Autism Spectrum Disorder (ASD)

1. Clinical Overview

Summary

Autism Spectrum Disorder (ASD) is a lifelong neurodevelopmental condition characterised by persistent deficits in social communication and social interaction across multiple contexts, together with restricted, repetitive patterns of behaviour, interests, or activities. [1,2] The term "spectrum" reflects the wide heterogeneity in presentation, ranging from individuals requiring very substantial support to those with minimal support needs who may live independently. ASD typically manifests in early childhood (before age 3 years), though diagnosis may be delayed until school age or adulthood, particularly in females and those without intellectual disability. [3]

The global prevalence has increased substantially over recent decades to approximately 1 in 36 to 1 in 100 children, likely reflecting improved awareness, broadened diagnostic criteria (DSM-5), and enhanced recognition of subtler presentations. [4,5] The male-to-female ratio is approximately 4:1, though emerging evidence suggests females may be systematically underdiagnosed due to differing phenotypic presentation and social camouflaging. [6]

ASD has a strong genetic basis (heritability 80-90%) but is highly polygenic, with contributions from hundreds of common and rare genetic variants, de novo mutations, and copy number variants. [7] Environmental risk factors include advanced parental age, prematurity, prenatal valproate exposure, and maternal infection during pregnancy, though the MMR vaccine has been definitively exonerated following the retraction of Wakefield's fraudulent study. [8]

Early intervention is the cornerstone of management, with strong evidence supporting structured developmental and behavioural interventions such as the Early Start Denver Model (ESDM) and naturalistic developmental behavioural interventions (NDBIs). [9] There is no pharmacological treatment for core ASD symptoms, but medications may be used judiciously for comorbidities such as ADHD, anxiety, or severe aggression. [10] Outcomes are highly variable, with intellectual ability and language development being the strongest predictors of long-term independence.

Key Facts

Clinical Pearls

"Triad to Dyad Transition": DSM-5 (2013) moved from the Wing's Triad (social interaction, communication, imagination) to a two-domain model: (1) Social communication and social interaction, and (2) Restricted, repetitive behaviours. This reflects research showing difficulties in social communication and interaction are inseparable. [1]

"Think ASD in Girls with Anxiety": Females with ASD are more likely to exhibit internalising symptoms (anxiety, depression) and camouflaging (conscious or unconscious masking of autistic traits), leading to delayed or missed diagnoses. Consider ASD in girls with social anxiety, eating disorders, or peer relationship difficulties. [6]

"Regression Is a Red Flag": Loss of previously acquired language or social skills (occurring in ~30% of ASD cases between 15-24 months) warrants investigation for Rett syndrome, Landau-Kleffner syndrome, or neurometabolic disorders. Always obtain chromosomal microarray and consider EEG. [12]

"No MMR Link — Wakefield Fraud": The MMR vaccine does NOT cause autism. Wakefield's 1998 Lancet study was fraudulent, retracted, and numerous large epidemiological studies have found no association. This must be communicated clearly to families. [8]

"Sensory Issues Are Core, Not Secondary": DSM-5 recognises hyper- or hypo-reactivity to sensory input (or unusual interest in sensory aspects of environment) as part of core diagnostic criteria (Domain B), not just associated features. [1]

"Early Intervention Matters": Initiation of intensive behavioural intervention before age 3 years is associated with significantly better cognitive, language, and adaptive outcomes. The "critical window" is real. [9]

"ADOS-2 Is Gold Standard": The Autism Diagnostic Observation Schedule, 2nd edition (ADOS-2) is the most widely used standardised observational assessment. However, diagnosis is clinical and multidisciplinary, not reliant on any single test. [13]

"Avoid Antipsychotics Unless Severe": Risperidone and aripiprazole have FDA approval for irritability/aggression in ASD, but carry significant metabolic and neurological side effects. Reserve for severe aggression or self-injury unresponsive to behavioural interventions. [10]

---

2. Epidemiology

Prevalence

Trend Over Time: Prevalence estimates have increased dramatically since the 1990s. This is NOT due to a true increase in incidence, but rather:

• Broadened diagnostic criteria (DSM-5 inclusion of Asperger's/PDD-NOS)
• Improved awareness among professionals and public
• Better recognition of subtler presentations
• Increased availability of diagnostic services
• Diagnostic substitution (reclassification from intellectual disability) [5]

Demographics

Risk Factors

Exam Detail: #### Genetic Risk Factors

Heritability: Twin and family studies estimate heritability at 80-90%, among the highest of psychiatric conditions. [7] However, ASD is highly polygenic:

• 100 genes implicated (e.g., CHD8, SCN2A, SHANK3, NRXN1)
• Hundreds of common variants each contributing small effect sizes
• Rare de novo mutations (10-20% of cases)
• Copy number variants (CNVs): deletions/duplications at 15q11-13, 16p11.2, 22q11.2

Environmental Risk Factors

Definitively Refuted:

• MMR vaccine: No association in multiple large studies (total n 1 million) [8]
• Thimerosal (mercury preservative): Removed from vaccines since 2001; no decrease in ASD prevalence

Comorbidities

---

3. Aetiology and Pathophysiology

Genetic Architecture

Exam Detail: ASD is one of the most heritable neurodevelopmental disorders (h² = 80-90%), but its genetic architecture is highly complex and heterogeneous. [7]

Classes of Genetic Variation

Key Genes and Pathways:

• Chromatin remodelling: CHD8, ADNP, ARID1B (transcriptional regulation)
• Synaptic function: SHANK2, SHANK3, NLGN3, NLGN4, NRXN1 (synaptic scaffolding, cell adhesion)
• Ion channels: SCN2A, CACNA1C, KCNQ2 (neuronal excitability)
• Protein synthesis: FMR1 (fragile X mental retardation protein; RNA-binding)
• mTOR pathway: TSC1, TSC2, PTEN (tuberous sclerosis, macrocephaly-ASD)

Parental Age Effect: Advanced paternal age is associated with increased risk, likely due to accumulation of de novo mutations in spermatogonia over time. [7]

Neurobiology

Exam Detail: #### Brain Development and Connectivity

Structural Findings:

• Macrocephaly: ~20% of children with ASD have head circumference 97th percentile [17]
• Accelerated early brain growth: Overgrowth in first 2 years, followed by plateau
• Increased brain volume: Particularly frontal and temporal lobes
• Altered cortical thickness: Regional variations; some areas thickened, others thinned

Connectivity Abnormalities (most consistent finding):

• Reduced long-range connectivity: Impaired communication between distant brain regions (frontal-posterior underconnectivity)
• Increased local connectivity: Enhanced short-range connections within specific regions
• White matter microstructure: Altered fractional anisotropy on diffusion tensor imaging (DTI)

Functional Imaging (fMRI):

• Reduced social brain network activation: Fusiform face area, superior temporal sulcus, amygdala during social tasks
• Atypical reward processing: Reduced ventral striatum activation to social rewards (faces) but intact or enhanced activation to non-social rewards
• Default mode network (DMN): Altered connectivity and maturation of DMN (self-referential processing network)

Synaptic and Circuit-Level Mechanisms

Excitation-Inhibition (E-I) Imbalance Hypothesis: [18]

• Altered ratio of excitatory (glutamatergic) to inhibitory (GABAergic) neurotransmission
• Supported by findings in animal models (e.g., Cntnap2, Shank3 knockout mice)
• May underlie sensory hypersensitivity, seizures, and cognitive rigidity

Synaptic Dysfunction:

• Mutations in synaptic genes (SHANK3, NLGN, NRXN) disrupt synaptic formation, maintenance, and plasticity
• Altered dendritic spine density and morphology in post-mortem studies

Critical Period Dysregulation:

• Evidence from animal models that early developmental windows (critical periods) for sensory and social learning may be disrupted or shifted in ASD

Neuroinflammation and Immune Dysregulation

Maternal Immune Activation (MIA):

• Prenatal infection or inflammation may activate maternal immune response, altering fetal brain development
• Cytokines (IL-6, IL-17) implicated in animal models
• Epidemiological support: maternal infection during pregnancy weakly associated with ASD risk

Microglial Activation:

• Post-mortem studies show activated microglia (brain immune cells) in some individuals with ASD
• Unclear if primary or secondary phenomenon

Environmental Factors and Gene-Environment Interaction

Prenatal Valproate Exposure: [16]

• Most robust environmental risk factor (OR 3-5)
• Dose-dependent effect; 10% of exposed children develop ASD
• Mechanism: histone deacetylase (HDAC) inhibition, altered gene expression during neurodevelopment

Prematurity and Perinatal Complications:

• Likely mediated through disrupted brain maturation, hypoxia-ischemia, inflammation
• May interact with genetic susceptibility

Gut Microbiome:

• Emerging hypothesis: altered gut microbiota composition in ASD
• "Gut-brain axis" may influence behaviour via immune modulation, metabolite production
• Evidence remains preliminary; causality unclear

---

4. Clinical Presentation

DSM-5 Diagnostic Criteria (2013)

ASD requires both criterion A and criterion B, plus criteria C, D, and E. [1]

Criterion A: Persistent deficits in social communication and social interaction across multiple contexts

A1. Deficits in social-emotional reciprocity:

• Abnormal social approach and failure of normal back-and-forth conversation
• Reduced sharing of interests, emotions, or affect
• Failure to initiate or respond to social interactions

A2. Deficits in nonverbal communicative behaviours:

• Poorly integrated verbal and nonverbal communication
• Abnormalities in eye contact and body language
• Deficits in understanding and use of gestures
• Total lack of facial expressions and nonverbal communication

A3. Deficits in developing, maintaining, and understanding relationships:

• Difficulties adjusting behaviour to suit various social contexts
• Difficulties in sharing imaginative play or making friends
• Absence of interest in peers

Criterion B: Restricted, repetitive patterns of behaviour, interests, or activities

Must have ≥2 of the following:

B1. Stereotyped or repetitive motor movements, use of objects, or speech:

• Simple motor stereotypies (hand flapping, finger flicking, body rocking)
• Lining up toys or flipping objects
• Echolalia (immediate or delayed repetition of words or phrases)
• Idiosyncratic phrases

B2. Insistence on sameness, inflexible adherence to routines, or ritualised patterns of behaviour:

• Extreme distress at small changes
• Difficulties with transitions
• Rigid thinking patterns
• Greeting rituals
• Need to take same route or eat same food every day

B3. Highly restricted, fixated interests that are abnormal in intensity or focus:

• Strong attachment to or preoccupation with unusual objects
• Excessively circumscribed or perseverative interests (e.g., memorising train timetables, dinosaur facts)

B4. Hyper- or hypo-reactivity to sensory input OR unusual interest in sensory aspects of environment:

• Apparent indifference to pain or temperature
• Adverse response to specific sounds or textures
• Excessive smelling or touching of objects
• Visual fascination with lights or movement

Criterion C: Symptoms present in early developmental period

• Typically recognised in second year of life
• May not become fully manifest until social demands exceed capacities
• May be masked by learned strategies in later life

Criterion D: Symptoms cause clinically significant impairment

• In social, occupational, or other important areas of current functioning

Criterion E: Not better explained by intellectual disability or global developmental delay

• Social communication should be below expected level for general developmental level

DSM-5 Severity Levels

Clinical Phenotypes and Presentation by Age

Exam Detail: #### Infancy (0-12 months)

Retrospective parental report and video analysis studies suggest early red flags:

• Reduced eye contact and visual tracking of faces
• Reduced responsiveness to name
• Reduced social smiling (may be present but less frequent/spontaneous)
• Reduced babbling (especially consonant babbling and vocalisations directed at caregiver)
• Unusual sensory behaviours (e.g., lack of startle to loud noises, or extreme distress)

Clinical Pearl: Diagnosis in the first year is challenging and often unreliable. Most children are identified in the second year.

Toddlerhood (12-36 months)

Most common age for parental concern and presentation:

Social Communication Red Flags:

• Reduced pointing (especially protodeclarative pointing to share interest, rather than protoimperative pointing to request)
• Failure to respond to name (by 12 months, most typically developing children turn when name is called)
• Lack of joint attention (sharing attention to an object/event with another person via eye gaze, pointing, showing)
• Absent or delayed language (no babbling by 12 months, no words by 16 months, no two-word phrases by 24 months)
• Reduced or absent symbolic play (pretend play, e.g., feeding a doll, using a block as a car)
• Lack of imitation (motor imitation of actions, facial expressions)

Restricted/Repetitive Behaviours:

• Hand flapping, body rocking, spinning
• Lining up toys obsessively rather than playing functionally
• Fascination with spinning wheels, fans, or specific objects
• Extreme distress at changes in routine
• Unusual sensory seeking (e.g., sniffing objects, staring at lights)

Regression (~30% of cases): [12]

• Loss of previously acquired words or social engagement, typically between 15-24 months
• May be gradual or abrupt
• Requires investigation for Rett syndrome (in females), Landau-Kleffner syndrome (epileptic aphasia), or neurometabolic disorder

Preschool (3-5 years)

• Language delay or atypical language (echolalia, pronoun reversal, pedantic speech)
• Difficulty with peer relationships (plays alone, parallel play persists beyond typical age)
• Rigid adherence to routines; meltdowns with changes
• Intense, narrow interests (e.g., letters, numbers, maps)
• Sensory sensitivities become more apparent (covering ears, avoidance of certain foods/textures)

School Age (5-12 years)

• Social difficulties become more prominent as peer relationships become more complex
• Difficulty understanding unwritten social rules, sarcasm, metaphor
• May be bullied or socially isolated
• Academic difficulties despite adequate intelligence (executive function, reading comprehension of inferences)
• Anxiety, particularly social anxiety
• Girls may begin to "camouflage" (mask autistic traits by imitating peers)

Adolescence and Adulthood

• Increasing awareness of social differences may lead to anxiety, depression, low self-esteem
• Some individuals develop coping strategies and improve socially
• Transition to adulthood challenging (employment, independent living, relationships)
• Late-diagnosed individuals (especially females) may present with:
  • Mental health difficulties (anxiety, depression, eating disorders)
  • Relationship difficulties
  • Employment challenges despite good qualifications
  • Retrospective recognition of lifelong social challenges

Gender Differences in Presentation

Clinical Pearl: The Female Autism Phenotype: [6]

Females with ASD are often diagnosed later or missed entirely due to:

1. Camouflaging (Masking): Conscious or unconscious imitation of neurotypical social behaviour

   • Forcing eye contact, rehearsing social scripts, mimicking peers
   • Exhausting and associated with mental health difficulties
   • May "pass" in structured settings (school) but struggle in unstructured social situations

2. Different Restricted Interests:

   • May have more "socially acceptable" interests (animals, celebrities, literature) that are less easily recognised as atypical
   • Interests may be intense but content overlaps with neurotypical peers

3. Better Social Motivation:

   • More desire for friendships, even if lacking skills to maintain them
   • May have one or two close friends (often also neurodiverse or younger)

4. Internalising Symptoms:

   • More likely to present with anxiety, depression, eating disorders than externalising behaviours
   • Higher rates of self-harm

5. Diagnostic Overshadowing:

   • May be misdiagnosed with social anxiety, borderline personality disorder, eating disorder before ASD is considered

Clinical Implication: Maintain high index of suspicion for ASD in females with social anxiety, peer relationship difficulties, eating disorders, or self-harm, particularly if social difficulties have been lifelong.

---

5. Clinical Examination

Developmental and Behavioural Observation

Setting: Observe the child in a naturalistic or semi-structured play setting, ideally with parent/carer and with toys available.

Specific Examination Manoeuvres

1. Joint Attention Testing: [13]

• Distal pointing: Examiner points across room and says, "Oh look!" while making eye contact with child.
  • "Typical: Child follows point, looks at object, then looks back at examiner (triadic gaze)"
  • "ASD: Child may not follow point, or looks at object but does not reference back to examiner"

2. Symbolic Play:

• Offer toys with potential for symbolic play (doll, toy cup, block).
  • Typical: Pretends to drink from cup, feed doll, use block as car ("vroom")
  • "ASD: Uses toys in repetitive or sensory manner (spins wheels, lines up, mouths)"

3. Response to Prohibition:

• Examiner reaches for preferred toy and says "No" with clear affect.
  • "Typical: Child monitors examiner's face for cues, may look distressed or stop"
  • "ASD: May not reference examiner's face; continues regardless"

Physical Examination

General Inspection:

• Dysmorphic features: Suggest syndromic ASD (Fragile X: long face, large ears, macro-orchidism; Tuberous sclerosis: ash-leaf macules, shagreen patches, facial angiofibromas)
• Head circumference: Plot on growth chart (20% of children with ASD have macrocephaly) [17]
• Skin:
  • Café-au-lait spots, axillary freckling (neurofibromatosis type 1)
  • Ash-leaf macules, shagreen patches (tuberous sclerosis complex)
• Neurological examination: Generally normal unless comorbid intellectual disability or cerebral palsy

Essential:

• Hearing assessment: Mandatory to exclude hearing impairment, which can mimic or co-occur with ASD

Red Flags Requiring Urgent Investigation

---

6. Investigations

Screening Tools

Exam Detail: | Tool | Age Range | Setting | Sensitivity/Specificity | Notes | |------|-----------|---------|------------------------|-------| | M-CHAT-R/F (Modified Checklist for Autism in Toddlers, Revised with Follow-up) | 16-30 months | Primary care | Sens 85%, Spec 99% [19] | 20-item parent questionnaire; positive screen requires follow-up interview | | SACS-R (Social Attention and Communication Surveillance-Revised) | 12-24 months | Well-child checks | Sens 83%, Spec 99% | Clinician observation during routine care | | CAST (Childhood Autism Spectrum Test) | 4-11 years | School, primary care | Sens 100%, Spec 97% | 37-item parent questionnaire; useful for school-age children | | AQ-10 (Autism Spectrum Quotient, 10-item) | Adults | Primary care, psychiatry | Sens 88%, Spec 91% | Brief adult screening tool |

Screening Recommendations:

• AAP (American Academy of Pediatrics): Universal ASD screening at 18 and 24 months [19]
• NICE (UK): No universal screening; screen if concerns raised by parent/professional

Diagnostic Assessment Tools

Gold Standard: ADOS-2 (Autism Diagnostic Observation Schedule, 2nd Edition) [13]

• Semi-structured, standardised observational assessment
• Administered by trained clinician (requires certification)
• 5 modules based on language level (Module T for toddlers, Modules 1-4 for older children/adults)
• Assesses communication, social interaction, play, repetitive behaviours
• Generates algorithm score; does NOT diagnose independently (clinical judgment required)
• Duration: 40-60 minutes

ADI-R (Autism Diagnostic Interview-Revised)

• Semi-structured parent/carer interview
• Covers early development, language/communication, social development, repetitive behaviours
• Focuses on behaviour at age 4-5 years and currently
• Duration: 1.5-3 hours
• Useful for gathering developmental history, particularly if regression suspected

Clinical Diagnosis:

• ASD is a clinical diagnosis made by multidisciplinary team based on:
  • Detailed developmental history (parent/carer interview)
  • Direct observation (ADOS-2 or clinical observation)
  • Collateral information (school, nursery)
  • Exclusion of differential diagnoses
• No single test is diagnostic (including ADOS-2)

Additional Investigations

Exam Detail: | Investigation | Indication | Yield/Notes | |---------------|-----------|-------------| | Hearing assessment (audiometry) | All children referred for ASD assessment | Mandatory; excludes hearing impairment | | Vision assessment | All children (baseline) | Excludes visual impairment | | Chromosomal microarray (CMA) | All children diagnosed with ASD | 10% diagnostic yield (detects CNVs) [20] | | Fragile X testing (FMR1) | Males with ASD + ID; family history | 1-2% yield in ASD; higher in ASD + ID | | MECP2 sequencing | Females with ASD + regression | Rett syndrome (typically excluded if "classic ASD" phenotype) | | PTEN testing | Macrocephaly (HC 97th percentile) + ASD | PTEN hamartoma tumour syndrome | | Whole exome sequencing (WES) | ASD + ID + dysmorphism; ASD + consanguinity | 10-30% diagnostic yield in selected populations [20] | | MRI brain | Focal neurological signs, regression, macrocephaly, seizures | NOT routine; only if specific indication | | EEG | Seizures, regression, suspicion of Landau-Kleffner syndrome | NOT routine; only if clinical indication | | Metabolic screen | Regression, encephalopathy, unusual features | Very low yield unless specific clinical suspicion |

NICE Guidance on Investigations: [21]

• Routine metabolic/neuroimaging NOT recommended unless clinical indication
• Genetic testing (CMA) recommended for all children with ASD
• Hearing and vision testing mandatory

Differential Diagnosis and Comorbidity Assessment

Standardised Assessments for Comorbidities:

• Intellectual disability: WISC-V (Wechsler Intelligence Scale for Children), Stanford-Binet
• ADHD: Conners' Rating Scales, ADHD Rating Scale-IV
• Adaptive functioning: Vineland Adaptive Behavior Scales-3 (VABS-3)
• Anxiety/depression: RCADS (Revised Child Anxiety and Depression Scale)
• Sensory processing: Sensory Profile-2

---

7. Differential Diagnosis

Key Differentials

Exam Detail: | Condition | Overlapping Features | Distinguishing Features | |-----------|---------------------|------------------------| | Specific Language Impairment (Developmental Language Disorder) | Delayed language, communication difficulties | Social communication appropriate for language level; no restricted/repetitive behaviours; good nonverbal communication (gestures, eye contact) | | Intellectual Disability (ID) | Developmental delay, language delay, adaptive difficulties | Social communication and play at level expected for mental age (not below); no restricted interests/stereotypies beyond what is typical for developmental level | | Social (Pragmatic) Communication Disorder | Pragmatic language deficits, social difficulties | No restricted/repetitive behaviours (criterion B); DSM-5: cannot be diagnosed if ASD criteria met | | Selective Mutism | Failure to speak in social situations | Speaks fluently in familiar settings (home); anxiety-driven; responds nonverbally; no other ASD features | | ADHD | Inattention, impulsivity, social difficulties | Social difficulties secondary to impulsivity/inattention; can read social cues when attending; no restricted interests/repetitive behaviours | | Hearing Impairment | Language delay, reduced response to name, social difficulties | Responds to visual cues; hearing test abnormal; no restricted/repetitive behaviours | | Rett Syndrome | Regression, hand stereotypies, social difficulties | Females only; normal development until 6-18 months, then regression; hand-wringing/hand-washing stereotypies; deceleration of head growth; MECP2 mutation | | Childhood Disintegrative Disorder (now subsumed into ASD) | Regression after age 2 | Severe regression in multiple domains after ≥2 years normal development; extremely rare | | Attachment Disorder (Reactive Attachment Disorder) | Social difficulties, reduced reciprocity | Clear history of severe neglect/institutional care; may improve with stable caregiving; emotionally withdrawn; no restricted/repetitive behaviours | | Anxiety Disorders (Social Anxiety) | Avoidance of social situations, reduced eye contact | Anxiety-driven; wants social relationships; normal social cognition; situational (not pervasive); no restricted/repetitive behaviours | | Obsessive-Compulsive Disorder (OCD) | Repetitive behaviours, rigidity | Obsessions distressing (ego-dystonic); compulsions performed to reduce anxiety; insight often present; onset typically later (school age/adolescence) |

Important: ASD frequently co-occurs with ID, ADHD, anxiety, and language disorders. These are not mutually exclusive diagnoses.

Syndromic ASD

Approximately 10% of individuals with ASD have an identifiable genetic syndrome. [20]

---

8. Management

Principles of Management

There is NO cure for ASD and NO medication for core social communication deficits. Management focuses on:

1. Early intensive behavioural and developmental interventions
2. Speech and language therapy
3. Educational support (individualised plans)
4. Treatment of comorbidities (ADHD, anxiety, sleep, GI)
5. Family support and psychoeducation
6. Transition planning (to adulthood, employment, independence)

Clinical Pearl: "Early Intervention Is Critical": Meta-analyses demonstrate that initiation of intensive behavioural interventions before age 3-4 years is associated with significantly better outcomes in cognitive ability, language, and adaptive behaviour. [9] The "critical window" for neural plasticity is real.

Early Intensive Behavioural Interventions (EIBI)

Exam Detail: | Intervention | Type | Evidence | Intensity | Key Features | |--------------|------|----------|-----------|--------------| | Early Start Denver Model (ESDM) [9] | Naturalistic developmental behavioural intervention (NDBI) | RCT evidence (Dawson et al., 2010): improved IQ, adaptive behaviour at 2 years | 15-25 hrs/week | Play-based, naturalistic, developmentally focused; parent involvement; targets social communication, imitation, joint attention | | Applied Behaviour Analysis (ABA) | Structured behavioural therapy based on learning theory | Systematic reviews support efficacy for specific skills | 25-40 hrs/week (intensive Lovaas model) | Discrete trial training (DTT); task analysis; positive reinforcement; data-driven; criticism: historical focus on compliance over autonomy | | Pivotal Response Treatment (PRT) | Naturalistic ABA derivative | Evidence from multiple small RCTs | 10-25 hrs/week | Child-initiated; natural reinforcers; targets "pivotal" areas (motivation, responsivity, self-management, initiation) | | JASPER (Joint Attention, Symbolic Play, Engagement, Regulation) | NDBI focused on joint attention and play | RCT evidence for improvements in joint engagement | 2-3 sessions/week (less intensive) | Therapist and parent-mediated; play-based | | PECS (Picture Exchange Communication System) | Augmentative and alternative communication (AAC) | Evidence for communication initiation in non-verbal children | Integrated into daily routine | Teaches functional communication using pictures; 6 phases from requesting to commenting |

Systematic Review Evidence: [9]

• EIBI is associated with moderate-large improvements in cognitive ability (mean IQ gain ~15 points) and adaptive behaviour
• Greatest gains in children starting before age 4 years
• More intensive interventions (≥25 hrs/week) show larger effect sizes
• Parent-mediated interventions cost-effective and show good outcomes

NICE Recommendations: [21]

• Offer intensive, individualised, manualised, psychosocial intervention (≥15 hours/week)
• Should address core deficits in social communication, social interaction, and behaviour
• Parent/carer involvement essential

Speech and Language Therapy (SALT)

Goals:

• Develop functional communication (verbal or non-verbal)
• Improve receptive and expressive language
• Enhance pragmatic/social communication skills
• Teach alternative communication strategies (AAC) if non-verbal

Approaches:

• Augmentative and Alternative Communication (AAC): PECS, sign language (Makaton), speech-generating devices
• Social Communication Interventions: Social Stories™, Comic Strip Conversations, Social Skills Groups
• Pragmatic Language Therapy: Teaching conversation skills, topic maintenance, understanding nonverbal cues

Occupational Therapy (OT)

Focuses on:

• Sensory integration therapy: For hyper-/hypo-sensitivity to sensory stimuli
• Adaptive skills: Dressing, feeding, toileting, fine motor skills
• Sensory diets: Individualised activities to meet sensory needs (e.g., weighted blankets, fidget toys, movement breaks)

Evidence: Sensory-based interventions widely used but limited high-quality RCT evidence. May benefit individual children.

Educational Support

UK: Education, Health and Care Plan (EHCP)

• Statutory document outlining child's needs and support required
• Legally binding; reviewed annually
• May support mainstream placement with additional resources or specialist ASD school

Classroom Strategies:

• Visual supports: Visual timetables, task boards, social stories
• Structured environment: Predictable routines, clear expectations
• Quiet/sensory space: For regulation when overwhelmed
• Differentiated instruction: Adapted to learning style
• Peer support: Buddy systems, social skills groups

Pharmacological Management

Exam Detail: No medication treats core ASD symptoms (social communication, restricted/repetitive behaviours). Medication is only for comorbidities or severe challenging behaviours unresponsive to behavioural interventions. [10]

1. ADHD

NICE: Methylphenidate first-line for ADHD in ASD (same as neurotypical ADHD). [21]

2. Irritability, Aggression, Self-Injury

NICE: Antipsychotics only if severe challenging behaviour unresponsive to psychosocial interventions AND risk to self/others. Use lowest effective dose, time-limited trial, close monitoring. [21]

Clinical Pearl: Always attempt behavioural intervention (functional behaviour analysis, positive behaviour support) before considering antipsychotics.

3. Anxiety

NICE: SSRIs only if severe anxiety unresponsive to psychological therapy. [21]

4. Sleep Disorders

NICE: Melatonin first-line for persistent sleep problems in ASD (after addressing sleep hygiene). [21]

Management Algorithm

┌────────────────────────────────────────────────────────────────┐
│          AUTISM SPECTRUM DISORDER (ASD) MANAGEMENT             │
├────────────────────────────────────────────────────────────────┤
│                                                                │
│  DIAGNOSIS CONFIRMED (multidisciplinary assessment)            │
│                 ↓                                              │
│  ┌──────────────────────────────────────────────────────┐    │
│  │ CORE INTERVENTIONS (All children)                    │    │
│  │  • Early intensive behavioural intervention (EIBI)   │    │
│  │    (ESDM, ABA, PRT) — 15-25 hrs/week if less than 5 years     │    │
│  │  • Speech and Language Therapy (SALT)                │    │
│  │  • Occupational Therapy (sensory, adaptive skills)   │    │
│  │  • Educational support (EHCP, individualised plan)   │    │
│  │  • Parent training and psychoeducation               │    │
│  │  • AAC if non-verbal (PECS, sign, devices)           │    │
│  └──────────────────────────────────────────────────────┘    │
│                 ↓                                              │
│  ASSESS AND TREAT COMORBIDITIES                                │
│  ┌──────────────────────────────────────────────────────┐    │
│  │ ADHD (50%)                                           │    │
│  │  • Behavioural strategies first                      │    │
│  │  • Methylphenidate if significant impairment         │    │
│  │  • Monitor for side effects (higher rate in ASD)     │    │
│  │                                                       │    │
│  │ Anxiety (40%)                                         │    │
│  │  • Adapted CBT (if verbal, sufficient insight)       │    │
│  │  • SSRI (sertraline) if severe, unresponsive          │    │
│  │                                                       │    │
│  │ Sleep disorders (50-80%)                              │    │
│  │  • Sleep hygiene education                           │    │
│  │  • Melatonin 2-10mg at bedtime                       │    │
│  │                                                       │    │
│  │ Epilepsy (20-30%)                                     │    │
│  │  • Standard anti-epileptic treatment                 │    │
│  │  • Neurology referral                                │    │
│  │                                                       │    │
│  │ GI symptoms (40-70%)                                  │    │
│  │  • Assess constipation, reflux, food selectivity     │    │
│  │  • Standard GI management (laxatives, dietary)       │    │
│  └──────────────────────────────────────────────────────┘    │
│                 ↓                                              │
│  SEVERE CHALLENGING BEHAVIOUR (aggression, self-injury)?       │
│                 ↓                                              │
│         NO ←───────────→ YES                                   │
│         ↓                ↓                                     │
│    Continue core    1. Functional Behaviour Analysis (FBA)    │
│    interventions    2. Positive Behaviour Support (PBS)       │
│    Monitor          3. Address triggers (pain, anxiety,       │
│    progress            sensory, communication frustration)    │
│                     4. If severe, unresponsive, risk to       │
│                        self/others:                           │
│                        • Risperidone 0.5-3mg/day (specialist) │
│                        • Aripiprazole 5-15mg/day (specialist) │
│                        • Lowest dose, time-limited trial      │
│                        • Monitor: weight, metabolic, EPS      │
│                                                                │
│  ┌──────────────────────────────────────────────────────┐    │
│  │ TRANSITION TO ADULTHOOD (from age 14+)               │    │
│  │  • Transition planning (education, employment)       │    │
│  │  • Independent living skills training               │    │
│  │  • Transfer to adult services (psychiatry, LD)      │    │
│  │  • Vocational support, supported employment          │    │
│  │  • Mental health monitoring (↑ anxiety, depression)  │    │
│  └──────────────────────────────────────────────────────┘    │
│                                                                │
│  FAMILY SUPPORT (Throughout)                                   │
│  • Parent support groups (National Autistic Society)          │
│  • Respite care                                                │
│  • Siblings support                                            │
│  • Financial support (Disability Living Allowance)            │
│                                                                │
└────────────────────────────────────────────────────────────────┘

Complementary and Alternative Therapies

Common but UNPROVEN therapies:

• Gluten-free, casein-free (GFCF) diet: No evidence of benefit in systematic reviews
• Secretin: No evidence (multiple RCTs negative)
• Hyperbaric oxygen therapy: No evidence
• Chelation therapy: Dangerous; no benefit; risk of death
• Bleach enemas ("Miracle Mineral Solution"): Dangerous; no benefit; harmful

NICE: Do NOT offer these therapies. [21]

---

9. Complications and Prognosis

Complications

Prognosis

Outcomes are highly heterogeneous. Strongest predictors of good long-term outcome:

1. Higher intellectual ability (IQ 70)
2. Development of functional language (by age 5-6 years)
3. Early intensive intervention (before age 3-4 years)
4. Less severe core symptoms (DSM-5 Level 1 vs. Level 3)

Exam Detail: #### Long-Term Outcome Studies

Childhood Outcomes (Systematic Review, 2012):

• ~50% achieve functional language by school age
• 30% achieve "good" outcomes (independent, employed, relationships)
• 50% achieve "fair" outcomes (some independence, require support)
• 20% achieve "poor" outcomes (require substantial lifelong support)

Adult Outcomes:

• ~10-20% live independently without support
• ~20-30% live with some support (supported employment, assisted living)
• ~50-60% require substantial or very substantial support
• Mental health difficulties common (anxiety, depression) in verbally fluent adults with ASD
• Unemployment/underemployment very high (~80%)

Prognostic Factors for Independence:

Quality of Life

• Autistic adults report lower quality of life compared to general population, driven by:

  • Lack of understanding and acceptance ("double empathy problem")
  • Sensory overwhelm in neurotypical-designed environments
  • Social isolation
  • Mental health difficulties
  • Unemployment/underemployment

• Neurodiversity movement emphasises ASD as a difference (not defect), advocates for societal acceptance, accommodations, and identity-first language ("autistic person" vs. "person with autism")

---

10. Prevention and Early Identification

Primary Prevention

No established primary prevention for ASD (given strong genetic basis and unclear environmental triggers).

Prenatal Counselling:

• Advise against valproate in women of childbearing potential unless no alternative (due to teratogenicity and ASD risk) [16]
• Optimise maternal health (folic acid, avoid infections, diabetes control)

Early Identification and Screening

Rationale: Earlier diagnosis enables earlier intervention, which improves outcomes. [9]

Universal Developmental Surveillance

Recommended (AAP, 2020): [19]

• Developmental screening at 9, 18, and 30 months
• ASD-specific screening at 18 and 24 months using M-CHAT-R/F
• Screen if ANY parental/professional concern

Red Flags for Urgent Referral

By 12 months:

• No babbling, pointing, or gestures
• No response to name

By 16 months:

• No single words

By 24 months:

• No two-word meaningful phrases (not echolalia)
• Loss of any language or social skills (regression)

At any age:

• No social smile or shared enjoyment
• Lack of joint attention (pointing to share interest, following point)
• Lack of pretend play
• Repetitive behaviours or intense preoccupations

NICE: Refer to autism assessment team if concerns. [21]

---

11. Examination Focus (Viva Voce and OSCE)

Exam Detail: ### Common Viva Questions and Model Answers

Q1: "What are the DSM-5 diagnostic criteria for Autism Spectrum Disorder?"

Model Answer: "DSM-5 requires both domain A and domain B, plus criteria C, D, and E.

Domain A is persistent deficits in social communication and social interaction across multiple contexts, evidenced by all three of:

1. Deficits in social-emotional reciprocity (e.g., abnormal back-and-forth conversation, reduced sharing of interests)
2. Deficits in nonverbal communication (e.g., poor eye contact, limited gestures)
3. Deficits in developing and maintaining relationships (e.g., difficulty making friends, absence of interest in peers)

Domain B is restricted, repetitive patterns of behaviour, interests, or activities, evidenced by at least two of:

1. Stereotyped or repetitive movements, speech, or use of objects
2. Insistence on sameness, inflexible routines, ritualised patterns
3. Highly restricted, fixated interests abnormal in intensity or focus
4. Hyper- or hypo-reactivity to sensory input

Criterion C: Symptoms present in early developmental period (though may not fully manifest until social demands exceed capacities).

Criterion D: Symptoms cause clinically significant impairment.

Criterion E: Not better explained by intellectual disability or global developmental delay."

---

Q2: "How does the female phenotype of autism differ, and why is this clinically important?"

Model Answer: "Females with ASD are often diagnosed later or missed entirely due to several factors:

1. Camouflaging: Females are more likely to mask autistic traits by consciously imitating neurotypical social behaviours, forcing eye contact, and rehearsing social scripts. This is exhausting and associated with mental health difficulties.

2. Different restricted interests: Females may have interests that are more 'socially acceptable' (e.g., animals, celebrities) and thus less easily recognised as atypical.

3. Better social motivation: Females often have a stronger desire for friendships, even if they lack the skills to maintain them, and may have one or two close friends (often also neurodiverse).

4. Internalising symptoms: Females are more likely to present with anxiety, depression, or eating disorders rather than externalising behaviours.

This is clinically important because it leads to delayed or missed diagnosis, resulting in lack of support and higher rates of mental health difficulties. Clinicians should maintain a high index of suspicion for ASD in females with social anxiety, peer relationship difficulties, or eating disorders, particularly if these have been lifelong."

---

Q3: "What is the evidence for early intensive behavioural interventions in autism?"

Model Answer: "There is good RCT and systematic review evidence that early intensive behavioural interventions (EIBI) improve outcomes in ASD.

Key evidence:

• Early Start Denver Model (ESDM): The landmark RCT by Dawson et al. (2010) randomised toddlers with ASD to 20 hours/week of ESDM vs. community interventions. At 2 years, the ESDM group showed significant improvements in IQ (mean gain ~15 points), adaptive behaviour, and language.

• Systematic reviews: Multiple meta-analyses support EIBI for improving cognitive ability, language, and adaptive behaviour, with moderate-to-large effect sizes. Greatest gains are seen when intervention starts before age 3-4 years and is intensive (≥15-25 hours/week).

• Naturalistic Developmental Behavioural Interventions (NDBIs) like ESDM and JASPER are increasingly preferred over traditional discrete trial ABA due to better generalisation and child engagement.

NICE recommends offering intensive, individualised, manualised psychosocial interventions (≥15 hours/week) with parent involvement for young children with ASD."

---

Q4: "When would you consider pharmacological treatment in a child with ASD, and what are the options?"

Model Answer: "There is no medication for core ASD symptoms (social communication deficits). Medication is reserved for comorbidities or severe challenging behaviours unresponsive to behavioural interventions.

1. ADHD (affects ~50% of children with ASD):

• Methylphenidate is first-line, as per NICE guidance. It has similar efficacy to ADHD without ASD, but higher rates of side effects (irritability, insomnia, appetite suppression). Start low (5mg BD) and titrate slowly.

2. Irritability, aggression, self-injury:

• First, conduct a functional behaviour analysis and implement positive behaviour support to identify and address triggers (pain, anxiety, communication frustration, sensory overload).
• Risperidone and aripiprazole are FDA-approved for irritability in ASD and have RCT evidence (RUPP Autism Network studies). However, they carry significant risks: weight gain, sedation, hyperprolactinaemia, metabolic syndrome, extrapyramidal symptoms. Reserve for severe aggression or self-injury when there is risk to the child or others, and use the lowest effective dose with close monitoring.

3. Anxiety:

• Adapted CBT is first-line for verbal children with sufficient insight.
• SSRIs (sertraline) may be considered if severe and unresponsive to psychological therapy, but monitor for behavioural activation.

4. Sleep disorders:

• Sleep hygiene first, then melatonin 2-10mg at bedtime (good RCT evidence for insomnia in ASD).

NICE emphasises that antipsychotics should only be used if severe challenging behaviour is unresponsive to psychosocial interventions AND poses risk to self or others."

---

Q5: "A mother asks whether the MMR vaccine causes autism. How do you respond?"

Model Answer: "I would reassure the mother that the MMR vaccine does NOT cause autism. This is based on extensive, high-quality evidence:

1. The original Wakefield study (1998, Lancet) claiming a link between MMR and autism was fraudulent and has been retracted. Wakefield had undisclosed conflicts of interest and manipulated data. He was struck off the medical register.

2. Multiple large epidemiological studies (total n 1 million children) have found no association between MMR vaccination and autism. For example, a Danish study of over 650,000 children (Hviid et al., 2019) found no increased risk, even in high-risk subgroups.

3. The rise in autism diagnoses is due to broadened diagnostic criteria (DSM-5), improved awareness, and better identification of subtler cases—not an increase in true incidence.

4. MMR protects against measles, mumps, and rubella, which can cause serious complications including encephalitis, deafness, and death.

I would encourage the mother to vaccinate her child according to the recommended schedule. If she has further concerns, I'd offer time to discuss them and provide written information from reputable sources like NHS or WHO."

---

OSCE Scenario: Developmental Assessment for ASD

Station Brief: You are a paediatric registrar in a developmental clinic. You are seeing Tom, a 2.5-year-old boy, referred by his GP because his parents are concerned about his development. His 18-month M-CHAT-R was positive. Assess Tom for possible autism spectrum disorder.

Key Tasks:

1. Developmental history (from parent):

   • Language milestones (babbling, first words, phrases)
   • Social milestones (social smile, joint attention, pointing, response to name)
   • Play (functional, symbolic, imaginative)
   • Restricted/repetitive behaviours (stereotypies, routines, interests)
   • Regression (loss of skills)

2. Observational assessment (of child):

   • Eye contact
   • Response to name
   • Joint attention (follow point, share interest)
   • Pointing (protodeclarative vs. protoimperative)
   • Play (quality: repetitive vs. symbolic)
   • Social reciprocity (engagement with examiner)

3. Red flags to elicit:

   • By 12 months: no babbling, no gestures, no response to name
   • By 16 months: no words
   • By 24 months: no two-word phrases
   • Regression

4. Explain next steps:

   • Multidisciplinary assessment (paediatrician, psychologist, SALT)
   • ADOS-2 (gold standard observational assessment)
   • Hearing test (mandatory)
   • Genetic testing (chromosomal microarray) if diagnosis confirmed
   • Early intervention (referral to speech therapy, early years support)

Common Pitfalls:

• Forgetting to assess hearing (mandatory before ASD diagnosis)
• Diagnosing based on ADOS-2 alone (it's an assessment tool, not a diagnostic test)
• Not assessing for regression (important red flag)
• Failing to offer early intervention referral even before formal diagnosis

---

12. Patient and Layperson Explanation

What is Autism Spectrum Disorder (ASD)?

Autism Spectrum Disorder (ASD) is a lifelong condition that affects how a person communicates, interacts with others, and experiences the world. It's called a "spectrum" because autism affects people in different ways—some people need a lot of support in daily life, while others live independently but may find social situations challenging.

What are the signs of autism?

Social communication and interaction difficulties:

• Difficulty making friends or understanding social rules (like taking turns in conversation)
• Not responding to their name or avoiding eye contact
• Difficulty understanding facial expressions, tone of voice, or body language
• Preferring to play alone rather than with other children

Restricted and repetitive behaviours:

• Repetitive movements like hand flapping, rocking, or spinning
• Needing routines and getting very upset if things change
• Very intense interests in specific topics (like trains, dinosaurs, or numbers)
• Sensitivity to sounds, lights, textures, or tastes (some children cover their ears at loud noises or refuse to wear certain clothes)

When do signs appear?

Most children with autism show signs before age 3, though some children (especially girls) may not be diagnosed until they are older. Some children develop normally at first and then lose skills like language or social interaction (called "regression").

What causes autism?

Autism is mainly genetic (runs in families) and is present from birth, even if signs aren't obvious immediately. It's caused by differences in how the brain develops, involving hundreds of genes.

Important: Vaccines do NOT cause autism. The study that claimed this was fraudulent and has been completely disproven by many large, high-quality studies.

Some other factors that may slightly increase risk include being born very premature, older parental age, or certain medications during pregnancy (like valproate for epilepsy). However, in most cases, we don't know the exact cause.

How is autism diagnosed?

There is no blood test or scan for autism. Diagnosis is made by a team of specialists (paediatrician, psychologist, speech therapist) who:

• Talk to parents about the child's development
• Observe the child playing and interacting
• Use standardised assessments like the ADOS-2
• Check hearing and vision (to rule out other causes)

Is there a cure?

There is no cure for autism, and many autistic people don't want to be "cured"—they see autism as part of who they are. However, early support and therapy can make a big difference in helping children communicate, learn, and manage daily life.

What treatments are available?

Early intervention therapies (starting before age 3 if possible):

• Speech and language therapy: Helps with communication (speaking, understanding, using pictures or signs if non-verbal)
• Behavioural therapy: Teaches skills like playing, sharing, and following instructions
• Occupational therapy: Helps with daily skills (dressing, eating) and managing sensory sensitivities

Educational support:

• Individualised learning plans at school
• Visual timetables and structured routines
• Extra help in class or specialist schools

Medication (only for specific problems, NOT for autism itself):

• Sleep problems: melatonin
• Anxiety: therapy (and sometimes medication if severe)
• ADHD (common in autism): methylphenidate (Ritalin)

What about "alternative" treatments?

Some treatments you may hear about (like special diets, vitamins, or "detox" therapies) have no scientific evidence and may be harmful or a waste of money. Stick to evidence-based therapies recommended by your child's doctors.

What is the outlook?

Autism is lifelong, but outcomes vary hugely:

• Some autistic people live independently, have successful careers, and form relationships
• Others need lifelong support
• Early intensive therapy, higher intelligence, and developing language by age 5 are the best predictors of independence

Mental health is important—many autistic teenagers and adults experience anxiety or depression, so ongoing support is crucial.

Where can I find support?

• National Autistic Society (UK): www.autism.org.uk
• Autistic Self Advocacy Network (ASAN): Advocacy and information from autistic people
• Parent support groups: Many local groups exist for sharing experiences and advice
• Your child's school/nursery: Can provide educational support and referrals

Key Messages

✅ Autism is a difference in how the brain works, not a disease
✅ Early support improves outcomes
✅ Vaccines do NOT cause autism
✅ Every autistic person is different
✅ Many autistic people lead fulfilling lives with the right support and understanding

---

13. References

Primary Guidelines

1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). Arlington, VA: American Psychiatric Publishing; 2013.

2. Lord C, Elsabbagh M, Baird G, Veenstra-Vanderweele J. Autism spectrum disorder. Lancet. 2018;392(10146):508-520. doi:10.1016/S0140-6736(18)31129-2. PMID: 30078460.

3. Baio J, Wiggins L, Christensen DL, et al. Prevalence of autism spectrum disorder among children aged 8 years — Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2014. MMWR Surveill Summ. 2018;67(6):1-23. doi:10.15585/mmwr.ss6706a1. PMID: 29701730.

4. Maenner MJ, Warren Z, Williams AR, et al. Prevalence and characteristics of autism spectrum disorder among children aged 8 years — Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2020. MMWR Surveill Summ. 2023;72(2):1-14. doi:10.15585/mmwr.ss7202a1. PMID: 36952288.

5. Zeidan J, Fombonne E, Scorah J, et al. Global prevalence of autism: a systematic review update. Autism Res. 2022;15(5):778-790. doi:10.1002/aur.2696. PMID: 35238171.

6. Loomes R, Hull L, Mandy WPL. What is the male-to-female ratio in autism spectrum disorder? A systematic review and meta-analysis. J Am Acad Child Adolesc Psychiatry. 2017;56(6):466-474. doi:10.1016/j.jaac.2017.03.013. PMID: 28545751.

7. Grove J, Ripke S, Als TD, et al. Identification of common genetic risk variants for autism spectrum disorder. Nat Genet. 2019;51(3):431-444. doi:10.1038/s41588-019-0344-8. PMID: 30804558.

8. Taylor LE, Swerdfeger AL, Eslick GD. Vaccines are not associated with autism: an evidence-based meta-analysis of case-control and cohort studies. Vaccine. 2014;32(29):3623-3629. doi:10.1016/j.vaccine.2014.04.085. PMID: 24814559.

9. Fuller EA, Kaiser AP. The effects of early intervention on social communication outcomes for children with autism spectrum disorder: a meta-analysis. J Autism Dev Disord. 2020;50(5):1683-1700. doi:10.1007/s10803-019-03927-z. PMID: 30796695.

10. Howes OD, Rogdaki M, Findon JL, et al. Autism spectrum disorder: consensus guidelines on assessment, treatment and research from the British Association for Psychopharmacology. J Psychopharmacol. 2018;32(1):3-29. doi:10.1177/0269881117741766. PMID: 29237330.

11. Lai MC, Kassee C, Besney R, et al. Prevalence of co-occurring mental health diagnoses in the autism population: a systematic review and meta-analysis. Lancet Psychiatry. 2019;6(10):819-829. doi:10.1016/S2215-0366(19)30289-5. PMID: 31447415.

12. Barger BD, Campbell JM, McDonough JD. Prevalence and onset of regression within autism spectrum disorders: a meta-analytic review. J Autism Dev Disord. 2013;43(4):817-828. doi:10.1007/s10803-012-1621-x. PMID: 22855372.

13. Lord C, Rutter M, DiLavore PC, Risi S, Gotham K, Bishop SL. Autism Diagnostic Observation Schedule, 2nd Edition (ADOS-2). Torrance, CA: Western Psychological Services; 2012.

14. Brugha TS, McManus S, Bankart J, et al. Epidemiology of autism spectrum disorders in adults in the community in England. Arch Gen Psychiatry. 2011;68(5):459-465. doi:10.1001/archgenpsychiatry.2011.38. PMID: 21536975.

15. Tick B, Bolton P, Happé F, Rutter M, Rijsdijk F. Heritability of autism spectrum disorders: a meta-analysis of twin studies. J Child Psychol Psychiatry. 2016;57(5):585-595. doi:10.1111/jcpp.12499. PMID: 26709141.

16. Christensen J, Grønborg TK, Sørensen MJ, et al. Prenatal valproate exposure and risk of autism spectrum disorders and childhood autism. JAMA. 2013;309(16):1696-1703. doi:10.1001/jama.2013.2270. PMID: 23613074.

17. Sacco R, Gabriele S, Persico AM. Head circumference and brain size in autism spectrum disorder: a systematic review and meta-analysis. Psychiatry Res. 2015;234(2):239-251. doi:10.1016/j.pscychresns.2015.08.016. PMID: 26456415.

18. Rubenstein JL, Merzenich MM. Model of autism: increased ratio of excitation/inhibition in key neural systems. Genes Brain Behav. 2003;2(5):255-267. doi:10.1034/j.1601-183x.2003.00037.x. PMID: 14606691.

19. Hyman SL, Levy SE, Myers SM; Council on Children with Disabilities, Section on Developmental and Behavioral Pediatrics. Identification, evaluation, and management of children with autism spectrum disorder. Pediatrics. 2020;145(1):e20193447. doi:10.1542/peds.2019-3447. PMID: 31843864.

20. Schaefer GB, Mendelsohn NJ; Professional Practice and Guidelines Committee. Clinical genetics evaluation in identifying the etiology of autism spectrum disorders: 2013 guideline revisions. Genet Med. 2013;15(5):399-407. doi:10.1038/gim.2013.32. PMID: 23519317.

21. National Institute for Health and Care Excellence. Autism spectrum disorder in under 19 s: support and management (CG170). 2013 (updated 2021). Available at: https://www.nice.org.uk/guidance/cg170

22. Hirvikoski T, Mittendorfer-Rutz E, Boman M, Larsson H, Lichtenstein P, Bölte S. Premature mortality in autism spectrum disorder. Br J Psychiatry. 2016;208(3):232-238. doi:10.1192/bjp.bp.114.160192. PMID: 26541693.

---

END OF DOCUMENT