Rett syndrome. Disruption of social interaction may be observed during the regressive phase of Rett syndrome (typically between 1—4 years of age); thus, a substantial proportion spectrum disorder. However, after this period, most individuals with Rett syndrome im— prove their social communication skills, and autistic features are no longer a major area of concern. Consequently, autism spectrum disorder should be considered only when all di- agnostic criteria are met.
Selective mutism. In selective mutism, early development is not typically disturbed.
The affected child usually exhibits appropriate communication skills in certain contexts and settings. Even in settings where the child is mute, social reciprocity is not impaired, nor are restricted or repetitive patterns of behavior present.
Language disorders and social (pragmatic) communication disorder. In some forms of language disorder, there may be problems of communication and some secondary so- cial difficulties. However, specific language disorder is not usually associated with abnor— mal nonverbal communication, nor with the presence of restricted, repetitive patterns of behavior, interests, or activities.
but does not show restricted and repetitive behavior or interests, criteria for social (prag- matic) communication disorder, instead of autism spectrum disorder, may be met. The di- agnosis of autism spectrum disorder supersedes that of social (pragmatic) communication disorder whenever the criteria for autism spectrum disorder are met, and care should be taken to enquire carefully regarding past or current restricted/ repetitive behavior.
disorder. Intellectual disability without autism spectrum disorder may be difficult to differentiate from autism spectrum disorder in very young children. Individuals with in- challenge for differential diagnosis, since repetitive behavior often occurs in such individ- uals as well. A diagnosis of autism spectrum disorder in an individual with intellectual disability is appropriate when social communication and interaction are significantly im- paired relative to the developmental level of the individual’s nonverbal skills (e.g., fine motor skills, nonverbal problem solving). In contrast, intellectual disability is the appropri- ate diagnosis when there is no apparent discrepancy between the level of social-commu- nicative skills and other intellectual skills.
Stereotypic movement disorder. Motor stereotypies are among the diagnostic charac- teristics of autism spectrum disorder, so an additional diagnosis of stereotypic movement disorder is not given when such repetitive behaviors are better explained by the presence of autism spectrum disorder. However, when stereotypies cause self—injury and become a focus of treatment, both diagnoses may be appropriate.
Attention-deficit/hyperactivity disorder. Abnormalities of attention (overly focused or easily distracted) are common in individuals with autism spectrum disorder, as is hy- peractivity. A diagnosis of attention-deficit/hyperactivity disorder (ADHD) should be dividuals of comparable mental age.
Schizophrenia. Schizophrenia with childhood onset usually develops after a period of normal, or near normal, development. A prodromal state has been described in which so- cial impairment and atypical interests and beliefs occur, which could be confused with the social deficits seen in autism spectrum disorder. Hallucinations and delusions, which are defining features of schizophrenia, are not features of autism spectrum disorder. How- ever, clinicians must take into account the potential for individuals with autism spectrum disorder to be concrete in their interpretation of questions regarding the key features of schizophrenia (e.g., ”Do you hear voices when no one is there?” ”Yes [on the radio]”).