Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder defined by persistent deficits in social communication and social interaction plus restricted, repetitive patterns of behaviour, interests or activities (RRBs), with onset in the early developmental period. For NEET PG it is a reliable source of questions on DSM-5 criteria, early red flags, screening tools (M-CHAT, ISAA), comorbidities (intellectual disability, epilepsy) and the deliberate collapse of older subtypes (Asperger's, PDD-NOS) into a single spectrum.

Definition and the shift to a "spectrum"

ASD is a clinical, behaviourally-defined diagnosis — there is no confirmatory biological test. The word "spectrum" reflects the wide variation in severity, language ability and intellectual function. The landmark change tested in exams is that DSM-5 (2013) abolished the older subtypes that existed in DSM-IV — Autistic disorder, Asperger's syndrome, Childhood disintegrative disorder (Heller syndrome) and PDD-NOS — folding them all into a single diagnosis: Autism Spectrum Disorder. ICD-11 mirrors this with "Autism spectrum disorder" as a unitary category.

High-yield: In DSM-5, the previous three domains became two — the old "social" and "communication" domains were merged into a single social-communication domain, and RRBs form the second. So ASD = 2 core domains (social-communication deficits + repetitive/restricted behaviours).

Key epidemiological facts: prevalence is rising (now ~1 in 36–44 children in Western data, lower reported figures in India owing to under-recognition). Male:female ratio ≈ 4:1. It is the most heritable of the major psychiatric/neurodevelopmental disorders (twin concordance very high; sibling recurrence risk ~10–20%).

Etiology and pathophysiology

ASD is strongly genetic and multifactorial; there is no single cause.

Category	Examples / associations
Genetic syndromes (~10–20%)	Fragile X (commonest single-gene cause), Tuberous sclerosis, Rett syndrome (MECP2), Down syndrome, Angelman, Phenylketonuria (untreated)
Copy-number variants	15q11-13 duplication, 16p11.2 deletion/duplication, 22q13 (SHANK3)
Prenatal exposures	Sodium valproate in pregnancy, thalidomide, congenital rubella, congenital CMV
Perinatal	Extreme prematurity, very low birth weight, perinatal hypoxia
Parental	Advanced paternal (and maternal) age

High-yield: MMR vaccine does NOT cause autism. The 1998 Wakefield paper was fraudulent and retracted; multiple large studies show no link. This is a favourite single-best-answer "myth-buster."

Neurobiology (conceptual, occasionally asked): early brain overgrowth in the first 2–3 years (increased head circumference/brain volume), abnormal synaptic pruning, and altered connectivity (local over-connectivity, long-range under-connectivity). Implicated systems include glutamatergic/GABAergic imbalance and the mirror-neuron/social-brain network. EEG abnormalities and epilepsy are common, reflecting cortical excitability.

Clinical features

Manifestations cluster into the two DSM-5 domains.

A. Social-communication deficits (all three required)

1. Deficits in social-emotional reciprocity — poor back-and-forth conversation, reduced sharing of interests/emotions.
2. Deficits in nonverbal communicative behaviours — abnormal eye contact, reduced gestures, poor integration of facial expression and body language.
3. Deficits in developing, maintaining and understanding relationships — difficulty with imaginative play, absent interest in peers.

B. Restricted, repetitive behaviours (≥ 2 of 4 required)

1. Stereotyped/repetitive motor movements, speech or object use — hand-flapping, lining up toys, echolalia.
2. Insistence on sameness, inflexible routines, ritualised behaviour (distress at small changes).
3. Highly restricted, fixated interests abnormal in intensity/focus.
4. Hyper- or hypo-reactivity to sensory input — indifference to pain/temperature, adverse response to specific sounds/textures (a feature newly added in DSM-5).

Other common clinical clues: lack of joint attention (not pointing to show interest, not following a point), failure to respond to name, absent pretend/symbolic play, loss of previously acquired language (regressive presentation in ~25%), preference for solitary play.

Early red flags (developmental surveillance)

These age-anchored milestones are extremely high-yield and frequently asked verbatim. Any one of them warrants evaluation:

Age	Red flag (an indication for evaluation)
6 months	No big smiles or warm, joyful expressions
9 months	No back-and-forth sharing of sounds, smiles, facial expressions
12 months	No babbling; no gestures (pointing, waving, reaching)
16 months	No single words
24 months	No meaningful (non-echolalic) two-word phrases
Any age	Loss/regression of speech, babbling or social skills

High-yield: Memorise the trio — no babbling by 12 months, no single words by 16 months, no 2-word phrases by 24 months, OR any loss of skills at any age = red flags mandating referral. The regression clue ("a child who spoke a few words at 14 months and then stopped") is a classic stem.

Screening and diagnosis

ASD diagnosis is clinical, based on history, developmental assessment and direct observation against DSM-5 criteria. Investigations are done to find an underlying cause or comorbidity, not to diagnose ASD itself.

Stepwise diagnostic approach: Developmental surveillance at every visit → routine M-CHAT-R/F screening at 18 and 24 months → positive screen or red flags → comprehensive multidisciplinary evaluation (paediatrician/developmental specialist + audiology + psychology) → apply DSM-5 criteria + standardised tools (ADOS, ADI-R) → assign severity level (1–3) and specifiers → targeted aetiological workup.

Screening / assessment tools to know:

Tool	Purpose / note
M-CHAT-R/F	Modified Checklist for Autism in Toddlers — parent-report screening at 16–30 months (best at 18 & 24 mo)
CHAT	Original Checklist for Autism in Toddlers (18 mo)
ISAA	Indian Scale for Assessment of Autism — Indian Govt-validated tool used for diagnosis grading and disability certification (≥40% = disability benefit) in children 3–22 years
INCLEN / INDT-ASD	Indian diagnostic tool developed for the Indian setting
ADOS	Autism Diagnostic Observation Schedule — gold-standard observational assessment
ADI-R	Autism Diagnostic Interview-Revised — structured parental interview
CARS	Childhood Autism Rating Scale — severity rating

High-yield (India-specific): ISAA = Indian Scale for Assessment of Autism, the officially adopted tool for certifying autism-related disability in India (used 3–22 yrs). M-CHAT is the screening instrument; ADOS is the diagnostic gold standard.

Investigations to look for cause/comorbidity (not to "rule in" ASD):

• Hearing assessment (audiometry/BERA) — mandatory in any child with language delay, to exclude deafness.
• Vision evaluation.
• Genetic testing — chromosomal microarray (first-line), Fragile X (FMR1) testing, ± whole-exome sequencing.
• Metabolic / Wood's lamp / neuroimaging / EEG — only if features suggest (regression, seizures, dysmorphism, neurocutaneous stigmata).
• Lead level if pica.

DSM-5 severity levels

Severity is rated separately for each of the two domains:

Level	Label	Support needed
Level 1	"Requiring support"	Noticeable difficulty initiating social interaction; inflexibility causes interference (≈ old Asperger's/high-functioning)
Level 2	"Requiring substantial support"	Marked deficits even with support; frequent RRBs
Level 3	"Requiring very substantial support"	Severe deficits; very limited initiation; extreme difficulty coping with change

Specifiers to record: with/without intellectual impairment, with/without language impairment, associated medical/genetic condition, and catatonia.

Management

There is no curative drug. Management is early, intensive, behavioural and multidisciplinary — earlier intervention gives better outcomes (driving the push for screening at 18–24 months).

Pillars of management:

1. Behavioural / educational (cornerstone): Applied Behaviour Analysis (ABA), Early Start Denver Model, TEACCH, structured special education with an individualised plan.
2. Speech-language therapy and occupational therapy (sensory integration).
3. Social skills training; parent training and support.
4. Pharmacotherapy — only for associated/troublesome symptoms, not core deficits.

High-yield: The only two drugs FDA-approved for irritability/aggression/self-injury in autism are the atypical antipsychotics Risperidone and Aripiprazole. They treat associated symptoms, not the core disorder.

Other symptom-targeted agents: methylphenidate/atomoxetine for comorbid ADHD; SSRIs for anxiety/repetitive behaviours (modest evidence); melatonin for sleep disturbance.

Comorbidities and complications

ASD rarely travels alone — comorbidity is the rule and a rich source of questions.

• Intellectual disability — in roughly 30–50% of cases (DSM-5 records this as a specifier).
• Epilepsy / seizures — markedly increased; bimodal peaks in early childhood and adolescence; up to a quarter, higher with intellectual disability.
• ADHD — very common; DSM-5 now permits the dual diagnosis (DSM-IV forbade it).
• Anxiety disorders, OCD, depression (especially in higher-functioning adolescents).
• Sleep disorders, GI problems (constipation, feeding selectivity), pica.
• Macrocephaly; motor incoordination; catatonia in adolescence.

High-yield: The two most-tested medical comorbidities are intellectual disability and epilepsy. A child with ASD plus seizures plus hypopigmented (ash-leaf) macules → think tuberous sclerosis.

Key differentials

Condition	Distinguishing feature
Intellectual disability (alone)	Global delay but social relatedness preserved and proportionate to mental age; no qualitative social-communication deficit
Specific language / expressive disorder	Language delayed but social reciprocity, gestures and pretend play intact
Hearing impairment / deafness	Responds to visual cues, normal social engagement once communication enabled — always test hearing first
Rett syndrome	Girls; normal then regression, loss of purposeful hand use + stereotypic hand-wringing, deceleration of head growth; MECP2 mutation
Childhood disintegrative disorder (Heller)	Normal development to ≥2 yrs then dramatic regression across multiple domains (now within ASD/separate in ICD)
Reactive attachment disorder	History of severe neglect; improves with a nurturing environment
Selective mutism / social anxiety	Normal communication in comfortable settings
Stereotypic movement disorder	Repetitive movements without the social-communication deficits
Schizophrenia (childhood)	Hallucinations/delusions; later onset; after a period of normal development

Asperger's syndrome (a frequent distractor): historically described autistic social impairment + RRBs but with NO clinically significant language or cognitive delay (normal/high IQ). In DSM-5 it is no longer a separate diagnosis — such children are now diagnosed as ASD, often Level 1 (without language/intellectual impairment).

High-yield: Classic exam contrast — Autism vs Asperger's: language delay and cognitive impairment are present in classic autism and absent in Asperger's; both are now subsumed under ASD in DSM-5/ICD-11.

Mnemonic

For DSM-5 core features, use "SOCIAL + 3 R's":

• Social-emotional reciprocity deficit
• Observable nonverbal communication deficit (eye contact, gestures)
• Connecting/relationship deficits
• plus the RRBs: Repetitive movements/speech, Rigidity (sameness/routines) & restricted interests, Reactivity to sensory input.

A handy red-flag aid: "12-16-24" → no babbling by 12, no words by 16, no phrases by 24 (or any regression).

Recently asked / exam angle

• Single best DSM-5 fact: ASD has two symptom domains (social-communication + RRBs), and subtypes like Asperger's/PDD-NOS were eliminated.
• Earliest reliable red flag commonly tested: lack of joint attention / not pointing & no babbling by 12 months, and no single words by 16 months.
• Screening tool at 18–24 months = M-CHAT-R/F; Indian diagnostic/disability tool = ISAA.
• Drugs FDA-approved for irritability in ASD = Risperidone and Aripiprazole (core symptoms have no drug).
• MMR vaccine–autism link is disproven (Wakefield, retracted) — recurring myth-buster MCQ.
• Commonest single-gene cause = Fragile X; valproate in pregnancy is a recognised teratogenic cause.
• Most important first investigation in a child with language delay = hearing test (BERA).
• Comorbidity questions: ASD + seizures + ash-leaf macules → tuberous sclerosis; ASD + girl + hand-wringing + head-growth deceleration → Rett.

Rapid revision

1. ASD = persistent social-communication deficits + restricted/repetitive behaviours; clinical diagnosis, no lab test.
2. DSM-5: two domains; Asperger's, PDD-NOS, CDD abolished → single spectrum; severity Levels 1–3.
3. M:F ≈ 4:1; highly heritable; MMR does not cause autism.
4. Red flags: no babbling/gestures by 12 mo, no single words by 16 mo, no 2-word phrases by 24 mo, any loss of skills.
5. Joint attention deficit (no pointing/showing) is an early, sensitive sign.
6. M-CHAT-R/F = screening at 16–30 months (esp. 18 & 24).
7. ISAA = Indian Scale for Assessment of Autism → diagnosis grading + disability certification (3–22 yrs); ADOS = observational gold standard, ADI-R = parent interview.
8. Always test hearing in a child with language delay; do chromosomal microarray + Fragile X for aetiology.
9. Management = early, intensive behavioural therapy (ABA), speech/OT, special education; no curative drug.
10. Risperidone & Aripiprazole — only FDA-approved drugs, for irritability/aggression, not core deficits.
11. Comorbidities: intellectual disability (~30–50%) and epilepsy are the big two; ADHD now co-diagnosable.
12. Commonest single-gene cause Fragile X; prenatal valproate a recognised risk; differentiate from Rett (MECP2, hand-wringing, girls) and isolated language/hearing disorders.