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 (ID) is characterized by

  • onset in the developmental period (before the age of 22 years; American Association on Intellectual and Developmental Disabilities [AAIDD], n.d.);
  • significant limitations in adaptive behavior (i.e., conceptual, social, and practical skills to function in daily life); and
  • significant limitations in intellectual functioning (e.g., learning, reasoning, and problem solving).

This definition of ID balances limitations with an equal emphasis on skills. Descriptive terminology and philosophy concerning ID focuses on levels of support necessary to maximize an individual’s ability, rather than strictly on functional limitations.

Diagnosis of ID is not made by a speech-language pathologist (SLP). However, information gathered during SLP evaluation and treatment may be useful to medical professionals who may diagnose ID. Assessment and treatment of disorders that fall under speech-language pathology scope of practice may be completed at any stage in an individual’s life. Treatment may begin as early as these disorders are detected, and early intervention is critical in identifying and providing services that will support both the child and the family (Guralnick, 2019).

Terminology

The definitions of 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 Perspectives and Federal Programs Supporting Research and Training in Intellectual Disability. These changes reflect the movement away from a “medical model” and institutionalization and toward inclusive practices, self-advocacy, and self-determination. There has also been the movement toward recognizing the fundamental communication rights of people with severe disabilities. The Communication Bill of Rights—originally developed by the National Joint Committee for the Communication Needs of Persons With Severe Disabilities in 1992 and updated in 2016—recognizes the right of all people to participate fully in communication (Brady et al., 2016). For full participation, the Communication Bill of Rights identifies access to functioning augmentative and alternative communication (AAC) and other assistive technology services and devices as necessary at all times.

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. Rosa’s Law, a federal law enacted in 2017, changed all prior references to “mental retardation” in federal law to “intellectual disability” or “intellectual disabilities.” Please see AAIDD’s page on Historical Context for further details. Terminology continues to evolve, with some individuals preferring identity-first language (e.g., “autistic person”). There is also an evolving cultural awareness of ableism (discrimination favoring able-bodied people). The American Speech-Language-Hearing Association (ASHA) aligns with the Disability section of the 7th edition of the American Psychological Association (2020) style manual, which says to use the terminology preferred by the individual. Definitions of ID have changed from being strictly IQ based to including strengths in adaptive behavior (Schalock et al., 2021; Tassé, 2017).

The AAIDD definition is consistent with the diagnostic criteria for Intellectual Disability (Intellectual Developmental Disorder) in the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association [APA], 2013). However, AAIDD identifies the level of ID based on the level of supports needed for an individual to successfully function in activities of daily living. These levels of support are described as intermittent, limited, extensive, or pervasive. The DSM-5 uses severity level to define an individual with ID as mild, moderate, severe, or profound.

Limitations in adaptive functioning in specific skill areas are a necessary criterion for diagnosis under the AAIDD and DSM-5 definitions. The World Health Organization’s (WHO’s) International Classification of Functioning, Disability and Health (ICF) framework (WHO, 2001) and its Children & 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). Per the Institute of Medicine (US) Committee on Nervous System Disorders in Developing Countries (2001), DD is a set of limitations that begin in infancy or childhood, with delays in reaching developmental milestones or limitations in one or more of the following domains:

  • cognition
  • motor performance
  • vision
  • hearing and speech
  • behavior

The Developmental Disabilities Assistance and Bill of Rights Act of 2000 defines or characterizes DD 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 such as
    • self-care,
    • receptive and expressive language,
    • learning,
    • mobility,
    • self-direction,
    • capacity for independent learning, and
    • economic self-sufficiency

Lifelong, early-onset conditions that result in substantial functional limitations—but not necessarily concomitant intellectual limitations—include autism spectrum disorder (ASD) or cerebral palsy. Individuals with these diagnoses who do not have significant limitations in adaptive behavior and intellectual functioning are considered to have DD without ID.

Co-Occurring Conditions and Disorders

Communication skills among individuals with ID can vary due to severity; co-occurring conditions; and other behavioral, emotional, and social factors. Conditions that commonly co-occur with ID include, but are not limited to, the following.

ASD

ASD is a neurologically based, heterogeneous condition, characterized by a range of social communication skills and the presence of restricted, repetitive behaviors, which are present in early childhood. These and other features include the following:

  • Persistent deficits in social communication and social interaction across multiple contexts (e.g., joint attention, social-emotional reciprocity, nonverbal and verbal communication skills, initiation of conversation; APA, 2013).
  • Restricted and repetitive use of language (e.g., echolalia, perseveration; APA, 2013).
  • Delay or absence of spoken communication (D. K. Anderson et al., 2007).
  • Difficulty with abstract language (Tager-Flusberg & Caronna, 2007).
  • Difficulty with narrative discourse (Colle et al., 2008).
  • May have a speech sound disorder (Shriberg et al., 2011).
  • May have feeding problems (Twachtman-Reilly et al., 2008).

Communication delays or limitations in social functioning may signal ASD, ID, or other conditions. A medical practitioner or team may have difficulty making a diagnosis of ID or ASD due to similarities and comorbidity between the two conditions. The SLP’s input may be useful to the medical team when considering comorbidity or differential diagnosis between the two disorders.   

Commonalities between ASD and ID include

  • onset during the developmental period,
  • difficulty with nonverbal communication modalities (e.g., gestural or facial expression),
  • speech patterns (e.g., prosody) as well as receptive and expressive pragmatic and sociolinguistic communication skills,
  • limitations in social participation,
  • attention and academic difficulties, and
  • difficulty with theory of mind (ToM).

Differences between ASD and ID include the following:

  • Individuals with ID have limitations in intellectual functioning and adaptive behavior, whereas individuals with ASD have a wide range of intellectual abilities and adaptive behavior.
  • Individuals with ID usually develop skills slower than their typically developing peers do, whereas individuals with ASD may not follow the typical developmental progression of skills across domains.
  • Individuals with both ASD and ID may have more difficulty with ToM than those with ID alone (Cáceres et al., 2014).

Please see ASHA’s Practice Portal page on Autism Spectrum Disorder for further information. 

Cerebral Palsy

Cerebral palsy is a motor disorder that may affect speech, language, and swallowing. Variable difficulties, depending on the area of the brain affected and the severity, are experienced, which may include the following:

  • Increased risk for language disorders (Pennington et al., 2005).
  • May have hearing loss (Rosenbaum & Rosenbloom, 2012).
  • Dysarthria is the most common speech disorder (McNeil, 2009).
  • Feeding and swallowing may be compromised (Sullivan, 2009).

Down Syndrome

Down syndrome is a genetic syndrome associated with intellectual disability, limitations in adaptive skills, and anatomical differences in tongue size (relative macroglossia). Other characteristics include the following:

  • Language comprehension is better than production, particularly syntax (J. E. Roberts et al., 2007).
  • Speech intelligibility problems, which may result from disturbances in voice, articulation, resonance, fluency, or prosody (Kent & Vorperian, 2013).
  • Stuttering is more prevalent (Eggers & Van Eerdenbrugh, 2018).
  • Persistent otitis media; conductive and sensorineural hearing loss is common (Shott, 2006).
  • Morphosyntax is more difficult than semantics (Fidler et al., 2009), with variability in vocabulary development compared to children with other intellectual disabilities or typical development (Loveall et al., 2016).
  • Social and pragmatic skill strengths that vary depending on executive function and ToM skills (Lee et al., 2017).

Fetal Alcohol Syndrome

Fetal alcohol syndrome is a congenital syndrome resulting from alcohol exposure in utero. It is a leading cause of developmental disabilities in the United States (Clarke & Gibbard, 2003). Characteristics may include the following:

  • Delayed speech and language acquisition (Cone-Wesson, 2005; Terband et al., 2018).
  • May have hearing loss (Cone-Wesson, 2005).
  • Receptive and expressive language problems (Wyper & Rasmussen, 2011).
  • Difficulties with narrative discourse, particularly errors in nominal reference (Thorne et al., 2007).
  • Difficulties with social communication (Coggins et al., 2007).

Fragile X Syndrome

Fragile X syndrome is the most common inherited cause of ID (Lozano et al., 2014). Deficits are more severe for boys than for girls (Haebig et al., 2020). Characteristics may include the following:

  • Delayed speech and language skills, particularly syntax, with relative strengths in vocabulary and language comprehension (J. E. Roberts et al., 2008).
  • Difficulties with articulation, fluency, and oral motor skills (J. E. Roberts et al., 2003).
  • Prolonged unintelligible speech, particularly in connected speech (Barnes et al., 2009). 
  • Social interaction and pragmatic difficulties similar to those associated with ASD (e.g., staying on topic, taking turns in conversation, echolalia, perseveration; Haebig et al., 2020).

Other conditions that may also co-occur with ID include the following:

  • anxiety disorder
  • attention-deficit/hyperactivity disorder
  • dysphagia (Chadwick & Joliffe, 2009)
  • depressive and bipolar disorder
  • impulse-control disorder
  • major depressive disorder (APA, 2013)

Associated Health Conditions

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

Associated health conditions with higher prevalence in individuals with ID include the following:

  • anxiety disorders (Oeseburg et al., 2011)
  • hearing loss (Herer, 2012)
  • physical coordination and tone issues (Vuijk et al., 2010)
  • heart conditions (Patja et al., 2001)
  • obesity-related problems (Rimmer et al., 2010)
  • seizure activity (Oeseburg et al., 2011)
  • visual impairment (Warburg, 2001)

Addressing health inequalities as well as providing adequate health care and medical training may improve quality of life and increase longevity in individuals with ID.

Content Disclaimer: The Practice Portal, ASHA policy documents, and guidelines contain information for use in all settings; however, members must consider all applicable local, state and federal requirements when applying the information in their specific work setting.

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