Autism, the prototypic pervasive developmental disorder (PDD), is usually apparent by 3 years of age. It is characterized by a triad of limited or absent verbal communication, a lack of reciprocal social interaction or responsiveness, and restricted, stereotypic, and ritualized patterns of interests and behavior (Bailey et al., 1996, pubmed:8655659; Risch et al., 1999, pubmed:10417292). 'Autism spectrum disorder,' sometimes referred to as ASD, is a broader phenotype encompassing the less severe disorders Asperger syndrome (MIM:608638) and pervasive developmental disorder, not otherwise specified (PDD-NOS). 'Broad autism phenotype' includes individuals with some symptoms of autism, but who do not meet the full criteria for autism or other disorders. Mental retardation coexists in approximately two-thirds of individuals with ASD, except for Asperger syndrome, in which mental retardation is conspicuously absent (Jones et al., 2008; pubmed:18698615). [from MIM:209850; 2017.03.18]

X-linked autism-2 (AUTSX2) is associated with mutation in the neuroligin-4X (NLGN4X) gene. [from MIM:300495; 2017.03.18]

Neuroligins function as ligands for the neurexins, which are cell-surface receptors. The Ca(2+)-dependent neurexin/neuroligin complex is present at synapses in the central nervous system, is required for efficient neurotransmission, and is involved in the formation of synaptic contacts (summary by Reissner et al., 2008; pubmed:18812509). [from MIM:600568; 2017.03.18]