Boy wearing toy crown looks at picture book in a classroom

An intellectual disability (ID) can be described as an impairment to cognitive functioning. Intellectual disabilities, which originate before age 18 and are the most common type of developmental disability, may be mild to severe and are characterized by limitations in intellectual functioning and adaptive behavior such as social and practical skills.

In the past, the term mental retardation was used widely to refer to this condition. In 2010, President Obama signed Rosa's Law, a bill that required any instances of "mental retardation" to be gradually replaced with "intellectual disability" and "individual with an intellectual disability" in all federal policy.

Many other agencies followed suit, changing their terminology in response to requests from advocacy organizations that rejected the term "mental retardation" for its negative connotations and potential to generate misunderstanding about an individual's particular condition. The term has now fallen out of general use. By 2013, the Social Security Administration had replaced the term in the Listing of Impairments with the term "intellectual disability."

What Is Intellectual Disability?

Between 1% and 3% of the population have some type of intellectual disability. An intellectual disability may be diagnosed if an individual shows cognitive limitations and experiences limitations to adaptive behavior.

An IQ test score that falls between 70 and 75 is another key indicator of an intellectual disability. Those who are diagnosed with this condition will typically experience some difficulty with general learning and may take longer to develop the skills necessary for everyday function. 

Although there may be some life skills people intellectual disabilities are unable to learn, those diagnosed with an intellectual disability are still often able to attend school, obtain an education, and learn how attend to their personal needs. General learning typically takes longer and requires more repetition, but many people are able to learn the life skills necessary to live independently, such as find and maintain employment.

Intellectual Disability Symptoms and Signs

The fifth edition of the Diagnostic and Statistical Manual (2013) reflects the updated terminology for the condition adopted by many other official agencies. In the DSM, intellectual disability, or intellectual developmental disorder, is described as a condition marked by deficits in intellectual and adaptive functioning:

  • Intellectual functioning includes abstract thinking, planning, ability to solve problems, and capacity for academic learning. 
  • Adaptive functioning includes social skills and ability to work and communicate appropriately with others. It also includes a person’s ability to live on their own and attend to their basic needs.

Some characteristics of intellectual disability in adults could include impaired ability to:

  • Follow rules and obey laws
  • Understand time, money, and other number concepts
  • Care for oneself
  • Safely travel from one place to another
  • Engage with others socially 

In order for these signs to lead to an ID diagnosis, they must be present during childhood or adolescence.

A young girl and her mother smiling at each other

Children and Intellectual Disabilities

A child who is intellectually disabled may reach certain milestones of development later than children who are not similarly affected. For example, a child may stand and walk later than other children of the same age, be unable to see the consequences of actions, lack curiosity, display infant-like behavior past the age of infancy, and have difficulty in school. 

Other characteristics of intellectual disability in children may include: 

  • Deficits in memory skills
  • Delays in oral language development
  • Delays in developing adaptive behaviors such as self-care or self-help
  • Difficulty learning social rules
  • Difficulty with problem-solving skills
  • A lack of social inhibitors

A child diagnosed with an ID may develop and learn at a slower pace than a child who does not have an ID, and it can take the child longer to learn language, self-care skills, and social skills. Intellectually disabled children are often still able to learn and achieve some level of function, especially with the help and support of a trained professional.

Types of Intellectual Disability

At one point, IQ was more heavily relied upon when diagnosing an intellectual disability and determining its severity. While the DSM-5 still recognizes these categories, more emphasis is placed on the skills associated with each level rather than their IQ:

  • Mild: Those with a mild intellectual disability may have an IQ between 50-70. Eighty-five percent of intellectually disabled people are at this level, and they can often live on their own with minimum support from others. 
  • Moderate: The IQ for a moderate intellectual disability can range from 36-49. Those with a moderate intellectual disability make up roughly 10% of cases on this spectrum. These individuals may need more support in day-to-day life and may live in a group home. 
  • Severe: Making up about 3.5% of those with intellectual disabilities, these individuals may fall into the 20-35 IQ range. They typically need daily supervision to keep them healthy and safe and may need help with basic self-care tasks.
  • Profound: Individuals with a profound intellectual disability may have an IQ under 20 and make up only 1.5% of intellectual disability cases. They may need constant care and supervision to meet their basic needs.

Certain conditions may be associated with ID including:

While the conditions listed above are not types of intellectual disabilities, they may cause them.

Causes of Intellectual Disability

Not all causes of intellectual disability are known. In about 75% of all cases diagnosed, doctors are not able to find a specific reason for the disability. Some known causes include:

  • Lack of oxygen at birth, infections or other problems during labor and birth
  • Fetal infection or fetal developmental issues
  • Exposure to toxins such as lead, mercury, and drugs. Fetal alcohol syndrome, which results from intrauterine exposure to alcohol, can also cause intellectual disability. 
  • Diseases such as whooping cough, meningitis, and measles
  • Chromosomal abnormalities. Down syndrome and fragile X syndrome both result from inherited abnormal genes. 
  • Iodine deficiency and malnutrition
  • Trauma to the developing fetus
  • Trauma sustained in infancy or childhood

While there is no cure for intellectual disability, they can be effectively managed. Learn more about treatment options for intellectual disabilities.

References:

  1. Boat, T. F., & Wu, J. T. (2015). Mental disorders and disabilities among low-income children. Washington, D.C.: National Academies Press. 
  2. Change in terminology: 'Mental retardation' to 'intellectual disability' (2013, August 1). Retrieved from https://www.federalregister.gov/articles/2013/08/01/2013-18552/change-in-terminology-mental-retardation-to-intellectual-disability
  3. Diagnostic and statistical manual of mental disorders: DSM-5. (5th ed.). (2013). Washington, D.C.: American Psychiatric Association.
  4. Diament, M. (2010, October 5). Obama signs bill replacing 'mental retardation' with 'intellectual disability.' Retrieved from http://www.disabilityscoop.com/2010/10/05/obama-signs-rosas-law/10547
  5. Harris, J. C. (2013). New terminology for mental retardation in DSM-5 and ICD-11. Current Opinion in Psychiatry, 26(3), 260-262. doi: 10.1097/YCO.0b013e32835fd6fb
  6. Intellectual disability. (2017, June 16). Retrieved from http://www.parentcenterhub.org/repository/intellectual
  7. Intellectual disability. (2013, May 10). Retrieved from https://www.nlm.nih.gov/medlineplus/ency/article/001523.htm
  8. Reynolds, T., Zupanick, C. E., & Dombeck, M. (n.d.). Diagnostic criteria for intellectual disabilities: DSM-5 criteria. Retrieved from https://www.mentalhelp.net/articles/diagnostic-criteria-for-intellectual-disabilities-dsm-5-criteria 
  9. Types of intellectual disabilities. (n.d.). Retrieved from https://www.hwns.com.au/about-us/about-disability/types-of-disabilities/types-of-intellectual-disabilities