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]

This form of autism, designated AUTS17, is associated with heterozygous loss-of-function mutation in the SHANK2 gene; exhibits incomplete penetrance. [from MIM:613436; 2018.04.19]

Many to one: 3 human to 1 Drosophila. The human genes are SHANK1, SHANK2, and SHANK3.