To be diagnosed with mental retardation, symptoms must be present in childhood. Adults who experience a loss in cognitive functioning may be diagnosed with another illness such as dementia. A number of factors can cause mental retardation, including:

• Down Syndrome and fetal alcohol syndrome significantly increase a person’s risk of mental retardation, though not all people with these conditions have mental retardation.
• Improper development during pregnancy can contribute to the development of symptoms, and exposure to certain drugs in utero—particularly illegal drugs and alcohol—greatly increases a fetus’ risk of being born with mental retardation.
• Illness and infection that affect the brain may lead to the condition, and very high fevers in early childhood can cause mental retardation. Measles and meningitis may also contribute to the development of mental retardation.