Reduced brain connectivity along the autism spectrum controlled for familial confounding by co-twin design.

Researchers studied brain connectivity in twins to understand autism better. They found that autistic individuals had reduced connections between certain brain areas. Those with clinical autism showed differences in areas related to basic visual processing, while those with more autistic traits had changes in areas important for recognizing faces and processing complex visual information. Using twins helped control for genetic and family factors that might influence results.

This study examined brain connectivity in 87 twin pairs (174 individuals, 24 with clinical autism) using diffusion tensor imaging and a co-twin design to control for genetic and environmental factors. Results showed reduced structural brain connectivity associated with both clinical autism and autistic traits. Twins with clinical autism had decreased brainstem-cuneus connectivity compared to their co-twins, potentially indicating altered low-level visual processing. Higher autistic traits were linked to reduced connectivity between the left hippocampus and left fusiform/parahippocampal areas, regions important for face processing and higher-order visual functions.

The co-twin design strengthened findings by controlling for shared genetic and environmental influences.

Findings suggest distinct connectivity patterns associated with clinical autism versus autistic traits, potentially informing understanding of visual processing differences. The co-twin design provides stronger evidence by controlling for familial factors, supporting neurobiological differences in autism spectrum conditions.

Sample size of 174 individuals is moderate but autism group (n=24) is relatively small. Cross-sectional design limits causal inferences. Limited to structural connectivity measures and may not capture functional connectivity patterns.

Previous studies on brain connectivity correlates of autism have often focused on selective connections and yielded inconsistent results. By applying global fiber tracking and utilizing a within-twin pair design, we aimed to contribute to a more unbiased picture of white matter connectivity in association with clinical autism and autistic traits. Eighty-seven twin pairs (n = 174; 55% monozygotic; 24 with clinical autism) underwent diffusion tensor imaging. Linear regressions assessed within-twin pair associations between structural brain connectivity of anatomically defined brain regions and both clinical autism and autistic traits.

These were explicitly adjusted for IQ, other neurodevelopmental/psychiatric conditions and multiple testing, and implicitly for biological sex, age, and all genetic and environmental factors shared by twins. Both clinical autism and autistic traits were associated with reductions in structural connectivity. Twins fulfilling diagnostic criteria for clinical autism had decreased brainstem-cuneus connectivity compared to their co-twins without clinical autism. Further, twins with higher autistic traits had decreased connectivity of the left hippocampus with the left fusiform and parahippocampal areas.

These associations were also significant in dizygotic twins alone. Reduced brainstem-cuneus connectivity might point towards alterations in low-level visual processing in clinical autism while higher autistic traits seemed to be more associated with reduced connectivity in networks involving the hippocampus and the fusiform gyrus, crucial especially for processing of faces and other (higher order) visual processing. The observed associations were likely influenced by both genes and environment.