Genetic and Environmental Influences on Lobar Brain Structures in Twins With Autism

This investigation examined whether the variation of cerebral structure is associated with genetic or environmental factors in children with autism spectrum disorder (ASD) compared with typically developing (TD) controls. T-1-weighted magnetic resonance imaging scans were obtained from twin pairs (aged 6-15 years) in which at least one twin was diagnosed with ASD or both were TD. Good quality data were available from 30 ASD, 18 discordant, and 34 TD pairs (n = 164). Structural measures (volume, cortical thickness, and surface area) were generated with FreeSurfer, and ACE modeling was completed. Lobar structures were primarily genetically mediated in TD twins (a(2) = 0.60-0.89), except thickness of the temporal (a(2) = 0.33 [0.04, 0.63]) and occipital lobes (c(2) = 0.61 [0.45, 0.77]). Lobar structures were also predominantly genetically mediated in twins with ASD (a(2) = 0.70-1.00); however, thickness of the frontal (c(2) = 0.81 [0.71, 0.92]), temporal (c(2) = 0.77 [0.60, 0.93]), and parietal lobes (c(2) = 0.87 [0.77, 0.97]), and frontal gray matter (GM) volume (c(2) = 0.79 [0.63, 0.95]), were associated with environmental factors. Conversely, occipital thickness (a(2) = 0.93 [0.75, 1.11]) did not exhibit the environmental contributions that were found in controls. Differences in GM volume were associated with social communication impairments for the frontal (r = 0.52 [0.18, 0.75]), temporal (r = 0.61 [0.30, 0.80]), and parietal lobes (r = 0.53 [0.19, 0.76]). To our knowledge, this is the first investigation to suggest that environmental factors influence GM to a larger extent in children with ASD, especially in the frontal lobe.