Neurexins and neuroligins are two distinct families of single-pass transmembrane 
proteins localized at pre- and postsynapses, respectively. They 
trans-synaptically interact with each other and induce synapse formation and 
maturation. Common variants and rare mutations, including copy number 
variations, short deletions, and single or small nucleotide changes in neurexin 
and neuroligin genes have been linked to the neurodevelopmental disorders, such 
as autism spectrum disorders (ASDs). In this review, we summarize the structure 
and basic synaptic function of neurexins and neuroligins, followed by behaviors 
and synaptic phenotypes of knock-in and knock-out mouse of these family genes. 
From the studies of these mice, it turns out that the effects of neurexins and 
neuroligins are amazingly neural circuit dependent, even within the same brain 
region. In addition, neurexins and neuroligins are commonly involved in the 
endocannabinoid signaling. These finding may provide not only insight into 
understanding the pathophysiology, but also the concept for strategy of 
therapeutic intervention for ASDs.