Distinct and shared intrinsic resting-state functional networks in children with idiopathic autism spectrum disorder and fragile X syndrome.

Autism spectrum disorder (ASD) and fragile X syndrome (FXS) are behaviorally overlapped. However, little is known about the functional patterns underlying the cognitive and behavioral characteristics of FXS and ASD. The present study aimed to identify the distinct or/and shared functional networks in young children with FXS and idiopathic ASD. We recruited 150 children consecutively in a group with FXS, a group with idiopathic ASD, and a group with typically developing (TD) children. Resting-state functional magnetic resonance imaging (fMRI) and behavioral data were collected and genetic information was obtained in the FXS group. We compared functional connectivity (FC) among the three groups and found that both FXS and ASD showed significantly decreased FC among the default mode network (DMN), sensorimotor network (SMN), cerebellum network (CN), and visual network (VN) relative to TD. FXS specifically demonstrated decreased FC within DMN, while both FXS and ASD exhibited significantly decreased FC within the CN and also between the CN and DMN, SMN, VN, respectively. Aberrant topological alterations of CN were identified in children with FXS and ASD, while ASD group showed significantly lower segregation in regions that integrate sensory and visual information, and motor coordination function. Moreover, correlations between the severity of social affect and mean FC of various cerebral-cerebellum networks in FXS exhibited significantly distinct trends from those observed in ASD. In the FXS group, the topological measure at crus I of the cerebellum is found to be negatively associated with DNA methylation levels. These results were statistically robust and demonstrated the shared and distinct profiles of intrinsic functional networks in FXS and ASD, two phenotypically overlapping developmental disorders.