Intellectual Disability

(Cognitive Disability; Developmental Disability; Mental Retardation)


Intellectual disability begins in childhood. People with intellectual disability have limits in their mental functioning seen in below-average intelligence (IQ) tests and in their ability to communicate, socialize, and take care of their everyday needs. The degree of disability can vary from person to person. It can be categorized as mild, moderate, severe, or profound.


Several hundred causes of intellectual disability have been discovered, but many are still unknown. The most common ones are:
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Risk Factors

A child could be at higher risk for intellectual disability due to any of the causes listed above, or due to intellectual disability in other family members. If you are concerned that your child is at risk, tell your child's doctor.


Symptoms appear before a child reaches age 18. Symptoms vary depending on the degree of the intellectual disability. If you think your child has any of these symptoms, do not assume it is due to intellectual disability. These symptoms may be caused by other, less serious health conditions.
Symptoms include:
The following categories are often used to describe the level of intellectual disability:


  • IQ 50-70
  • Slower than normal in all areas
  • No unusual physical signs
  • Can learn practical skills
  • Reading and math skills up to grades 3-6
  • Can conform socially
  • Can learn daily task skills
  • Functions in society


  • IQ 35-49
  • Noticeable delays, particularly speech
  • May have unusual physical signs
  • Can learn simple communication
  • Can learn elementary health and safety skills
  • Can participate in simple activities and self-care
  • Can perform supervised tasks
  • Can travel alone to familiar places


  • IQ 20-34
  • Significant delays in some areas; may walk late
  • Little or no communication skills, but some understanding of speech with some response
  • Can be taught daily routines and repetitive activities
  • May be trained in simple self-care
  • Needs direction and supervision socially


  • IQ <20
  • Significant delays in all areas
  • Congenital abnormalities present
  • Needs close supervision
  • Requires attendant care
  • May respond to regular physical and social activity
  • Not capable of self-care


If you suspect your child is not developing skills on time, tell the doctor as soon as possible. You will be asked about your child’s symptoms and medical history. A physical exam will be done. Standardized tests may be given that measure:
Children with intellectual disability have a higher risk for other disabilities such as hearing impairment, visual problems, seizures, attention deficit hyperactivity disorder, or orthopaedic conditions. Additional testing may be needed to check for other conditions.


Talk with your doctor about the best treatment plan for your child. Treatment is most helpful if it begins as early as possible. Treatment includes:


To help reduce your child’s chance of becoming intellectually disabled, take the following steps:


The Arc

American Association of Intellectual and Developmental Disabilities


Canadian Psychological Association

Special Olympics Canada


Causes and prevention of intellectual disabilities. The Arc website. Available at: Updated March 1, 2011. Accessed November 18, 2015.

Daily D, Ardinger H, et al. Identification and evaluation of mental retardation. Am Fam Physician. 2000;61(4):1059-1067.

Facts about intellectual disability. The Centers for Disease Control and Prevention website. Available at: Accessed November 18, 2015.

Questions and answers about persons with intellectual disabilities in the workplace. US Equal Employment Opportunities Commission website. Available at: Accessed November 18, 2015.

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