives: The present study longitudinally investigated FA of the corpus callosum in persons with ASD compared to TDC’s. We predicted that individuals with ASD would show decreased FA across the corpus callosum.  Additionally, we predicted that symptoms of ASD may relate to corpus callosum FA.

Methods: Participants received DTI scans at three time-points across a 5-year period of time (DW, single-shot, spin-echo EPI, b=1000, 12 non-collinear directions, 4 averages). Forty-seven TDC’s and 100 individuals with ASD were scanned during at least one time point (most being scanned at all three time points).  Diagnostic groups were matched on age (TDC: 17.60±9.15; ASD: 17.58±6.85, range:  3.39-47.12 years, p = .99). The Social Responsiveness Scale (SRS) was administered to the majority of participants at both Time 1 and 2.

Results: We conducted a linear mixed effects model using a restricted maximum likelihood fit. Mean FA of the corpus callosum was modeled as a function of participant’s age, diagnosis, and corpus callosum size (covariate), keeping participant as a random-effects variable.  There was not a significant effect for age, but there was a significant group difference in FA (p < .001), such that the group with ASD appeared to have lower mean FA of the corpus callosum compared to TDC’s above and beyond the effect of corpus callosum size.  Correlations between mean FA of the corpus callosum and SRS Time 1 and Time 2 scores within the ASD group were not significant (p>.20), but became significant with the addition of the TDC group. 

Conclusions: Consistent with the findings of prior cross-sectional investigations, the present longitudinal results found that individuals with ASD have decreased FA in the corpus callosum white matter tracts compared to individuals with typical development. This decrease in FA may be indicative of less white matter fiber coherence in person with ASD. Contrary to our hypotheses, ASD symptom severity (as measured by the SRS) was not related to corpus callosum FA in the ASD group, although this relation did become significant with the addition of the group with typical development. Future analyses will be conducted to examine other measures of white matter integrity in this longitudinal dataset, such as mean diffusivity, axial diffusivity, and radial diffusivity.