Similar white matter aberrations in children with autism and their unaffected siblings: a diffusion tensor imaging study using tract-based spatial statistics.

CONTEXT Autism is a neurobiological condition with a strong genetic component. Recent diffusion tensor imaging (DTI) studies have indicated that white matter structure is aberrant in autism. To date, white matter structure has not been assessed in family members of children with autism. OBJECTIVE To determine whether white matter structure is aberrant in children with autism and their unaffected siblings compared with controls, and to test the hypothesis that white matter structure in autism is correlated with autism spectrum symptomatology. DESIGN Cross-sectional, case-control, voxel-based, whole-brain DTI analysis using Tract-Based Spatial Statistics. SETTING University research center. Patients  A sample of 37 children: 13 subjects with autism, 13 of their unaffected siblings, and 11 controls. Controls were age- and intelligence quotient-matched to the unaffected siblings; all groups were age matched. Main Outcome Measure  Fractional anisotropy (FA) and axial and radial diffusivities. In addition, behavioral correlation analyses were conducted using the Autism Diagnostic Interview and Autism Diagnostic Observation Schedule subscales and FA values, as well as axial diffusivity values in the autism group. RESULTS Compared with the control group, both the autism and sibling groups had widespread, significantly reduced white matter FA values (P ≤ .05, corrected) in the frontal parietal and temporal lobes and included, but were not restricted to, regions known to be important for social cognition. Within regions of reduced FA, significant reductions in axial diffusivity, but not radial diffusivity, were observed. There were no significant differences in white matter structure between the autism and sibling groups. There were no significant correlations between autism symptomatology and white matter FA or axial diffusivity. CONCLUSIONS Our findings suggest that white matter structure may represent a marker of genetic risk for autism or vulnerability to development of this disorder.