Diagnostic Approach to Global Developmental Delay and Intellectual Disability in Pediatrics

Etiology

The American Academy of Child and Adolescent Psychiatry suggests that genetic causes are the most frequent, identifiable through chromosomal microarrays (CGH array) that provide diagnosis in up to 10% of patients with normal karyotype 1
Specific chromosomal anomalies include: 22q11.2 deletion (DiGeorge syndrome) with mild to borderline intellectual disability, Smith-Magenis syndrome (17p11.2 deletion) with moderate intellectual disability, and Lesch-Nyhan syndrome (HPRT deficiency) with mild to moderate intellectual disability 1

For children under 5 years, the term "Global Developmental Delay" should be used instead of intellectual disability, as IQ tests are unreliable in this age group; significant delay (≥2 standard deviations below the mean) in at least two developmental domains (motor, language, social, cognitive) is required 1, 2
For children over 5 years, the diagnosis of intellectual disability requires deficits in both intellectual and adaptive functioning, with onset during the developmental period 3

The American Academy of Pediatrics recommends that a detailed three-generation history and expert physical and neurological examination lead to diagnosis in 40% of cases and are the cornerstone of evaluation 7
The Bayley Scales of Infant and Toddler Development (Third Edition) is the primary recommended tool for comprehensive developmental assessment in children with suspected or confirmed global developmental delay, providing standardized scores in motor and cognitive domains 2

The American Academy of Child and Adolescent Psychiatry suggests that targeted interventions to environmental influences, communication, language, hearing, vision, motor or sensory function, and coexisting medical or psychiatric conditions allow for new skill acquisition and improvement in functioning 3, 5
Early intervention is critical to optimize outcomes, particularly when treatable neuromuscular disorders are identified, where early therapy can improve outcomes 7

The American Academy of Child and Adolescent Psychiatry recommends that sleep disorders in Smith-Magenis syndrome require specific management of the inverted melatonin circadian rhythm 4, 1
Epilepsy treatment can significantly improve functioning 3
Sensory deficits require correction of vision and hearing problems 1

The American Academy of Child and Adolescent Psychiatry suggests using validated measures in children with intellectual disability/global developmental delay when available, such as the Developmental Behaviour Checklist (DBC) and Nisonger Child Behavior Rating Form (NCBRF) 6
Measures developed with typical development samples may not be valid for young people with intellectual disability/global developmental delay 6

The intensity and nature of required supports may change over time; diagnostic assessments should determine whether improved adaptive skills result from stable and generalized acquisition of new skills (in which case the intellectual disability diagnosis may no longer be appropriate) or if improvement depends on the presence of ongoing supports and interventions (in which case the intellectual disability diagnosis remains appropriate) 3, 5