Intellectual disability, formerly known as mental retardation, can be caused by injury, disease, or a problem in the brain. For many children, the cause of their intellectual disability is unknown.
Some causes of intellectual disability, such as Down syndrome, Autism Spectrum Disorders, Fragile X syndrome, birth defects, and infections, can happen before birth. Some happen while a baby is being born or soon after birth.
Other causes of intellectual disability do not occur until a child is older; these might include severe head injury, infections or stroke.