Autism spectrum disorders (ASDs) are characterized by language impairments, social deficits, and repetitive behaviors. The onset of symptoms occurs by the age of 3 and shows a lifelong persistence. Genetics plays a major role in the etiology of ASD. Except genetics, several potential risk factors (environmental factors and epigenetics) may contribute to ASD. Copy number variations (CNVs) are the most widespread structural variations in the human genome. These variations can alter the genome structure either by deletion or by duplication. CNVs can be de novo or inherited. Chromosomal rearrangements have been detected in 5–10% of the patients with ASD and recently copy number changes ranging from a few kilobases (kb) to several megabases (Mb) in size have been reported. Recent data have also revealed that submicroscopic CNVs can have a role in ASD, and de novo CNVs seem to be a more common risk factor in sporadic compared with inherited forms of ASD. CNVs are being implicated as a contributor to the pathophysiology of complex neurodevelopmental disorders and they can affect a wide range of human phenotypes including mental retardation (MR), autism, neuropsychiatric disorders, and susceptibility to other complex traits such as HIV, Crohn’s disease, and psoriasis. This review emphasizes the major CNVs reported to date in ASD. 1. Introduction to Autism Spectrum Disorders Autism spectrum disorders (ASDs) include Asperger syndrome, autism, pervasive developmental disorder not otherwise specified, and childhood disintegrative disorder according to Diagnostic and Statistical Manual of Mental Disorders V (DSM-V) criteria [1–3]. ASDs, also termed as pervasive developmental disorders (PDDs), are characterized by impairments in reciprocal social interaction and communication with the presence of restricted and repetitive behaviors [4–8]. Many children with autism spectrum disorders also have intellectual disability, and most of them have lifelong disability requiring substantial social and educational support [5]. Autism was firstly described by Kanner in 1968 as a childhood developmental disorder [9]. Although ASDs are known to be highly heritable (90%), the underlying genetic mechanisms are still largely unknown and ASD affects ~1% of the population [10–14]. Unfortunately ASD is the most heritable disorder but is not a simple disorder and has a complex etiology [8, 15]. The genetic architecture of ASD comprises a diversity of rare single nucleotide variants, copy number variations (CNVs), chromosomal abnormalities, and common polymorphic variations. Candidate
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