ities may hamper learning, especially learning through social interaction or in settings
with peers. In the home, insistence on rout ines and aversion to change, as well as sensory
sensitivities, may interfere with eating and sleeping and make routine care (e.g., haircuts,
dental work) extremely difficult. Adaptive skills are typically below measured IQ. Ex-
treme difficulties in planning, organization , and coping with change negatively impact
academic achievement, even fo r students with above-average intelligence. During adult-
hood, these indivi duals may have difficulties establishing independence because of con-
tinued rigidity and difficulty with novelty.
Many individuals with autism spectrum d isorder, even without intellectual disability,
have poor adult psychosocial functioning as indexed by measures such as independent
living and gainful employment. Functional cons equences in old age are unknown, but so-
cial isolation and communication problems (e .g., reduced help-seeking) are likely to have
consequences for health in older adulthood.
Differential Diagnosis 
Rett syndrome. Disruption of social interaction ma y be observed during the regressive
phase of Rett syndrome (typic ally between 1–4 years of age); thus, a substantial proportion
of affected young girls may ha ve a presentation that meets diagnostic criteria for autism
spectrum disorder. Howe ver, after this period, most individuals with Rett syndrome im-
prove their social communication skills, and auti stic 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 develo pment 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,