Persistent deficits in social communication plus restricted/repetitive behaviors present in early development.
Also known as: autism, ASD, autism spectrum disorder
Overview
A neurodevelopmental disorder characterized by persistent deficits in social communication and social interaction across multiple contexts AND restricted, repetitive patterns of behavior, interests, or activities, with symptoms present in early developmental period and causing clinically significant impairment.
Epidemiology
Prevalence ~1 in 31 US 8-year-olds (CDC ADDM Network, 2022 data published 2025). Male-to-female ratio ~3.4:1, though females may be underdiagnosed. Highly heritable (~80%).
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Question 1PsychiatryMedium
A 3-year-old boy is evaluated for delayed language and atypical social behavior. He makes little eye contact, does not point to share interest, and lines up his toy cars for long periods. He flaps his hands when excited and becomes distressed by changes in routine. He was born at term, and there is no history of neglect. Developmental evaluation confirms autism spectrum disorder. Which of the following best explains this child's disorder?
ALoss of MECP2 function producing regression and hand stereotypies after normal infancy
BAutoimmune destruction of striatal neurons following group A streptococcal infection
CEnvironmental lead neurotoxicity disrupting synaptic pruning in the developing cortex
DDopamine and norepinephrine hypofunction in prefrontal-striatal circuits
EAtypical cortical development and connectivity from polygenic and copy-number variants
Reveal answer & full explanation
Correct answer: E — Atypical cortical development and connectivity from polygenic and copy-number variants
ALoss of MECP2 function producing regression and hand stereotypies after normal infancy
BAutoimmune destruction of striatal neurons following group A streptococcal infection
CEnvironmental lead neurotoxicity disrupting synaptic pruning in the developing cortex
DDopamine and norepinephrine hypofunction in prefrontal-striatal circuits
EAtypical cortical development and connectivity from polygenic and copy-number variants✓
Why Atypical cortical development and connectivity from polygenic and copy-number variants is correct
Autism spectrum disorder is a highly heritable (~80%) neurodevelopmental disorder driven by polygenic inheritance plus copy-number variants and de novo mutations in synaptic and neurodevelopmental gene pathways.
These genetic contributions produce abnormal cortical development and atypical neural connectivity, particularly in regions subserving social cognition and language, explaining the social-communication deficits and restricted, repetitive behaviors present from the early developmental period.
Why the others are wrong
Loss of MECP2 function producing regression and hand stereotypies after normal infancy — this is Rett syndrome, which occurs almost exclusively in girls and requires loss of previously acquired language and purposeful hand use after a period of normal early development; this boy is male and has had persistent deficits without regression.
Autoimmune destruction of striatal neurons following group A streptococcal infection describes the PANDAS/Sydenham chorea mechanism (post-streptococcal basal ganglia autoimmunity producing abrupt-onset tics or OCD), not the early developmental, polygenic process of ASD.
Environmental lead neurotoxicity disrupting synaptic pruning in the developing cortex — lead exposure produces nonspecific cognitive, attentional, and behavioral impairment rather than the specific social-communication deficits and restricted, repetitive behaviors that define ASD, and no exposure is described.
Dopamine and norepinephrine hypofunction in prefrontal-striatal circuits — this is the catecholamine model of ADHD, which often co-occurs with ASD and is treated with stimulants, but inattention and hyperactivity do not explain his core deficits in joint attention and eye contact or his restricted, repetitive behaviors such as lining up toys, hand flapping, and distress at changes in routine.
Question 2PsychiatryMedium
A 2-year-old boy is brought in by his parents for delayed speech and limited social engagement. He uses no meaningful words, rarely makes eye contact, and does not point to show interest. He lines up his toy cars repeatedly and becomes very distressed when his routine changes, and he flaps his hands when excited. A failed M-CHAT-R/F prompted referral, and developmental evaluation confirms autism spectrum disorder. Audiology and lead screening are normal. He has no aggression, self-injury, or sleep disturbance. Which of the following is the most appropriate initial management?
ARefer for early intensive behavioral therapy
BDefer intervention and reassess in six months
CPrescribe sertraline for repetitive behaviors
DObtain brain MRI and EEG before referral
EPrescribe risperidone for distress with change
Reveal answer & full explanation
Correct answer: A — Refer for early intensive behavioral therapy
ARefer for early intensive behavioral therapy✓
BDefer intervention and reassess in six months
CPrescribe sertraline for repetitive behaviors
DObtain brain MRI and EEG before referral
EPrescribe risperidone for distress with change
Why Refer for early intensive behavioral therapy is correct
Early intensive behavioral intervention (ABA, naturalistic developmental behavioral interventions such as the Early Start Denver Model) plus speech-language and occupational therapy is the guideline-defined first-line management for a young child newly diagnosed with ASD.
Per AAP, intervention should begin as soon as ASD is suspected, and services should not be delayed pending formal diagnosis, because intervention before age 3 produces the largest developmental gains.
This child has core social-communication deficits and restricted/repetitive behaviors without irritability, anxiety, or sleep problems, so behavioral and developmental therapy is the appropriate initial step.
Why the others are wrong
Defer intervention and reassess in six months — the diagnosis is already established, and AAP guidance is to start services as soon as ASD is suspected; waiting six months at age 2 forfeits the developmental window in which intervention produces the largest gains.
Obtain brain MRI and EEG before referral — neuroimaging and EEG are not part of the routine ASD evaluation and are reserved for focal neurologic deficits, dysmorphic features, or suspected seizures, none of which are present here, so ordering them would only postpone therapy.
Prescribe sertraline for repetitive behaviors is incorrect because SSRIs are reserved for comorbid anxiety or OCD; evidence does not support them for core repetitive behaviors, and this child has no anxiety disorder.
Prescribe risperidone for distress with change — risperidone and aripiprazole are the only FDA-approved medications in ASD, which makes them tempting, but the approval is for irritability (aggression, self-injury, severe tantrums) in older children, not core symptoms or distress with routine change in a 2-year-old; antipsychotics carry weight-gain and metabolic risk and never replace early behavioral intervention.
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Genetic syndromes: fragile X, tuberous sclerosis, Rett (girls), 22q11.2 deletion
Valproate exposure in utero
Pathophysiology
Polygenic and copy-number variant contributions; abnormal cortical development and connectivity, particularly in regions subserving social cognition and language. Synaptic and neurodevelopmental gene pathways implicated.
Clinical presentation
Symptoms
Social communication: reduced social-emotional reciprocity, atypical nonverbal communication, difficulty developing and maintaining relationships appropriate to developmental level
Restricted/repetitive: stereotyped/repetitive motor movements or speech, insistence on sameness/routines, highly restricted fixated interests, hyper- or hyporeactivity to sensory input
Variable language ability — from non-speaking to fluent; pragmatic deficits common even in fluent speakers
Common co-occurrences: ID, ADHD, anxiety, epilepsy, GI symptoms, sleep disorders
Signs / physical exam
Reduced eye contact, limited joint attention, atypical play (lining up toys, lack of pretend play)
Echolalia, scripted speech
Hand-flapping, rocking, toe-walking
Sensory sensitivities (sound, texture, light)
Differential diagnosis
Intellectual disability without ASD — Cognitive impairment without disproportionate social communication deficits
Language disorder / social communication disorder — Language or pragmatic deficits without restricted/repetitive behaviors
ADHD — Inattention and impulsivity without core social-communication impairment; commonly co-occurs
Reactive attachment disorder — History of severe neglect; social withdrawal improves with stable caregiving
Selective mutism — Speaks at home but not in select settings; otherwise typical social development
Hearing impairment — Screen audiology in any child with language delay
Anxiety / OCD — Distinguish ego-dystonic compulsions from autistic restricted interests, which are typically ego-syntonic
Diagnostic workup
Diagnostic criteria
DSM-5-TR: (A) Persistent deficits in social communication and interaction across contexts — all three subcriteria (reciprocity, nonverbal communication, relationships); (B) Restricted/repetitive patterns — >=2 of four (stereotypies, insistence on sameness, restricted interests, sensory differences); (C) Symptoms in early developmental period; (D) Clinically significant impairment; (E) Not better explained by ID alone. Specify severity (levels 1-3 by support needs), with/without ID, language impairment, medical/genetic conditions, or catatonia. Screening: M-CHAT-R/F at 18 and 24 months.
Labs
Screen lead level, audiology evaluation
Genetic evaluation: chromosomal microarray and fragile X testing recommended for all; consider whole exome based on dysmorphology
Metabolic workup if atypical or multiple regressions, motor regression, significant hypotonia, or dysmorphic features
EEG if seizures suspected
Imaging
MRI not routine; obtain if focal findings, atypical regression (after age 2-3, motor regression, or multiple regressions), seizures, microcephaly, or macrocephaly with neurologic signs; the typical language/social regression at 18-24 months seen in about a quarter of children with ASD does not by itself require MRI or EEG
Higher rates of suicidality, especially in adults with ASD without ID
Caregiver burden
PANCE pearls
All children should be screened for ASD at 18 and 24 months using M-CHAT-R/F per AAP; refer for diagnostic evaluation if positive — do not wait.
Early intervention before age 3 produces the largest gains; do not delay services for formal diagnosis.
Catatonia is increasingly recognized in adolescents/adults with ASD — consider in regression with mutism, posturing.
Adults with ASD often present first with anxiety or depression; ask about lifelong social communication patterns.
Absent joint attention by 12-18 months (no pointing to show interest, no following of gaze) is one of the earliest and most specific red flags, along with poor response to name; other red flags are no babbling or gestures by 12 months, no single words by 16 months, no spontaneous 2-word phrases by 24 months, and any loss of language or social skills at any age, which warrants immediate evaluation.
References
AAP 2020 — Hyman SL et al. Identification, Evaluation, and Management of Children With Autism Spectrum Disorder. Pediatrics 2020
AACAP 2014 — Volkmar F, Siegel M, Woodbury-Smith M, et al; AACAP Committee on Quality Issues. Practice Parameter for the Assessment and Treatment of Children and Adolescents With Autism Spectrum Disorder. J Am Acad Child Adolesc Psychiatry. 2014;53(2):237-257
DSM-5-TR — American Psychiatric Association. DSM-5-TR (2022)
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