White matter microstructure in children with autistic traits.

Autism spectrum disorder (ASD) is thought to arise from aberrant development of connections in the brain. Previous studies have identified differences in white matter microstructure in children with ASD, offering support to such hypotheses. While ASD is thought to represent the severe end of a spectrum of traits, there are no studies evaluating white matter microstructure in relation to autistic traits in children from the general population. In a population-based sample of 604 6-to-10 year-old children, we assessed the relation between a continuous measure of autistic traits and white matter microstructure, using both probabilistic tractography and Tract-Based Spatial Statistics (TBSS). Using the TBSS approach, a cluster in the left superior longitudinal fasciculus (SLF) was identified where autistic traits negatively associated with fractional anisotropy (FA). In addition, two clusters of lower axial diffusion were identified; one in the corpus callosum and another in the corticospinal tract. Part of the findings remained when excluding children with ASD and were paralleled with similar, trend-level differences in 19 children with ASD, compared to matched controls. This study showed localized associations between autistic traits on a continuum and white matter microstructure, which could indicate a continuum of the neurobiology along the spectrum of autistic symptoms.