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Autism spectrum disorders (ASDs) comprise a group of common neurodevelopmental disorders whose pathogenesis remains unclear. More than 100 genes have been associated with ASDs, some of which have shown to play important roles in the development and function of synapses, a crucial step of information transmission between neurons. Studies have found abnormalities in synaptic transmission, density, and structures in the brains of autistic patients. NRXN-NLGN-SHANK pathway has been associated with synaptic function of the brain, and its primary role is to regulate synaptic formation, elimination, plasticity and maturation. Genes including NRXN, NLGN, SHANK, and PSD95 are involved in the NRXN-NLGN-SHANK pathway. Mutations of such genes may lead to dysfunction of the pathway and ASDs-related phenotypes found in patients and animal models. This paper has provided a review for the research progress made on the mutations of NRXN-NLGN-SHANK pathway related genes and their roles in the pathogenesis of ASDs.

Objective: To conduct a follow-up investigation of structural changes of the corpus callosum fibers of toddlers (2 to 5 years of age) with autism spectrum disorder(ASD) and to explore the associations with clinical symptoms. Method: In this prospective randomized controlled study, ASD children who were diagnosed in the Child Mental Health Research Center, Nanjing Brain Hospital Affiliated to Nanjing Medical University from May 2011 to November 2012 were included in the ASD group, and developmentally delayed children were included in the control group (DD group). Diffusion tensor imaging (DTI) data from the two groups were obtained at two age levels: 2-3 years of age, and 4-5 years of age. Region of interest analysis was applied to assess characteristic values of total area and sub-regions of corpus callosum: the fraction anisotropy (FA), the mean diffusivity (MD), the radial diffusivity (RD) and the axial diffusivity (AD). All children were assessed using the Autism Diagnostic Interview-Revised (ADI-R) and Autism Treatment Evaluation Checklist (ATEC). The characteristic values of total area and sub-regions of corpus callosum of ASD group at two age levels were analyzed by paired sample t test; the characteristic values of total area and sub-regions of corpus callosum of ASD group and DD group were analyzed by independent-sample t test; the correlations between FA values of the total area and sub-regions of corpus callosum and ADI-R or ATEC scores were analyzed by Pearson correlation analysis. Result: Forty cases meeting inclusion criteria were enrolled in ASD group, and 31 eligible cases were enrolled in the control group. Four children in the ASD group were lost to follow-up, and 5 children in the control group were lost to follow-up. Longitudinal comparison between the two age subgroups of ASD patients showed that the FA values of the total corpus callosum increased (0.499 55±0.027 59 vs . 0.505 83±0.086 64, t= 4.88, P <0.05), but MD values, RD values and AD values of the total corpus callosum area decreased (0.000 89±0.000 03 vs . 0.000 81±0.000 14, 0.000 61±0.000 04 vs. 0.000 55±0.000 09, 0.001 43±0.000 03 vs . 0.001 38±0.000 03, t= 9.31, 7.90, 8.66, P <0.05 for all comparisons). In the area of corpus callosum genu, FA and AD values increased ( t= 5.59, 8.48, P <0.05 for both comparisons), but MD and RD values decreased ( t= 12.67, 11.28, P <0.05 for both comparisns). In the area of corpus callosum body, FA and RD values increased( t= 5.46, 8.48, P <0.05 for both comparisons), but MD and AD values decreased ( t= 8.08, 6.22, P <0.05 for both comparisons). In the area of corpus callosum splenium, MD, RD and AD values decreased ( t= 6.81, 4.44, 5.51, P < 0.05 for all comparisons). Among the participants 2 to 3 years of age, there were no significantly differences in FA values of total area and sub-regions of corpus callosum between ASD group and the DD group ( P > 0.05 for all comparisons); as compared with the DD group, ASD group had higher AD values of total area and splenium of corpus callosum (0.001 43±0.000 03 vs . 0.001 40±0.000 04, 0.001 34±0.000 03 vs . 0.001 32±0.000 04, t= 1.56, 1.14, P < 0.05 for both comparisons); ASD group had lower AD values but higher RD and MD values of corpus callosum genu ( t= 0.07, 0.55, 0.07, P < 0.05 for all comparisons); ASD group had lower RD values of corpus callosum body ( t= 0.07, P < 0.05). Among the participants 4 to 5 years of age, as compared with the DD group, ASD group had higher FA value of total corpus callosum area(0.505 83±0.086 64 vs . 0.483 77±0.099 30, t= 8.56, P < 0.05), lower RD value of total corpus callosum(0.000 55±0.000 09 vs . 0.000 56±0.000 12, t= 14.44, P < 0.05), lower RD values of corpus callosum body ( t= 2.20, P < 0.05), higher FA values ( t= 3.35, P < 0.05) but lower AD values of corpus callosum splenium ( t= 2.20, P < 0.05). A correlation analysis between FA values of total area and sub-regions of corpus callosum and clinical variables showed that the FA values of total area and splenium of corpus callosum in ASD group at 2 to 3 years of age were negatively correlated with the scores of language skills in ATEC ( r=- 0.35,-0.36, P < 0.05 for both comparisons). And after two years, FA values of total corpus callosum were positively correlated with the scores of social communication in ATEC ( r= 0.34, P < 0.05). There was no significant correlation between FA values of sub-regions of corpus callosum and the scores of ATEC ( P > 0.05 for all comparisons). There was no significant correlation between FA values of total area and sub-regions of corpus callosum and the scores of ADI-R ( P > 0.05 for all comparisons). Conclusion: The fiber structure of corpus callosum was still in the process of maturing during the age of 2 to 5 years; however, compared with DD group, ASD group had more extensive structural abnormalities of the corpus callosum fibers as age increased, and the structural abnormalities had correlation with the core symptoms of ASD. Trial registration Chinese Clinical Trial Registry, ChiCTR-OPC-17011995.