synapses so its role in these organisms is unclear. Homologues of α-neurexin have also been found in several invertebrate species including Drosophila, Caenorhabditis elegans, honeybees and Aplysia. In Drosophila melanogaster, NRXN genes (only one α-neurexin) are critical in the assembly of glutamatergic neuromuscular junctions but are much simpler. Their functional roles in insects are likely similar to those in vertebrates. Role in synaptic maturation Neurexin and neuroligin have been found to be active in synapse maturation and adaptation of synaptic strength. Studies in knockout mice show that the trans-synaptic binding team does not increase the number of synaptic sites, but rather increases the strength of the existing synapses. Deletion of the neurexin genes in the mice significantly impaired synaptic function, but did not alter synaptic structure. This is attributed to the impairment of specific voltage gated ion channels. While neuroligin and neurexin are not required for synaptic formation, they are essential components for proper function. Clinical importance and applications Recent studies link mutations in genes encoding neurexin and neuroligin to a spectrum of cognitive disorders, such as autism spectrum disorders (ASDs), schizophrenia, and mental retardation. Cognitive diseases remain difficult to understand, as they are characterized by subtle changes in a subgroup of synapses in a circuit rather than impairment of all systems in all circuits. Depending on the circuit, these subtle synapse changes may produce different neurological symptoms, leading to classification of different diseases. Counterarguments to the relationship between cognitive disorders and these mutations exist, prompting further investigation into the underlying mechanisms producing these cognitive disorders. Autism Autism is a neurodevelopmental disorder characterized by qualitative deficits in social behavior and communication, often including restricted, repetitive patterns of behavior. It includes a subset of three disorders: childhood disintegrative disorder (CDD), Asperger syndrome (AS), and pervasive developmental disorder – not otherwise specified (PDD-NOS). A small percentage of ASD patients present with single mutations in genes encoding neuroligin-neurexin cell adhesion molecules. Neurexin is crucial to synaptic function and connectivity, as highlighted in wide spectrum of neurodevelopmental phenotypes in individuals with neurexin deletions. This provides strong evidence that neurexin deletions result in increased risk of ASDs, and indicate synapse dysfunction as the possible site of autism origin. Dr. Steven Clapcote et al.'s α-neurexin II (Nrxn2α) KO mice experiments demonstrate a causal role for the loss of Nrxn2α in the genesis of autism-related behaviors in mice. Schizophrenia Schizophrenia is a debilitating neuropsychiatric illness with multiple