🧠 Chapter 24: Intellectual and Developmental Disability (IDD)

Nelson's Pediatric Symptom-Based Diagnosis | Global Developmental Delay · ID Diagnostic Criteria · Fragile X · Down Syndrome · Autism · Cerebral Palsy · Hearing/Vision Screening

🔍 Intellectual & Developmental Disability: Key Concepts

📊 Definitions
Intellectual Disability (ID): deficits in intellectual (IQ <70) and adaptive functioning (conceptual, social, practical) with onset <18 years. Global Developmental Delay (GDD): <5 years, significant delay in ≥2 domains. Developmental Disability: broader, includes CP, autism, sensory deficits, epilepsy.
🔄 Diagnostic Criteria (DSM-5)
ID requires: (A) deficits in intellectual functions (reasoning, problem-solving, planning); (B) deficits in adaptive functioning (conceptual, social, practical); (C) onset during developmental period. Severity: mild, moderate, severe, profound.
⚠️ Red Flags for Regression
Loss of milestones (developmental regression) suggests neurodegenerative disorder (Rett, leukodystrophy, metabolic). Urgent evaluation: MRI, metabolic studies, genetic testing.
💧 Common Genetic Causes
Down syndrome (trisomy 21), Fragile X (FMR1, most common inherited ID), 22q11.2 deletion, Prader-Willi/Angelman (15q11.2), Williams (7q11.23). Chromosomal microarray first-tier test.
🧬 Treatable ID (Treatable-ID.org)
Conditions with disease-modifying treatments: PKU, galactosemia, congenital hypothyroidism, Wilson disease, biotinidase deficiency, creatine disorders, B12 deficiency.
🚩 Screening & Surveillance
AAP: developmental surveillance at every visit, standardized screening at 9, 18, 30 months. Parental concern has 74-80% sensitivity. Formal audiology and ophthalmology evaluation.

💡 Key Takeaway: ID is a clinical diagnosis based on intellectual and adaptive deficits. GDD is used in young children. First-tier genetic testing: chromosomal microarray + Fragile X. Metabolic testing if red flags (regression, acidosis, hyperammonemia). Early intervention improves outcomes.

🩺 Clinical Approach to Intellectual/Developmental Disability: Step-by-Step

🔹 Step 1: Determine if delay is isolated or global
• Isolated: single domain (speech, motor) → possible specific disorder.
• Global (≥2 domains) → GDD/ID likely. Use developmental screening tools (ASQ, PEDS).
🔹 Step 2: Identify red flags for treatable/urgent conditions
• Developmental regression (loss of milestones) → neurodegenerative or metabolic.
• Dysmorphic features, organomegaly, coarse facies → storage disease.
• Neonatal seizures, hypotonia, acidosis, hyperammonemia → inborn error of metabolism.
• Microcephaly or macrocephaly → structural or genetic.
🔹 Step 3: Diagnostic workup (tiered approach)
• First-tier: Chromosomal microarray (CMA) + Fragile X DNA testing.
• Second-tier (if negative): Whole exome sequencing, metabolic testing (plasma amino acids, urine organic acids, acylcarnitine, lactate, ammonia).
• Neuroimaging (MRI brain) if macro/microcephaly, focal neuro findings, or seizures.
• Audiology and ophthalmology evaluation.
🔹 Step 4: Evaluate adaptive functioning
• Vineland Adaptive Behavior Scales (standardized). Assess conceptual (academic), social (interpersonal), practical (self-care) domains.
🔹 Step 5: Management & Early Intervention
• Refer to early intervention (Birth-3) or school-based services (3-21).
• Treatable causes: PKU (diet), hypothyroidism (levothyroxine), Wilson (chelation), B12 deficiency.
• Comorbidities: seizures, behavioral issues, constipation, GERD, sleep disorders.