Diagnosis is based on behavior, not cause or mechanism. Under the DSM-5,<unk>  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, typically before age three, and lead to clinically significant functional impairment. Sample symptoms include lack of social or emotional reciprocity, stereotyped and repetitive use of language or idiosyncratic language, and persistent preoccupation with unusual objects. The disturbance must not be better accounted for by Rett syndrome, intellectual disability or global developmental delay. ICD-10 uses essentially the same definition. Several diagnostic instruments are available. Two are commonly used in<unk>  research: the<unk>  Diagnostic Interview-Revised (ADI-R) is a semistructured parent interview, and the<unk>  Diagnostic Observation Schedule (ADOS) uses observation and interaction with the child. The Childhood<unk>  Rating Scale (CARS) is used widely in clinical environments to assess severity of<unk>  based on observation of children. The Diagnostic interview for social and communication disorders (DISCO) may also be used. A pediatrician commonly performs a preliminary investigation by taking developmental history and physically examining the child. If warranted, diagnosis and evaluations are conducted with help from ASD specialists, observing and assessing cognitive, communication, family, and other factors using standardized tools, and taking into account any associated medical conditions. A pediatric neuropsychologist is often asked to assess behavior and cognitive skills, both to aid diagnosis and to help recommend educational interventions. A differential diagnosis for ASD at this stage might also consider intellectual disability, hearing impairment, and a specific language impairment such as Landau–Kleffner syndrome. The presence of<unk>  can make it harder to diagnose coexisting psychiatric disorders such as depression. Clinical genetics evaluations are often done once ASD is diagnosed, particularly when other symptoms already suggest a genetic cause. Although genetic technology allows clinical geneticists to link an estimated 40% of cases to genetic causes, consensus guidelines in the US and UK are limited to high-resolution chromosome and fragile X testing. A genotype-first model of diagnosis has been proposed, which would routinely assess the genome's copy number variations. As new genetic tests are developed several ethical, legal, and social issues will emerge. Commercial availability of tests may precede adequate understanding of how to use test results, given the complexity of<unk> 's genetics. Metabolic and neuroimaging tests are sometimes helpful, but are not routine. ASD can sometimes be diagnosed by age 14 months, although diagnosis becomes increasingly stable over the first three years of life: for example, a one-year-old who meets diagnostic criteria for ASD is less likely than a three-year-old to continue to do so a few years later. In the UK the National<unk>  Plan for Children recommends at most 30 weeks from first concern to completed diagnosis and assessment, though few cases are handled that quickly in practice. Although the symptoms of<unk>  and ASD begin early in childhood, they are sometimes missed; years later, adults may seek diagnoses to help them or their friends and family understand themselves, to help their employers make adjustments, or in some locations to claim disability living allowances or other benefits. Signs of<unk>  may be more challenging for clinicians to detect in females.<unk> ic females have been shown to engage in masking more frequently than<unk> ic males. Masking may include making oneself perform normative facial expressions and eye contact. A notable percentage of<unk> ic females may be misdiagnosed, diagnosed after a considerable delay, or not diagnosed at all. Conversely, the cost of screening and diagnosis and the challenge of obtaining payment can inhibit or delay diagnosis. It is particularly hard to diagnose<unk>  among the visually impaired, partly because some of its diagnostic criteria depend on vision, and partly because<unk> ic symptoms overlap with those of common blindness syndromes or blindisms. Classification<unk>  is one of the five pervasive developmental disorders (PDD), which are characterized by widespread abnormalities of social interactions and communication, severely restricted interests, and highly repetitive behavior. These symptoms do not imply sickness, fragility, or emotional disturbance. Of the five PDD forms, Asperger syndrome is closest to<unk>  in signs and likely causes; Rett syndrome and childhood disintegrative disorder share several signs with<unk> , but may have unrelated causes; PDD not otherwise specified (PDD-NOS; also called atypical<unk>  is diagnosed when the criteria are not met for a more specific disorder. Unlike with<unk> , people with Asperger syndrome have no substantial delay in language development. The terminology of<unk>  can be bewildering, with<unk> , Asperger syndrome and PDD-NOS often called the<unk>  spectrum disorders (ASD) or sometimes the<unk> ic disorders, whereas<unk>  itself is often called<unk> ic disorder, childhood<unk> , or infantile<unk> . In this article,<unk>  refers to the classic<unk> ic disorder; in clinical practice, though,<unk> , ASD, and PDD are often used interchangeably. ASD, in turn, is a subset of the broader<unk>  phenotype, which describes individuals who may not have ASD but do have<unk> ic-like traits, such as avoiding eye contact. Research into causes has been hampered by the inability to identify biologically meaningful subgroups within the<unk> ic population and by the traditional boundaries between the disciplines of psychiatry, psychology, neurology and pediatrics. Newer technologies such as fMRI and diffusion tensor imaging can help identify biologically relevant phenotypes (observable traits) that can be viewed on brain scans, to help further neurogenetic studies of<unk> ; one example is lowered activity in the fusiform face area of the brain, which is associated with impaired perception of people versus objects. It has been proposed to classify<unk>  using genetics as well as behavior. (For more, see Brett Abrahams, geneticist and neuroscientist) Spectrum<unk>  has long been thought to cover a wide spectrum, ranging from individuals with severe impairments—who may be silent, developmentally disabled, and prone to frequent repetitive behavior such as hand flapping and rocking—to high functioning individuals who may have active but distinctly odd social approaches, narrowly focused interests, and verbose, pedantic communication. Because the behavior spectrum is continuous, boundaries between diagnostic categories are necessarily somewhat arbitrary.
Autism
Schizophrenia
Tourettism
Reactive attachment disorder
Puberphonia
Intellectual disability
Selective mutism
Lesch–Nyhan syndrome