The autism spectrum or autistic spectrum describes a range of conditions classified as neurodevelopmental disorders in the fifth revision of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders 5th edition (DSM-5). The DSM-5, published in 2013, redefined the autism spectrum to encompass the previous (DSM-IV-TR) diagnoses of autism, Asperger syndrome, pervasive developmental disorder not otherwise specified (PDD-NOS), and childhood disintegrative disorder.[1] These disorders are characterized by social deficits and communication difficulties, stereotyped or repetitive behaviors and interests, sensory issues, and in some cases, cognitive delays.

A revision to autism spectrum disorder (ASD) was proposed in the Diagnostic and Statistical Manual of Mental Disorders version 5 (DSM-5), released May 2013.[2] The new diagnosis encompasses previous diagnoses of autistic disorder, Asperger's disorder, childhood disintegrative disorder, and PDD-NOS. Rather than categorizing these diagnoses, the DSM-5 will adopt a dimensional approach to diagnosing disorders that fall underneath the autism spectrum umbrella. It is thought that individuals with ASDs are best represented as a single diagnostic category because they demonstrate similar types of symptoms and are better differentiated by clinical specifiers (i.e., dimensions of severity) and associated features (i.e., known genetic disorders, epilepsy and intellectual disability). An additional change to the DSM includes collapsing social and communication deficits into one domain. Thus, an individual with an ASD diagnosis will be described in terms of severity of social communication symptoms, severity of fixated or restricted behaviors or interests and associated features. The restriction of onset age has also been loosened from 3 years of age to "early developmental period", with a note that symptoms may manifest later when demands exceed capabilities.

Autism forms the core of the autism spectrum disorders. Asperger syndrome is closest to autism in signs and likely causes;[3] unlike autism, people with Asperger syndrome have no significant delay in language development.[4] PDD-NOS is diagnosed when the criteria are not met for a more specific disorder. Some sources also include Rett syndrome and childhood disintegrative disorder, which share several signs with autism but may have unrelated causes; other sources differentiate them from ASD, but group all of the above conditions into the pervasive developmental disorders.[3][5]

Autism, Asperger syndrome, and PDD-NOS are sometimes called the autistic disorders instead of ASD,[6] whereas autism itself is often called autistic disorder, childhood autism, or infantile autism.[7] Although the older term pervasive developmental disorder and the newer term autism spectrum disorder largely or entirely overlap,[5] the former was intended to describe a specific set of diagnostic labels, whereas the latter refers to a postulated spectrum disorder linking various conditions.[8] ASD, in turn, is a subset of the broader autism phenotype (BAP), which describes individuals who may not have ASD but do have autistic-like traits, such as avoiding eye contact.[7]

Under the DSM-5, autism is characterized by persistent deficits in social communication and interaction across multiple contexts, as well as restricted, repetitive patterns of behavior, interests, or activities. These deficits are present in early childhood, and lead to clinically significant functional impairment.[9] There is also a unique form of autism called autistic savantism, where a child can display outstanding skills in music, art, and numbers with no practice.[10]

Asperger syndrome was distinguished from autism in the DSM-IV by the lack of delay or deviance in early language development.[11] Additionally, individuals diagnosed with Asperger syndrome did not have significant cognitive delays.[12]PDD-NOS was considered "subthreshold autism" and "atypical autism" because it was often characterized by milder symptoms of autism or symptoms in only one domain (such as social difficulties).[13] In the DSM-5, both of these diagnoses have been subsumed into autism spectrum disorder.[9]

Although autism spectrum disorders are thought to follow two possible developmental courses, most parents report that symptom onset occurred within the first year of life.[14][15] One course of development follows a gradual course of onset in which parents report concerns in development over the first two years of life and diagnosis is made around 34 years of age. Some of the early signs of ASDs in this course include decreased looking at faces, failure to turn when name is called, failure to show interests by showing or pointing, and delayed pretend play.[16] A second course of development is characterized by normal or near-normal development followed by loss of skills or regression in the first 23 years. Regression may occur in a variety of domains, including communication, social, cognitive, and self-help skills; however, the most common regression is loss of language.[17][18] There continues to be a debate over the differential outcomes based on these two developmental courses. Some studies suggest that regression is associated with poorer outcomes and others report no differences between those with early gradual onset and those who experience a regression period.[19] Overall, the prognosis is poor for persons with classical (Kanner-type) autism with respect to academic achievement and poor to below-average for persons across the autism spectrum with respect to independent living abilities; in each case, a lack of early intervention exacerbates the odds against success.[19] However, many individuals show improvements as they grow older. The two best predictors of favorable outcome in autism are the absence of intellectual disability and the development of some communicative speech prior to five years of age.[medical citation needed] Overall, the literature stresses the importance of early intervention in achieving positive longitudinal outcomes.[20]

While a specific cause or specific causes of autism spectrum disorders has yet to be found, many risk factors have been identified in the research literature that may contribute to the development of an ASD. These risk factors include genetics, prenatal and perinatal factors, neuroanatomical abnormalities, and environmental factors. It is possible to identify general risk factors, but much more difficult to pinpoint specific factors. In the current state of knowledge, prediction can only be of a global nature and therefore requires the use of general markers.[21]

The results of family and twin studies suggest that genetic factors play a role in the etiology of autism and other pervasive developmental disorders.[22] Studies have consistently found that the prevalence of autism in siblings of autistic children is approximately 15 to 30 times greater than the rate in the general population.[23] In addition, research suggests that there is a much higher concordance rate among monozygotic twins compared to dizygotic twins.[24] It appears that there is no single gene that can account for autism. Instead, there seem to be multiple genes involved, each of which is a risk factor for part of the autism syndrome through various groups.[25][26][27]

A number of prenatal and perinatal complications have been reported as possible risk factors for autism. These risk factors include maternal gestational diabetes, maternal and paternal age over 30, bleeding after first trimester, use of prescription medication (e.g. valproate
) during pregnancy, and meconium in the amniotic fluid. While research is not conclusive on the relation of these factors to autism, each of these factors has been identified more frequently in autistic children compared to their non-autistic siblings and other normally developing youth.[30]

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