Autism Spectrum Disorder

Clinical picture

• Reduced social reciprocity with limited joint attention, atypical eye contact, and difficulty reading tone, gesture, and facial expression.
• Language ranges from fluent but pedantic and monotone speech to minimal verbal output; echolalia and scripted phrases are common.
• Insistence on sameness produces distress at transitions, rigid routines, and narrow special interests pursued with unusual intensity.
• Stereotyped motor movements such as hand flapping, rocking, spinning, and toe walking often intensify with excitement or stress.
• Sensory hyperreactivity or hyporeactivity to sound, texture, light, and pain drives much observable avoidance and meltdown behavior.
• Camouflaging is common in girls and adults, delaying diagnosis until anxiety, depression, or burnout finally brings them to care.

Criteria snapshot

• Requires all three social communication deficits: social-emotional reciprocity, nonverbal communication, and developing or maintaining relationships.
• Requires at least two of four restricted or repetitive domains: stereotypy, insistence on sameness, fixated interests, and sensory reactivity.
• Symptoms must be present in early development, though impairment may surface only when social demands exceed limited compensatory capacity.
• Severity is rated separately for social communication and for restricted behavior as level 1, 2, or 3 by amount of support required.
• Specifiers cover intellectual impairment, language impairment, associated medical, genetic, or environmental conditions, and catatonia.

Neurobiology

• Heritability estimates of 60-90%; hundreds of risk genes converge on synaptic scaffolding, chromatin remodeling, and transcriptional regulation.
• Syndromic causes include fragile X, tuberous sclerosis, Rett syndrome, and 15q11-13 duplication; chromosomal microarray is first-tier testing.
• Early brain overgrowth across the first 2-3 years is followed by atypical cortical thinning and reduced long-range functional connectivity.
• Excitatory-inhibitory imbalance arising from GABAergic interneuron dysfunction contributes to sensory overload and elevated seizure risk.
• Amygdala and fusiform face area show atypical activation to faces, and superior temporal sulcus underresponds to biological motion.
• Advanced parental age, extreme prematurity, and in utero valproate exposure raise risk; vaccines have been definitively excluded as a cause.

Psychology

• Theory of mind delay impairs inference of others' beliefs and intentions, producing literal, rule-bound interpretation of social situations.
• Weak central coherence biases processing toward detail over gestalt, aiding pattern detection but hindering use of context and meaning.
• Executive dysfunction in set shifting and planning underlies rigidity, transition distress, and difficulty coping with novel demands.
• Predictive coding accounts describe intolerance of prediction error, making unpredictable social and sensory environments intensely aversive.
• Repetitive behavior functions to regulate arousal; suppressing it without offering a replacement raises distress rather than reducing it.

Differential & comorbidity

• Distinguish from social (pragmatic) communication disorder, which lacks restricted repetitive behavior, and from selective mutism and social anxiety.
• Global developmental delay, severe early deprivation, hearing loss, and developmental language disorder can all mimic core social deficits.
• ADHD co-occurs in 30-60%, anxiety disorders in about 40%, intellectual disability in roughly 35%, and epilepsy in 10-30%.
• Gastrointestinal symptoms, sleep-onset insomnia, and avoidant/restrictive food intake are common and often drive the presenting complaint.
• Elopement, self-injurious behavior, and elevated suicide risk in verbally fluent adults require explicit and repeated safety planning.

Pharmacologic treatment

• No medication treats core social communication deficits; agents target irritability, aggression, hyperactivity, and repetitive behavior.
• Risperidone 0.5-3 mg/day and aripiprazole 2-15 mg/day carry FDA approval for irritability associated with autism in ages 5-17.
• Monitor weight, BMI percentile, lipids, glucose, prolactin, and extrapyramidal signs at baseline, at 3 months, then at least annually.
• Methylphenidate helps co-occurring ADHD but with lower response rates and more adverse effects than in ADHD without autism.
• Melatonin 1-6 mg at bedtime improves sleep onset; SSRIs show weak evidence for repetitive behavior and frequently cause activation.

Psychotherapy

• Early intensive behavioral intervention using ABA methods, 20-40 hours weekly for 1-3 years, has the strongest outcome evidence.
• Naturalistic developmental behavioral interventions such as the Early Start Denver Model embed teaching within play and daily routines.
• Speech-language therapy targets pragmatics and, when spoken language is absent, augmentative and alternative communication systems.
• PEERS social skills groups over 14-16 weeks improve peer engagement in adolescents and young adults who have fluent language.
• Adapted CBT using visual supports and concrete language reduces co-occurring anxiety in cognitively able children and adolescents.

Adjunct options

• M-CHAT-R/F screening at 18 and 24 months; ADOS-2 with ADI-R and developmental history anchor diagnostic confirmation.
• Chromosomal microarray and fragile X testing are recommended first-tier genetic workup for every newly diagnosed individual.
• Occupational therapy addresses sensory regulation, self-care, and motor coordination; physical therapy when hypotonia limits mobility.
• Individualized education programs, structured teaching, and visual schedules translate treatment goals into the school day.
• Transition planning from age 14-16 covers vocational training, guardianship or supported decision making, and adult service linkage.

Clinical pearls

• Loss of language or social skills after age 2 warrants neurology referral, not reassurance.
• Ask what function a repetitive behavior serves before trying to extinguish it.
• Fluent speech does not rule out autism; camouflaging delays diagnosis in girls.