Autism spectrum disorder (ASD)

Autism spectrum disorder is diagnosed on two core domains. The first is persistent difficulty with social communication and social interaction across contexts — reduced social-emotional reciprocity, differences in nonverbal communication such as eye contact and gesture, and difficulty developing and maintaining relationships. The second is restricted, repetitive patterns of behavior, interests, or activities, which may include stereotyped movements or speech, insistence on sameness and routines, highly focused interests, and unusual responses to sensory input.

The word spectrum reflects how much presentation varies. Some individuals have significant intellectual disability and little spoken language; others have average or above-average intelligence and fluent speech alongside marked social and sensory differences. DSM-5 consolidated several earlier diagnoses, including autistic disorder and Asperger's disorder, into the single ASD category and added severity levels based on how much support a person requires in each domain.

Symptoms must be present in the early developmental period, though they may not become fully apparent until social demands exceed a child's capacities. Diagnosis is behavioral, based on developmental history and structured observation rather than a laboratory test, and screening in primary care is recommended in the toddler years. Twin and family studies indicate strong heritability, with many genes of small effect plus some single-gene and chromosomal conditions such as fragile X syndrome. Extensive research has found no link between vaccines and autism. Intervention centers on behavioral, developmental, educational, speech, and occupational therapy, with earlier support associated with better functional outcomes.

ASD appears on several exams. AP Psychology covers it among neurodevelopmental disorders and asks about diagnostic criteria and treatment approaches. USMLE Step 1 behavioral science tests onset, core features, and associated genetic conditions. NPTE-PTA candidates encounter it in pediatrics, where motor coordination, sensory processing, and communication considerations shape how therapy is delivered.