Chapter 19 - Global developmental delay and intellectual disability

Abstract

Global developmental delay (GDD) and intellectual disability (ID) are complementary chronologically framed entities that encapsulate heterogeneous “symptom complexes” that are frequent reasons for pediatric medical evaluation and intervention. GDD is defined as a significant functional delay in two or more developmental domains and is typically applied to children less than 5 years of age. ID is applied to children over 5 years for whom psychometric testing documents significant cognitive limitations together with the observation of deficits in adaptive behavior that requires systems of support to maximize individual participation. The etiology of these disorders, like their presentation and evolution, is quite heterogeneous. It is estimated that one-quarter to one-half of identified causes are genetic in origin. Identification of these genetic causes has furthered our understanding of the molecular basis for learning and memory. While the medical evaluation of these entities is by necessity highly individualized, guidelines exist to assist the practitioner in rationally identifying appropriate screening tests and selecting specific diagnostic tests. Advances in genetic and molecular testing suggest that the standards of evaluation and diagnostic yields will be in a state of considerable flux in the near term.