63.2 Autism Spectrum Disorder & Intellectual Disabilities

Autism Spectrum Disorder (ASD)

Autism Spectrum Disorder (ASD) is a heterogeneous neurodevelopmental disorder characterized by persistent impairments in social communication and interaction paired with restricted, repetitive patterns of behavior, interests, or sensory activities. In the United States, ASD affects approximately 1 in 36 children, with a male-to-female ratio of approximately 4:1. However, females with ASD are frequently diagnosed later in life or overlooked entirely due to higher social motivation and advanced behavioral camouflaging ('masking').

Neurobiology & Etiology

The etiology of ASD is complex and predominantly genetic, with heritability estimates exceeding 80%:

• Polygenic Architecture: Hundreds of common and rare genetic loci converge on pathways governing synaptogenesis, dendritic spine architecture, neuronal migration, and synaptic plasticity.
• Brain Growth Trajectory: A subset of children with ASD (15-20%) exhibit abnormal early brain growth, characterized by accelerated head circumference expansion and macrocephaly between 6 and 14 months of age, followed by premature deceleration of brain growth in later childhood.
• Neural Connectivity: Functional neuroimaging demonstrates local hyper-connectivity within isolated cortical circuits paired with long-range hypo-connectivity between distributed brain networks (e.g., fronto-striatal and fronto-temporal tracts), impeding complex social cognition, executive processing, and multisensory integration.

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DSM-5 Diagnostic Criteria for ASD

A formal DSM-5 diagnosis requires persistent deficits across both core domains (Criterion A and Criterion B):

                    DSM-5 DIAGNOSTIC CRITERIA FOR ASD

   Domain & Criteria         Mandatory Requirements & Clinical Manifestations
   ══════════════════════════════════════════════════════════════════════════════════════════════════════
   Criterion A               Persistent deficits in social communication and social interaction
   (Social Communication     across multiple contexts (MUST MEET ALL 3):
   & Interaction)            1. 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.
                             2. Deficits in nonverbal communicative behaviors:
                                • Poorly integrated verbal and nonverbal communication.
                                • Abnormalities in eye contact, body language, or deficits in understanding gestures.
                                • Total absence of facial expressions or nonverbal gestures.
                             3. Deficits in developing, maintaining, and understanding relationships:
                                • Difficulties adjusting behavior to suit diverse social contexts.
                                • Difficulties in sharing imaginative play or making friends.
                                • Absence of interest in peers.
   ──────────────────────────────────────────────────────────────────────────────────────────────────────
   Criterion B               Restricted, repetitive patterns of behavior, interests, or activities
   (Restricted / Repetitive  (MUST MEET AT LEAST 2 OF THE FOLLOWING 4):
   Behaviors & Sensory)      1. Stereotyped or repetitive motor movements, use of objects, or speech:
                                • Hand flapping, finger flicking, body rocking, spinning.
                                • Lining up toys, flipping objects repetitively.
                                • Echolalia (immediate or delayed), idiosyncratic phrases.
                             2. Insistence on sameness, inflexible adherence to routines, or ritualized patterns:
                                • Extreme distress at small changes in routine or environment.
                                • Difficulties with transitions; rigid thinking patterns.
                                • Ritualized greeting patterns, needing to take exact same route or eat same food.
                             3. Highly restricted, fixated interests abnormal in intensity or focus:
                                • Strong attachment to or preoccupation with unusual objects (e.g., vacuum cleaners).
                                • Excessively circumscribed or perseverative special interests.
                             4. Hyper- or hyporeactivity to sensory input or unusual sensory interests:
                                • Apparent indifference to pain or extreme temperatures.
                                • Adverse, extreme reactions to specific sounds, textures, or smells.
                                • Excessive smelling or touching of objects; visual fascination with lights/spinners.
   ──────────────────────────────────────────────────────────────────────────────────────────────────────
   Criterion C               Symptoms must be present in the early developmental period (though may
   (Developmental Timing)    manifest fully later when social demands exceed capacities or masked by learned strategies).
   ──────────────────────────────────────────────────────────────────────────────────────────────────────
   Criterion D               Symptoms cause clinically significant impairment in social, occupational,
   (Functional Impairment)   or other vital areas of current functioning.
   ──────────────────────────────────────────────────────────────────────────────────────────────────────
   Criterion E               Disturbances are not better explained by intellectual disability or global
   (Exclusion / Comorbidity) developmental delay (note: ID and ASD frequently co-occur).
   ══════════════════════════════════════════════════════════════════════════════════════════════════════

Severity Specifiers for ASD

Severity is classified separately for Social Communication and Restricted/Repetitive Behaviors:

• Level 1: 'Requiring support': Noticeable impairments without supports; difficulty initiating social interactions; atypical or unsuccessful responses to social overtures; ritualized inflexibility interferes with functioning in one or more contexts.
• Level 2: 'Requiring substantial support': Marked deficits in verbal and nonverbal social communication; social impairments apparent even with supports; limited initiation; simple sentences; distress or difficulty coping with change.
• Level 3: 'Requiring very substantial support': Severe deficits in verbal and nonverbal skills causing severe functional impairment; very few words of intelligible speech; minimal response to social overtures; extreme difficulty coping with change; repetitive behaviors severely interfere with daily life.

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Developmental Surveillance & Universal Screening (AAP Guidelines)

The American Academy of Pediatrics (AAP) establishes explicit guidelines separating continuous developmental surveillance from standardized screening:

1. Continuous Developmental Surveillance: Recommended at every well-child encounter from birth through adolescence, including eliciting parental concerns, documenting developmental milestones, and clinical observation.
2. General Standardized Developmental Screening: Administered using validated tools (e.g., Ages & Stages Questionnaires [ASQ-3], Parents' Evaluation of Developmental Status [PEDS]) at 9, 18, and 30 months of age.
3. Dedicated Universal ASD Screening: Administered to all children at 18 months AND 24 months of age (and at any visit when a parent or clinician raises concerns).

                  THE M-CHAT-R/F SCREENING & TRIAGE ALGORITHM

   Total Score Range    Risk Stratification    Immediate Clinical Action Required
   ══════════════════════════════════════════════════════════════════════════════════════════════════════
   Score 0 - 2          Low Risk               • Negative screen.
                                               • If child is <24 months, rescreen at 24-month well-child visit.
                                               • Continue routine developmental surveillance.
   ──────────────────────────────────────────────────────────────────────────────────────────────────────
   Score 3 - 7          Medium Risk            • Administer the structured M-CHAT-R/F Follow-Up Interview.
                                               • If Follow-Up score remains ≥2: Positive screen -> Refer for
                                                 comprehensive evaluation & Part C early intervention.
                                               • If Follow-Up score is 0-1: Screen negative -> Routine surveillance.
   ──────────────────────────────────────────────────────────────────────────────────────────────────────
   Score 8 - 20         High Risk              • Screen HIGH POSITIVE.
                                               • BYPASS the Follow-Up Interview!
                                               • IMMEDIATELY refer for comprehensive multidisciplinary
                                                 developmental evaluation AND refer directly to state-funded
                                                 Part C Early Intervention services.
   ══════════════════════════════════════════════════════════════════════════════════════════════════════

Critical Early Red Flags for ASD ('Rules of Thumb')

Family physicians must recognize milestone absences that warrant prompt diagnostic referral rather than passive 'wait-and-see' reassurance:

• By 6 Months: No social smiles or warm, joyful facial expressions directed at caregivers; lack of sustained eye contact.
• By 9 Months: No back-and-forth sharing of vocal sounds, smiles, laughter, or facial expressions.
• By 12 Months: Lack of reciprocal babbling; failure to respond to name (often mistaken for deafness); absence of communicative gestures (pointing, showing, reaching, waving goodbye).
• By 16 Months: Complete absence of spoken single words.
• By 24 Months: Complete absence of spontaneous, meaningful two-word phrases (excluding immediate echolalia or rote repetition).
• AT ANY AGE: ANY loss of previously acquired speech, babbling, or social engagement! Developmental regression occurs in approximately 20% to 30% of children with ASD, typically between 15 and 24 months of age, and represents a red-flag indication for urgent multidisciplinary evaluation.

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Comprehensive Diagnostic Evaluation Workup

When an infant or toddler screens positive or displays red flags, the family physician must coordinate a multidisciplinary evaluation:

1. Formal Audiology Evaluation: Mandatory standardized audiometry to exclude conductive or sensorineural hearing loss as a primary driver of language delay.
2. Multidisciplinary Developmental Assessment: Comprehensive evaluation utilizing gold-standard standardized diagnostic instruments (Autism Diagnostic Observation Schedule-2 [ADOS-2] and Autism Diagnostic Interview-Revised [ADI-R]) administered by a developmental pediatrician, child psychologist, or pediatric neurologist.
3. First-Line Genetic Testing: Chromosomal Microarray (CMA) and Fragile X DNA analysis (FMR1 CGG trinucleotide repeat expansion) are recommended first-line investigations. Whole-exome sequencing (WES) is increasingly utilized if CMA is non-diagnostic.
4. Neurological & Metabolic Testing: Routine brain MRI and routine EEG are not recommended unless the child exhibits focal neurological deficits, microcephaly, macrocephaly, tuberous sclerosis stigmas (ash-leaf spots), or clinical unprovoked seizures.

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Evidence-Based Interventions for ASD

1. Non-Pharmacologic Early Intervention (First-Line Standard of Care)

Neuroplasticity is maximal in early childhood; early initiation of intensive behavioral and developmental therapies yields dramatic gains in IQ, language, and adaptive living scores:

• Applied Behavior Analysis (ABA): The gold-standard intensive behavioral therapy (typically 20-40 hours per week). ABA breaks complex communicative, social, and functional living skills down into discrete, manageable steps, utilizing systematic positive reinforcement to build adaptive behaviors and reduce maladaptive behaviors.
• Speech and Language Therapy: Initiated early to develop pragmatic communication skills; for nonverbal children, early introduction of Augmentative and Alternative Communication (AAC) systems (e.g., Picture Exchange Communication System [PECS] or speech-generating tablet devices) fosters functional language and prevents behavioral frustration.
• Occupational Therapy: Focuses on sensory integration therapies, fine motor coordination, and self-care activities of daily living.
• Educational Support: Mandated federal support via the Individuals with Disabilities Education Act (IDEA): an Individualized Family Service Plan (IFSP) under Part C (birth to age 3) transitioning to an Individualized Education Program (IEP) under Part B (ages 3 to 21).

2. Pharmacotherapy for Target Symptoms in ASD

[!IMPORTANT] Pharmacotherapy does NOT treat core social communication deficits or repetitive behaviors in ASD. Prescription medications are strictly reserved for severe, functionally impairing target symptoms refractory to behavioral interventions: extreme irritability, physical aggression, severe temper tantrums, and self-injurious behavior (SIB).

                  FDA-APPROVED ATYPICAL ANTIPSYCHOTICS FOR ASD TARGET SYMPTOMS

   Agent          FDA Age Range    Initial & Target Dosing           Key Adverse Effects & Monitoring
   ══════════════════════════════════════════════════════════════════════════════════════════════════════
   Risperidone    Ages 5 - 16      Weight <20 kg: Start 0.25 mg/day  • Severe weight gain & metabolic syndrome
                  years            Weight ≥20 kg: Start 0.5 mg/day   • Hyperprolactinemia (galactorrhea, gynecomastia)
                                   Target: 1.0 - 2.5 mg/day          • Somnolence, sedation, tremor
                                   (Max: 3.0 mg/day)                 • EPS and Tardive Dyskinesia risk
   ──────────────────────────────────────────────────────────────────────────────────────────────────────
   Aripiprazole   Ages 6 - 17      Start: 2 mg orally daily          • Weight gain (less than risperidone)
                  years            Titrate by 2-5 mg weekly          • Akathisia (motor restlessness, agitation)
                                   Target: 5 - 10 mg/day             • Somnolence, insomnia, nausea
                                   (Max: 15 mg/day)                  • EPS and Tardive Dyskinesia risk
   ══════════════════════════════════════════════════════════════════════════════════════════════════════

• Mandatory Safety & Metabolic Monitoring Protocol:
  • Baseline: Body weight, height, BMI, blood pressure, fasting plasma glucose or HbA1c, and fasting lipid profile.
  • At 3 Months: Repeat BMI, blood pressure, fasting glucose, and fasting lipid panel.
  • Annually: Fasting glucose/HbA1c and lipid panel.
  • Every Encounter: Clinical surveillance for extrapyramidal symptoms (EPS), akathisia, and involuntary motor movements utilizing the Abnormal Involuntary Movement Scale (AIMS).
• Comorbid ADHD in ASD: Approximately 30-50% of children with ASD have comorbid ADHD. Stimulants (methylphenidate) and non-stimulants (guanfacine, atomoxetine) are effective; however, children with ASD experience higher rates of adverse effects (irritability, emotional lability, insomnia) from psychostimulants than neurotypical children, warranting cautious low-dose titration.

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Intellectual Disability (Intellectual Developmental Disorder)

Intellectual Disability is a lifelong neurodevelopmental disorder defined by concurrent deficits in cognitive abilities and adaptive functioning with onset during the developmental period.

DSM-5 Diagnostic Criteria

Diagnosis requires meeting all three core criteria:

1. Deficits in Intellectual Functions: Reasoning, problem-solving, planning, abstract thinking, judgment, academic learning, and experiential learning. Confirmed through clinical evaluation and standardized, individualized cognitive testing yielding an IQ score of approximately 70 or below (representing ≥2 standard deviations below the population mean of 100, accounting for a 5-point measurement error margin: 65 to 75).
2. Deficits in Adaptive Functioning: Failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, adaptive deficits limit functioning in one or more activities of daily life across three adaptive domains:
   • Conceptual Domain: Competence in language, reading, writing, mathematics, reasoning, knowledge, and memory.
   • Social Domain: Empathy, interpersonal communication, social judgment, friendship abilities, and awareness of others' thoughts and feelings.
   • Practical Domain: Self-management across life settings, including personal care, job responsibilities, money management, recreation, transportation, and organizing school or work tasks.
3. Developmental Onset: Onset of intellectual and adaptive deficits occurs during the developmental period (before age 18).

               ADAPTIVE FUNCTIONING SEVERITY TIERS IN INTELLECTUAL DISABILITY

   Severity Level   Conceptual Domain                  Social Domain                  Practical Domain
   ══════════════════════════════════════════════════════════════════════════════════════════════════════════
   Mild             Difficulties learning academic     Immature social interactions;  Independent personal care;
   (~85% of ID)     skills (reading, math); abstract   gullibility; risk of being     requires support for complex
                    thinking impaired in adults.        manipulated by peers.          tasks (money, legal, taxes).
   ──────────────────────────────────────────────────────────────────────────────────────────────────
   Moderate         Markedly behind peers; academic    Simple spoken language;        Can care for personal needs
   (~10% of ID)     skills at elementary level;        interprets social cues poorly; with extended teaching;
                    requires daily assistance.         support needed for friendships. semi-independent group living.
   ──────────────────────────────────────────────────────────────────────────────────────────────────
   Severe           Limited conceptual attainment;     Spoken language very limited;  Requires support for all
   (~3-5% of ID)    little understanding of written    communicates via single words  daily living activities;
                    language or numeric concepts.      or gestures; focused on here.  cannot live independently.
   ──────────────────────────────────────────────────────────────────────────────────────────────────
   Profound         Concepts involve physical world    Very limited understanding of  Dependent on caregivers for
   (~1-2% of ID)    rather than symbolic processes;    symbolic communication;        all aspects of daily physical
                    co-occurring motor/sensory deficits. expresses desires nonverbally. care, health, and safety.
   ══════════════════════════════════════════════════════════════════════════════════════════════════════════

Exam Pearl: Under DSM-5, the severity of Intellectual Disability is determined by the level of adaptive functioning, NOT by the IQ score, because adaptive functioning determines the actual level of environmental support required.

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Etiologic Classifications

• Genetic Etiologies:
  • Down Syndrome (Trisomy 21): Most common genetic cause of ID. Associated with characteristic facies, hypotonia, congenital heart defects (atrioventricular septal defects), early-onset Alzheimer neuropathology by age 40, celiac disease, hypothyroidism, and atlantoaxial instability.
  • Fragile X Syndrome: Most common inherited cause of intellectual disability in males. Caused by an unstable CGG trinucleotide repeat expansion (>200 repeats) in the FMR1 gene on the X chromosome leading to transcriptional silencing. Phenotype includes long, narrow face, prominent jaw, large everted ears, joint hypermobility, macroorchidism post-puberty, and high rates of co-occurring ASD.
  • Rett Syndrome: X-linked dominant mutation in the MECP2 gene, primarily affecting females. Features normal early development followed by rapid regression of purposeful hand skills and expressive language, replaced by stereotypic hand-wringing or hand-washing movements, microcephaly, breathing irregularities, and ataxia.
• Metabolic & Environmental Etiologies:
  • Inborn Errors of Metabolism: Phenylketonuria (PKU; screened at birth), galactosemia, Wilson disease.
  • Fetal Alcohol Spectrum Disorder (FASD): Leading preventable cause of ID. Cardinal facial dysmorphisms: smooth philtrum, thin vermilion border of upper lip, short palpebral fissures, paired with microcephaly and severe behavioral deficits.
  • Congenital Infections (TORCH): Cytomegalovirus (CMV; periventricular calcifications, sensorineural hearing loss), Toxoplasmosis (chorioretinitis, hydrocephalus, diffuse intracranial calcifications), Rubella, Congenital Syphilis.
  • Perinatal & Postnatal Insults: Hypoxic-ischemic encephalopathy, kernicterus, extreme prematurity, bacterial meningitis, traumatic brain injury, and chronic lead neurotoxicity.

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Primary Care Health Maintenance for Adults with Intellectual Disabilities

1. Communication & Legal Decision-Making Capacity

• Address the patient directly using clear, concrete language, visual aids, and extra processing time, while also engaging caregivers or group home staff for collateral information.
• Assess legal decision-making capacity. Differentiate between independent decision-making, supported decision-making agreements, healthcare power of attorney, and formal court-appointed legal guardianship. Consent for invasive procedures or pharmacotherapy must be obtained from the legally recognized surrogate if guardianship is documented.

2. Eliminating Cancer Screening Disparities

• Adults with intellectual disabilities face pervasive health disparities and are frequently denied evidence-based preventive screenings:
  • Cervical Cancer Screening: Regular Pap smears and HPV testing must be maintained per USPSTF guidelines. Desensitization, pre-visit clinic tours, and gentle pelvic examinations (or sedation if strictly necessary) should be offered rather than arbitrarily omitting screening.
  • Colorectal Cancer Screening: Screening from ages 45 to 75 must be prioritized. If immobility or sensory defensiveness precludes colonoscopy preparation, non-invasive stool-based testing (FIT or stool DNA-FIT) should be deployed.

3. Dental Care & Bone Health

• Dental Disease: High incidence of untreated periodontal disease, caries, and tooth loss due to poor manual dexterity, medication-induced xerostomia, and sensory aversion. Biannual specialized dental cleanings are required.
• Bone Health: Markedly elevated risk of premature osteoporosis and fragility fractures driven by immobility, low dietary calcium/vitamin D, and chronic treatment with enzyme-inducing antiepileptic drugs (e.g., phenytoin, carbamazepine, phenobarbital) that induce CYP3A4 and accelerate 25-hydroxyvitamin D catabolism. Clinicians must monitor 25-OH vitamin D levels, optimize calcium supplementation, and obtain baseline DEXA scans in high-risk patients.

4. The Critical Danger of 'Diagnostic Overshadowing'

[!CAUTION] Diagnostic Overshadowing is the cognitive bias wherein a healthcare provider erroneously attributes new, emerging, or worsening behavioral symptoms (such as agitation, screaming, aggression, pacing, or self-injurious head-banging) to the patient's baseline intellectual disability or autism, rather than investigating an acute, treatable medical illness.

Individuals with severe cognitive and expressive communication deficits cannot verbalize pain. When experiencing acute physical distress, they express discomfort through behavioral agitation. Whenever an adult with intellectual disability presents with a sudden behavioral change, the family physician must perform a systematic physical examination and laboratory workup to rule out occult physical sources of pain before escalating behavioral medications:

1. Dental Abscess: Impacted third molars or periapical dental infection.
2. Severe Constipation / Fecal Impaction: Palpable lower-quadrant abdominal mass, stercoral ulceration.
3. Urinary Tract Infection (UTI): Cystitis, pyelonephritis, urinary retention.
4. Gastroesophageal Reflux Disease (GERD): Esophagitis, peptic ulceration (often presenting as mealtime aggression).
5. Occult Orthopedic Fractures: Undetected fall fractures (especially femoral neck or ribs).
6. Acute Otitis Media or Corneal Abrasion: Ear canal foreign body, cerumen impaction, eye scratching.