7.4 Developmental & Behavioral Disorders

Developmental & Behavioral Disorders

This section covers three of the highest-yield behavioral and developmental topics on the exam: autism spectrum disorder (ASD) red flags and screening, the core diagnostic features of attention-deficit/hyperactivity disorder (ADHD), and the distinction between global developmental delay (GDD) and intellectual disability (ID).

Autism Spectrum Disorder (ASD)

ASD is a neurodevelopmental disorder defined, per the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, Text Revision (DSM-5-TR), by two core symptom clusters that must both be present, beginning in the early developmental period:

1. Persistent deficits in social communication and social interaction across multiple contexts — deficits in social-emotional reciprocity, deficits in nonverbal communicative behaviors used for social interaction such as eye contact, gestures, and facial expression, and deficits in developing, maintaining, and understanding relationships.
2. Restricted, repetitive patterns of behavior, interests, or activities — at least 2 of: stereotyped or repetitive motor movements or speech; insistence on sameness or inflexible adherence to routines; highly restricted, fixated interests of abnormal intensity; and hyper- or hypo-reactivity to sensory input, such as an extreme reaction to specific sounds or textures.

Red Flags Warranting Autism-Specific Evaluation

Regression, most classically noted between 18 and 24 months, is the single most concerning historical finding for ASD and should never be dismissed as a phase.

Screening

The American Academy of Pediatrics (AAP) recommends universal autism-specific screening at the 18-month and 24-month well-child visits, in addition to general developmental screening at 9, 18, and 30 months. The standard tool is the Modified Checklist for Autism in Toddlers, Revised, with Follow-Up (M-CHAT-R/F), a 20-item parent-report questionnaire validated for children 16-30 months of age.

Scoring:

• 0-2 points, low risk — no further action needed unless a red flag is noted on exam or history
• 3-7 points, medium risk — administer the structured M-CHAT-R/F follow-up interview items; refer for diagnostic evaluation and early intervention if the child remains positive
• 8 points or higher, high risk — skip the follow-up interview and refer directly for diagnostic evaluation and early intervention services

A positive screen is not a diagnosis — it triggers referral for comprehensive diagnostic evaluation, but early intervention services should be initiated in parallel rather than delayed pending formal diagnosis.

Attention-Deficit/Hyperactivity Disorder (ADHD)

ADHD's DSM-5-TR criteria are built from two symptom domains, each listing 9 possible items: inattention, for example careless mistakes, difficulty sustaining attention, not listening, losing things, being easily distracted, and forgetfulness, and hyperactivity-impulsivity, for example fidgeting, leaving one's seat, running or climbing excessively, difficulty waiting one's turn, and interrupting.

Core diagnostic requirements:

• 6 or more symptoms from either or both domains for children under 17 years; 5 or more symptoms required for adolescents 17 and older and adults
• Symptoms present for at least 6 months, to a degree inconsistent with developmental level
• Several symptoms present before age 12, the DSM-5 age-of-onset threshold, raised from age 7 in DSM-IV
• Symptoms present in at least 2 settings, such as home and school — a child who is disruptive only at home, or only at school, does not meet criteria
• Clear evidence that symptoms interfere with or reduce the quality of social, academic, or occupational functioning
• Not better explained by another mental disorder

Presentations: predominantly inattentive, predominantly hyperactive-impulsive, or combined.

Evaluation: the AAP recommends formal ADHD evaluation for any child 4-18 years presenting with academic or behavioral concerns consistent with inattention, hyperactivity, or impulsivity. Diagnosis requires validated rating scales, such as the Vanderbilt or Conners scales, completed by informants in at least 2 settings, typically parent and teacher, and mimics must be excluded — hearing or vision impairment, sleep disorders, learning disabilities, anxiety, mood disorders, and absence seizures can all present with inattentive or seemingly hyperactive behavior.

First-line management (AAP): for children 4-5 years, parent training in behavior management is first-line, with medication reserved for moderate-to-severe impairment that persists despite behavioral intervention. For children 6 years and older, FDA-approved medication, with stimulants as first-line, combined with behavior therapy is recommended.

Global Developmental Delay vs. Intellectual Disability

Global developmental delay (GDD) is the term applied to children under 5 years with a significant delay, generally defined as performance 2 or more standard deviations below the age-expected mean, in at least 2 developmental domains: gross motor, fine motor, speech/language, cognition, social/personal, and activities of daily living. GDD is a descriptive term used in young children because formal, standardized IQ testing is not reliable before this age.

Intellectual disability (ID), the DSM-5 term that replaced mental retardation, is typically diagnosed at 5 years or older, once standardized testing is feasible, and requires both:

1. Deficits in intellectual functioning, such as reasoning, problem-solving, and abstract thinking, confirmed by standardized testing, approximately IQ 70 or below, roughly 2 SD below the mean, and
2. Deficits in adaptive functioning across conceptual, social, and practical domains that limit independent functioning at the expected level for age and culture

Onset must occur during the developmental period. Severity in DSM-5 is graded as mild, moderate, severe, or profound based primarily on adaptive functioning, not IQ score alone, a key change from earlier editions. Not every child with GDD goes on to meet criteria for ID; some catch up, which is exactly why the more provisional term GDD is preferred before age 5.

Etiologic workup for GDD/ID: detailed prenatal, perinatal, and family history; examination for dysmorphic features; chromosomal microarray (CMA) as the first-tier genetic test, offering the highest diagnostic yield; Fragile X testing when there is a suggestive family history or physical features such as macroorchidism, a long face, or large ears; brain MRI when focal neurologic signs, an abnormal head circumference, or regression are present; and targeted metabolic testing when regression, consanguinity, or specific red flags suggest an inborn error of metabolism.