The heritability of autism is the proportion of differences in expression of autism that can be explained by genetic variation; if the heritability of a condition is high, then the condition is considered to be primarily genetic. Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether autism spectrum disorder (ASD) is explained more by multigene interactions or by rare mutations with major effects.
Neurexins (NRXN) are a family of presynaptic cell adhesion proteins that have roles in connecting neurons at the synapse. They are located mostly on the presynaptic membrane and contain a single transmembrane domain. The extracellular domain interacts with proteins in the synaptic cleft, most notably neuroligin, while the intracellular cytoplasmic portion interacts with proteins associated with exocytosis. Neurexin and neuroligin "shake hands," resulting in the connection between the two neurons and the production of a synapse. Neurexins mediate signaling across the synapse, and influence the properties of neural networks by synapse specificity. Neurexins were discovered as receptors for α-latrotoxin, a vertebrate-specific toxin in black widow spider venom that binds to presynaptic receptors and induces massive neurotransmitter release. In humans, alterations in genes encoding neurexins are implicated in autism and other cognitive diseases, such as Tourette syndrome and schizophrenia.
LRRTM1 is a brain-expressed imprinted gene that encodes a leucine-rich repeat transmembrane protein that interacts with neurexins and neuroligins to modulate synaptic cell adhesion in neurons. As the name implies, its protein product is a transmembrane protein that contains many leucine rich repeats. It is expressed during the development of specific forebrain structures and shows a variable pattern of maternal downregulation.
PSD-95 also known as SAP-90 is a protein that in humans is encoded by the DLG4 gene.
Disks large homolog 3 (DLG3) also known as neuroendocrine-DLG or synapse-associated protein 102 (SAP-102) is a protein that in humans is encoded by the DLG3 gene. DLG3 is a member of the membrane-associated guanylate kinase (MAGUK) superfamily of proteins.
Disks large homolog 2 (DLG2) also known as channel-associated protein of synapse-110 (chapsyn-110) or postsynaptic density protein 93 (PSD-93) is a protein that in humans is encoded by the DLG2 gene.
Glutamate [NMDA] receptor subunit epsilon-1 is a protein that in humans is encoded by the GRIN2A gene. The canonical GluN2A subunit isoform encompasses 1464 amino acids. Alternative splicing can generate a primate-specific GluN2A-short isoform.
Kalirin, also known as Huntingtin-associated protein-interacting protein (HAPIP), protein duo (DUO), or serine/threonine-protein kinase with Dbl- and pleckstrin homology domain, is a protein that in humans is encoded by the KALRN gene. Kalirin was first identified in 1997 as a protein interacting with huntingtin-associated protein 1. Is also known to play an important role in nerve growth and axonal development.
Neurexin-1-alpha is a protein that in humans is encoded by the NRXN1 gene.
SH3 and multiple ankyrin repeat domains protein 2 is a protein that in humans is encoded by the SHANK2 gene. Two alternative splice variants, encoding distinct isoforms, are reported. Additional splice variants exist but their full-length nature has not been determined.
Synaptic Ras GTPase-activating protein 1, also known as synaptic Ras-GAP 1 or SYNGAP1, is a protein that in humans is encoded by the SYNGAP1 gene. SYNGAP1 is a ras GTPase-activating protein that is critical for the development of cognition and proper synapse function. Mutations in humans can cause intellectual disability, epilepsy, autism and sensory processing deficits.
Neuroligin-3 is a protein that in humans is encoded by the NLGN3 gene.
Neuroligin-1 is a protein that in humans is encoded by the NLGN1 gene.
Disks large-associated protein 2 is a protein that in humans is encoded by the DLGAP2 gene.
Neuroligin-2 is a protein that in humans is encoded by the NLGN2 gene.
SH3 and multiple ankyrin repeat domains 3 (Shank3), also known as proline-rich synapse-associated protein 2 (ProSAP2), is a protein that in humans is encoded by the SHANK3 gene on chromosome 22. Additional isoforms have been described for this gene but they have not yet been experimentally verified.
Neuroligin (NLGN), a type I membrane protein, is a cell adhesion protein on the postsynaptic membrane that mediates the formation and maintenance of synapses between neurons. Neuroligins act as ligands for β-Neurexins, which are cell adhesion proteins located presynaptically. Neuroligin and β-neurexin "shake hands", resulting in the connection between two neurons and the production of a synapse. Neuroligins also affect the properties of neural networks by specifying synaptic functions, and they mediate signalling by recruiting and stabilizing key synaptic components. Neuroligins interact with other postsynaptic proteins to localize neurotransmitter receptors and channels in the postsynaptic density as the cell matures. Additionally, neuroligins are expressed in human peripheral tissues and have been found to play a role in angiogenesis. In humans, alterations in genes encoding neuroligins are implicated in autism and other cognitive disorders.
Synapsin II is the collective name for synapsin IIa and synapsin IIb, two nearly identical phosphoproteins in the synapsin family that in humans are encoded by the SYN2 gene. Synapsins associate as endogenous substrates to the surface of synaptic vesicles and act as key modulators in neurotransmitter release across the presynaptic membrane of axonal neurons in the nervous system.
Chordin-like 1 is a protein that in humans is encoded by the CHRDL1 gene. Chordin-Like 1 (CHRDL1) is a structural glycoprotein that sits on the X chromosome and specifically encodes Venotropin, which is an antagonistic protein to bone morphogenic protein 4.
Synaptic stabilization is crucial in the developing and adult nervous systems and is considered a result of the late phase of long-term potentiation (LTP). The mechanism involves strengthening and maintaining active synapses through increased expression of cytoskeletal and extracellular matrix elements and postsynaptic scaffold proteins, while pruning less active ones. For example, cell adhesion molecules (CAMs) play a large role in synaptic maintenance and stabilization. Gerald Edelman discovered CAMs and studied their function during development, which showed CAMs are required for cell migration and the formation of the entire nervous system. In the adult nervous system, CAMs play an integral role in synaptic plasticity relating to learning and memory.
