Intellectual Disability

The scope of this page is centralized content about individuals with an intellectual disability (ID) and associated communication difficulties across the life span.


See ASHAs Intellectual Disability evidence map for summaries of the available research on this topic.

Intellectual Disability

The definitions of intellectual disability (ID) and related terminology have evolved over time to reflect the legal and social gains made by individuals with such a disability and their families. See Changes in Services for Persons With Developmental Disabilities: Federal Laws and Philosophical and Perspectives and Federal Programs Supporting Research and Training in Intellectual Disability. These changes reflect the movement from institutionalization to inclusive practices, self-advocacy, and self-determination. There has also been the movement toward recognizing fundamental communication rights of people with severe disabilities. A Communication Bill of Rights—originally developed by the National Joint Committee for the Communication Needs of Persons with Severe Disabilities (NJC) in 1992 and updated in 2016—recognizes the right of all people to effective communication (NJC, 1992; Brady et al., 2016).

One of the major shifts in the early 1980s was a move toward person-first language, reflecting the idea that the disability does not define the person. Terms like individuals with intellectual disability have replaced the older terms of mentally retarded persons or the mentally retarded, and definitions of ID have changed from being strictly intelligence quotient (IQ)–based to including strengths in adaptive behavior (Schalock, Luckasson, & Shorgren, 2007).

ID is characterized by

  • significant limitations in intellectual functioning (e.g., reasoning, learning, and problem solving);
  • significant limitations in adaptive behavior (i.e., conceptual, social, and practical skills in everyday life); and
  • onset in childhood (before the age of 18 years; American Association on Intellectual and Developmental Disabilities [AAIDD, 2013]).

This definition of ID balances limitations with an equal emphasis on skills. Consequently, language and philosophy concerning ID now focuses on levels of support necessary to maximize an individual's ability, rather than strictly on deficits in functioning.

The AAIDD definition is consistent with the diagnostic criteria for Intellectual Disability (Intellectual Developmental Disorder) in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association [APA], 2013). Severity levels (mild, moderate, severe, and profound), as defined in DSM-5, are based on adaptive functioning in the conceptual, social, and practical domains.

Limitations in adaptive functioning in specific skill areas are a necessary criterion for diagnosis under the AAIDD and DSM-5 definitions. The World Health Organizations (WHO, 2001) International Classification of Functioning, Disability and Health (ICF) and the ICF Children and Youth Version (WHO, 2007) recognize activity and participation limitations in addition to impairments in body functions and structures.

Developmental Disability

ID is a subset of developmental disability (DD). DD is defined as follows:

  • A severe, chronic disability in an individual 5 years of age or older
  • Onset before 22 years of age
  • Results in substantial functional limitations in three or more areas of life activity (self-care, receptive and expressive language, learning, mobility, self-direction, capacity for independent learning, economic self-sufficiency 
    (Developmental Disabilities Assistance and Bill of Rights Act, 2000)

Lifelong, early-onset conditions that result in substantial functional limitations—but not necessarily concomitant intellectual limitations—include autism spectrum disorder (ASD) or cerebral palsy (although many individuals with these conditions do, in fact, have ID). Individuals with these diagnoses who have age-level cognitive skills would be considered to have DD without ID.

Co-occurring Conditions and Disorders

Individuals with ID are a heterogeneous group, and communication skills can vary due to factors such as severity, co-occurring conditions, and other behavioral, emotional, and social factors.

Conditions that either commonly co-occur with—or are fully comorbid with—ID include but are not limited to ASD, cerebral palsy, Down syndrome, fetal alcohol syndrome, and Fragile X syndrome. Other conditions that may also co-occur with ID include anxiety disorder, attention-deficit/hyperactivity disorder, depressive and bipolar disorder, impulse-control disorder, and major depressive disorder (APA, 2013). See Communication Characteristics: Selected Populations With an Intellectual Disability for general communication characteristics of individuals with these most common conditions associated with ID.

Associated Health Conditions

Individuals with ID may have more health problems than others in the general population, often as a result of inadequate health care, limited access to quality services (Krahn, Hammond, & Turner, 2006; van Schrojenstein Lantman-de Valk & Noonan Walsh, 2008), and communication limitations (Gentile, Cowan, & Smith, 2015).

Associated health conditions with a higher prevalence in individuals with ID include:

  • anxiety disorders (Oeseburg, Dijkstra, Groothoff, Reijneveld, & Jansen, 2011);
  • hearing loss (Herer, 2012);
  • heart conditions (Patja, Molska, & Iivanainen, 2001);
  • obesity-related problems (Rimmer, Yamaki, Lowry, Wang, & Vogel, 2010);
  • seizure activity (Oeseburg et al., 2011); and
  • visual impairment (Warburg, 2001).

Greater attention could be devoted to special health needs of individuals with disabilities as a regular part of medical training (Sullivan et al., 2011). Addressing health inequalities as well as providing adequate health care and medical training can improve quality of life and increase longevity in individuals with ID.

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