Algorithmic approach to the evaluation for causes of intellectual disability in children

CMA: chromosomal microarray analysis; GDD: global developmental delay; CT: computed tomography; ID: intellectual disability; FISH: fluorescence in situ hybridization; MRI: magnetic resonance imaging.
* If the child has not previously had lead screening performed, a blood lead level should be obtained. Lead is the most common environmental neurotoxin, but an uncommon cause of ID in the United States.
¶ Common specific causes of ID include Down syndrome, fragile X syndrome, Rett syndrome, Klinefelter syndrome, Prader-Willi syndrome, DiGeorge syndrome, metabolic disorders, muscular dystrophy, congenital hypothyroidism, and lead poisoning. However, there are many other causes of ID in children. For more details, refer to UpToDate content on ID in children and to UpToDate topics on these specific disorders.
Δ If CMA is unavailable, G-band karyotype and FISH testing are applied.
◊ Many experts recommend fragile X testing in all children with unexplained ID or autism, since fragile X syndrome often presents with non-specific GDD in young children.
§ Consultation with a pediatric neurologist may be warranted in these cases. MRI is the preferred neuroimaging modality; however, CT is acceptable if MRI is not available. Potential radiation exposure and risk of sedation should be considered as part of informed decision making. Some abnormal findings on neuroimaging do not lead to a specific diagnosis. Additional evaluation may be warranted.