is often poorly understood because its effects vary greatly among those who have it. Many people with intellectual disability are mildly affected and may not be identified until later during school years. Individuals with intellectual disability may also have physical, medical, behavioral, psychological, or emotional problems.
People with intellectual disability who have a very low intelligence quotient (IQ) have serious limitations in their ability to function. However, with early intervention and appropriate support, they can also lead satisfying lives. The goal of treating intellectual disability is to help children stay in the family and take part in community life. In the United States, they are guaranteed education and other services.
Intellectual disability usually begins in childhood and is characterized by limitations in both intelligence and adaptive skills. The following 3 criteria must be met for a diagnosis of intellectual disability:
IQ below 75
Significant limitations exist in adaptive behaviors, such as self-care, socializing, and communicating
The disability begins before age 18
Any condition that impairs development of the brain before birth, during birth, or during childhood can cause intellectual disability. The main causes can be categorized as follows:
Genetic abnormalities may be inherited from parents or may be caused by environmental factors.
There are many genetic diseases are associated with intellectual disability. Examples include:
(PKU)—Children born with this rare genetic disorder cannot metabolize phenylalanine (PHE), which is an amino acid found in food. Without proper treatment, PKU can lead to intellectual disability.
Down syndrome—In a normal fertilized egg, chromosomes exist in pairs. But, in the case of Down syndrome, there are 3 of chromosome 21.
Fragile X syndrome—This is caused by mutations of the FMR1 gene, the leading cause of inherited intellectual disability.
by a pregnant mother can cause intellectual disability.
can increase the risk, as well. Other risks during pregnancy include:
MalnutritionCertain environmental toxins such as lead
Illnesses of a mother during pregnancy that can be passed on to her infant, such as:
Toxoplasmosis—an infection caused by a parasite
Cytomegalovirus—caused by the herpes virusRubella—German measlesHIVSyphillisHerpes simplexPreeclampsia
Prescription medications such as
isotretinoin and phenytoin
and low birth weight may sometimes lead to intellectual disability. Other birth complications and conditions or physical stress in the newborn stage may also injure an infant's brain.
The American Association on Intellectual and Developmental Disabilities (AAIDD) has a process for diagnosing and classifying a person with intellectual disability. This process involves assessing the person's IQ and adaptive skills. Adaptive skills fall into 3 categories:
Conceptual skills—For example, can the person read and write? Does he or she understand concepts like time and money?Social skills—Does the person follow rules? Does he or she have interpersonal skills? Can he or she solve social problems?Practical skills—Can the person take care of his daily needs? Can he or she work, use money, and stay safe?
The best assistance for people with intellectual disability begins with diagnosis and help early in life. Treatment includes:
Early interventionSpecial educationFamily supportCase managementJob trainingTransition servicesHousing services
With enough education and support, many people with intellectual disability can learn to take care of their basic needs and to live in the community.
Newborn screening followed by proper treatment can prevent intellectual disability resulting from certain conditions. Examples include:
Phenylketonuria (PKU)Congenital hypothyroidism
Vaccines can prevent certain infectious diseases that may lead to intellectual disability. Women who plan to become pregnant should be current on all recommended vaccinations, such as:
Other interventions that can reduce the risk of intellectual disability include:
Early and comprehensive prenatal care, including prenatal vitamins containing folateAbstaining from alcohol, tobacco, and drugs during pregnancy
Many parents also choose to have certain tests done during pregnancy, including ultrasound, amniocentesis, chorionic villus sampling, and blood tests. These tests cannot prevent intellectual disability, but they can give parents more time to prepare for a child with intellectual disability.
The ARC website. Available at:
http://www.thearc.org/page.aspx?pid=2543. Accessed July 19, 2016.
Children with an intellectual disability. The American Academy of Child and Adolescent Psychiatry website. Available at:
http://www.aacap.org/aacap/Families_and_Youth/Facts_for_Families/Facts_for_Families_Pages/Children_with_an_Intellectual_Disability_23.aspx. Updated October 2013. Accessed July 19, 2016.
Diagnostic adaptive behavior scale. American Association on Intellectual and Developmental Disabilities website. Available at: http://aaidd.org/intellectual-disability/diagnostic-adaptive-behavior-scale. Accessed July 19, 2016.
Free appropriate public education for students with disabilities. US Department of Education website. Available at: http://www2.ed.gov/about/offices/list/ocr/docs/edlite-FAPE504.html. Updated August 2010. Accessed July 19, 2016.
Intellectual disability. National Dissemination Center for Children With Disabilities website. Available at:
http://nichcy.org/disability/specific/intellectual. Updated July 2015. Accessed July 19, 2016.
Intellectual disability. Merck Manual Professional Version website. Available at:
https://www.merckmanuals.com/professional/pediatrics/learning-and-developmental-disorders/intellectual-disability. Updated February 2016. Accessed July 19, 2016.
8/19/2014 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed: Reilly C, Atkinson P, et al. Neurobehavioral comorbidities in children with active epilepsy: a population-based study. Pediatrics. 2014;133(6):e1586-1593.
Last reviewed July 2016 by Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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