Table 2.

Causes of global developmental delay/intellectual disability

Broad category	Possible causes	Proportion of diagnostic yield*
Prenatal intrinsic	Genetic	Up to 47%
	Central nervous system malformations	Up to 28%
	Metabolic
Prenatal extrinsic	Teratogens/toxins (drugs of abuse, medications, etc.)	Up to 21%
	Infections
Perinatal	Asphyxia	Up to 55%
	Prematurity
	Neonatal complications
Postnatal	Neglect/psychosocial environment	Up to 11%
	Infections
	Trauma
	Toxins

Data taken from ref. (3).

*Percentage of total cases of GDD/ID with an identified etiologic diagnosis who fall into this specific category.