Dysfunction of brain-derived arginine-vasopressin (AVP) systems may be involved 
in the etiology of autism spectrum disorder (ASD). Certain regions such as the 
hypothalamus, amygdala, and hippocampus are known to contain either AVP neurons 
or terminals and may play an important role in regulating complex social 
behaviors. The present study was designed to investigate the concomitant changes 
in autistic behaviors, circulating AVP levels, and the structure and functional 
connectivity (FC) of specific brain regions in autistic children compared with 
typically developing children (TDC) aged from 3 to 5 years. The results showed: 
(1) children with ASD had a significantly increased volume in the left amygdala 
and left hippocampus, and a significantly decreased volume in the bilateral 
hypothalamus compared to TDC, and these were positively correlated with plasma 
AVP level. (2) Autistic children had a negative FC between the left amygdala and 
the bilateral supramarginal gyri compared to TDC. The degree of the negative FC 
between amygdala and supramarginal gyrus was associated with a higher score on 
the clinical autism behavior checklist. (3) The degree of negative FC between 
left amygdala and left supramarginal gyrus was associated with a lowering of the 
circulating AVP concentration in boys with ASD. (4) Autistic children showed a 
higher FC between left hippocampus and right subcortical area compared to TDC. 
(5) The circulating AVP was negatively correlated with the visual and listening 
response score of the childhood autism rating scale. These results strongly 
suggest that changes in structure and FC in brain regions containing AVP may be 
involved in the etiology of autism.