What qualifies as an intellectual disability?

Bedside Tests of Memory and Cognitive Function

The most important point to be made about bedside evaluations of cognition and memory is that they are an integral part of the neurological examination and a tool by which the neurologist localizes lesions affecting the higher cortical functions, just as the motor or cerebellar examinations localize neurological deficits. The most common error made by neurologists is to omit a systematic evaluation of mental function in patients who seem “alert and oriented.” Deficits of memory, deficits in fund of knowledge, or focal deficits such as alexia, apraxia, agnosia, acalculia, or constructional impairment can be missed. Some patients have a “cocktail party” conversational pattern that belies such deficits; others become expert at deferring questions to a spouse or family member. Every neurologist has the task of deciding which patients need formal cognitive testing and whether to make up an individual test routine or to rely on one of the standard tests. Again, it is more important to make the assessment than to follow a specific format.

The formal mental status examination should always include explicit testing of orientation including the date, place, and situation. Memory testing should include an immediate attention test, of which the most popular are forward digit span, serial-7 subtractions from 100, or “spell world backward.” Short-term memory should include recall of three to five unrelated words at 5 minutes followed by a recognition paradigm to elicit recall of unremembered words. Importantly, the patient must say all the words after presentation to make sure the items have been properly registered. At times, nonverbal short-term memory, such as recalling the locations of three hidden coins or reproducing drawings, can be useful to test, especially in the case of profound aphasia or verbal impairments. Remote memory can be tested by having the patient name children or siblings. Fund of information can be tested with recall of recent presidents or other political figures. For patients who do not pay attention to politics, use of athletic stars or television celebrities may be more appropriate. Language testing should include spontaneous speech, naming, repetition, auditory comprehension, reading, and writing (the bedside language test is described in more detail inChapter13) . In our practice, we show patients more difficult naming items such as the drawings from the National Institutes of Health (NIH) Stroke Scale or body parts such as the thumb or the palm of the hand. Praxis testing should include the use of both imaginary and real (e.g., saw, hammer, pencil) objects. Both hands should be tested separately. Calculation tasks include the serial-7 subtraction test and simple change-making problems. Visual-spatial-constructional tasks can include line bisection, copying a cube or intersecting pentagons or another design, or drawing a clock or a house (Fig. 7.3). Many neurologists supplement assessment of this domain with the clock-drawing test. Insight and judgment are generally best tested by assessing the patient’s understanding of his own illness. Formal assessment includes interpretation of proverbs (e.g., “Those who live in glass houses should not throw stones”) or abstraction (stating how an apple and an orange are similar). Another bedside tool used to test frontal lobe processing, or executive function, is the copying and continuation of Luria’s test of alternating sequences (sequential squares and triangles; seeFig. 7.1). A similar measure, also attributed to Luria, is the “fist/side/palm” repetitive movement. With these tests, preliminary localization can be made in the deep memory structures of the medial temporal lobes, the left hemisphere language cortex in the frontal and temporal lobes, the left parietal region (calculations, apraxia), and the right parietal lobe (visual-constructional tasks), or the frontal lobes (insight and judgment, proverbs, similarities, Luria’s sequence test).

Introduction

Intellectual disability (ID), formerly known as mental retardation, is a disability of intellectual functioning and adaptive behavior that arises during the period of time from conception to the beginning of adulthood. With ID, the individual has significant limitations in both intellectual ability and adaptive behavior, which are manifest before the age of 18.

Individuals with ID are of every culture, language group, and socioeconomic level. Most people with ID do not look any different from people who do not have ID, nor do they differ in their dreams, goals, or feelings. What is different is that they have significantly limited intellectual functioning, usually an IQ that is at least two standard deviations (SD) below the mean, and significantly reduced adaptive behavior that is also at least two SDs below the mean. Two SDs approximates 2nd to 3rd percentile, such that ID is characterized by intellectual and adaptive functioning that are less well developed than approximately 97% of the population. In addition, individuals have had these limitations since a young age (below age 18) and have grown up with the disability.

Many different labels or names have been used over time to describe people with ID, including mental retardation, mental deficiency, feebleminded, idiot, imbecile, moron, etc. The names are often hurtful and demeaning, and can serve to inadvertently psychologically and physically separate individuals with ID from their age peers and communities. Periodically, with push from self-advocates and their friends and families, the name has changed to something more acceptable. Currently, the preferred label or name is ID. In 2012, the federal government mandated this name change in all federal legislation (Rosa’s Law, 2010). In addition to proper terminology, it is important to use ‘person first’ language, which refers to an individual as a person with intellectual disability and never as an intellectually disabled person. This distinction affirms that individuals with ID are complex human beings first, like everyone else, and not solely their disability.

Some people with ID have several disabilities, for example, they may also have a mental health problem and/or Down syndrome, autism spectrum disorder, or another disability. Many people with ID may also be referred to as having a developmental disability. As IQ decreases, the likelihood of health impairments and other disabilities increases. Mental disorders and psychiatric symptoms occur in some persons with ID and cause stress for the individuals as well as their families, friends, and support providers, just as is seen in individuals who do not have ID. Overall prevalence rates for psychiatric symptoms or disorders in people with ID have been reported to range from approximately 13% to 75% depending on the definition and diagnostic criteria used, assessment tools, and whether the samples were administratively based or population-based. When using population-based samples, it appears that approximately 25% of people with ID have mental health problems (Buckles et al., 2013), which is similar to the general population (National Institute of Mental Health, n.d.).

Often, the etiology of ID in an individual cannot be determined. Generally, the causes of ID can be grouped in four broad categories: biomedical factors, such as chromosomal disorders; social factors, such as poverty; behavioral factors, such as parental alcohol use; or educational factors, such as inadequate early intervention. These causes may occur at the prenatal, perinatal, or postnatal stages of development.

In this article, I will review the current state of knowledge about ID pertaining to issues of definition, assessment and diagnosis, functioning, classification systems, disability rights, important life issues, and current challenges.

Diagnostic Criteria

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairments in two areas: (1) deficits in social communication and social interactions; and (2) restricted and repetitive patterns of behavior, interests, and activities (APA, 2013a). With the revisedDiagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), ASD now subsumes what were previously separate diagnostic categories of autistic disorder (also referred to as classic autism or early infantile autism), pervasive developmental disorder–not otherwise specified (PDD-NOS), and Asperger syndrome. The changes are based on research results which, thus far, have failed to document either PDD-NOS or Asperger syndrome as separate biological entities. The prior diagnostic manual also included deficits in language expression as a criterion, but this is no longer the case as not all children with ASD have language disorders. However, pragmatic language skills are incorporated into the social domain as all individuals with ASD have deficits in this domain of language. Under the DSM-5, diagnosis of ASD requires an individual to exhibit three deficits in social communication and at least two symptoms in the category of restricted range of activities/repetitive behaviors. Within the second category, a new symptom is included: hyper- or hyporeactivity to sensory input or unusual interests in sensory aspects of the environment. Deficits in social communication and interactions include those in social reciprocity, nonverbal communication, and skills in developing, maintaining, and understanding social relationships. Symptoms must be present in early development but need not be shown until social demands exceed the individual’s capacity. Furthermore, DSM-5 specifies three levels of severity (mild, moderate, severe) rated separately for social communication and restricted, repetitive behaviors, based on what level of support the individual requires. In addition to the diagnosis, individuals are also described in terms of any known genetic cause (e.g., fragile X syndrome [FXS], Rett syndrome), level of language and intellectual disability (ID), and presence of medical conditions such as seizures, psychiatric disorders (e.g., anxiety, depression), and/or gastrointestinal disorders. (SeeBox 90.1 andTable 90.1 for DSM-5 criteria for ASD.) The range of disabilities seen among children on the spectrum cannot be overemphasized.

Abstract

Individuals with intellectual disabilities have unique and varied behavioral issues and consequent needs. The definition of an intellectual disability is three-pronged: having subaverage intelligence and impaired adaptive behavior, both of which manifest before the age of 18. Different types of intellectual disabilities exist; certain genetic conditions, such as Williams syndrome, Prader–Willi syndrome, and Down syndrome, are associated with certain behavioral characteristics and outcomes. In addition to having an intellectual disability, many of these individuals have additional diagnoses of mental health disorders. Due to deficits related to their intellectual disabilities, these individuals may need academic, social/adaptive, and mental health interventions.

Diagnosis

The diagnosis is based on clinical symptoms consistent with theDiagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5). Symptoms must be present in the early developmental period and cause clinically significant impairment in social, occupational, or other important areas of functioning. ASD may occur with or without accompanying intellectual impairment and language impairment. ASD may be associated with a known genetic or medical condition, with another neurodevelopmental or behavior disorder, and with catatonia. Full evaluation should include a detailed history of presenting symptoms and early development, and observation of the child in a setting where social interaction is required. Although there is no psychological “test” for ASD, validated, structured observation tools may be employed as a component of a detailed diagnostic evaluation. Of these, the most commonly seen is the Autism Development Observation Scale (ADOS), available in multiple versions appropriate for different age groups, and including a version for diagnosis in adults. It is important for practitioners to be aware of local regulations. In some states, access to resources (e.g. early childhood intervention, respite care, applied behavioral analysis, etc.) may only be triggered after specific evaluation requirements are met; those may include assessment by certain kinds of professionals, evaluation in approved settings, or the use of specific tools.

There is a difference between a clinical diagnosis of ASD and a determination that a child is eligible for autism-related educational services. Children with a clinical diagnosis may not necessarily be eligible for special educational services. The latter are determined by assessment for educational need and may be delivered through an Individualized Education Plan (IEP). Families may benefit from advocacy in accessing educational services for social and behavioral difficulties, even when their child is doing well academically. On the other hand, not every child deemed eligible for educational services for autism will have received a formal clinical diagnosis. The latter is important when a child transfers to adult services, when a clinical diagnosis may be necessary to determine eligibility for disability, guardianship, vocational education, or sheltered workshops and group homes.

Abstract

Intellectual disability (ID) or intellectual developmental disability (IDD) is one of the commonest neurodevelopmental disabilities worldwide and is known to affect 2% of the population of France or just over a million people. It is marked by a reduced ability to reason and understand abstract or complex information, which heavily restricts school learning and limits the individual's ability to adapt to daily life, including their transition to adulthood. Intellectual handicap or mental handicap results from an interaction between the individual vulnerability of a person with ID and their ecosystem, in other words, their family, and cultural and institutional environment, which can be a barrier or a facilitator. Identifying a child with an unusual developmental trajectory requires professionals to have a good understanding of psychomotor development. ID may be isolated but is very often intertwined with other neurodevelopmental disorders, including autism, motor or sensory difficulties (hearing, vision), serious sleep and eating disorders, and medical conditions such as epilepsy, as well as a wide variety of psychopathologic problems, including anxiety, depression, and emotional regulation disorders. There are many causes of ID. More than half of all cases are genetic in origin, and there are several hundreds of rare diseases about which little is known so far. The use of new genetic techniques (high-throughput sequencing) should reduce the number of people who are undiagnosed and give way to a comprehensive diagnostic approach based on clinical practice. A regular multidimensional evaluation of cognitive, educational, socioemotional, and adaptive skills throughout life provides a better understanding of how individuals with ID function and will contribute toward the planning of more appropriate strategies for learning, care, and support, leading to a better quality of life and participation in society.

Dual Diagnosis

While the term ‘intellectual disability’ has referred to individuals with cognitive impairments and difficulties with day-to-day adaptation, individuals with intellectual disability are often at risk for showing other behavior problems beyond those captured in this definition. As a result, many individuals have been dually diagnosed with both intellectual disability and other co-morbid conditions, such as psychiatric disorders. The reported prevalence of individuals with dual diagnoses varies from study to study, with some reports as high as 40–50% of children with intellectual disability in middle childhood showing some degree of psychiatric symptomatology.

In addition, children with specific causes of their intellectual disabilities may be vulnerable to some psychiatric conditions, but not others. For example, individuals with Prader–Willi syndrome show increased rates of obsessive-compulsive behavior, including hoarding behavior, as well as well-documented obsessive food ideation symptoms. Children with Williams syndrome are at increased risk of showing difficulties in the area of anxiety and heightened fear responses. While children with Down syndrome tend to show lower levels of psychopathology than other children with intellectual disability, there is evidence to suggest that these individuals are at increased risk for autism and autism spectrum disorders, relative to the prevalence rates observed in the typically developing population.

Diagnosis of a comorbid psychiatric condition along with intellectual disability may pose many challenges to clinicians and therapists. Researchers in this area have noted that many clinicians are prone to attribute the behavior problems associated with psychiatric conditions to the diagnosis that a child already has, leading to the phenomenon called diagnostic overshadowing. In other words, the diagnosis that a child already has – for example, Down syndrome – becomes the explanation for poor communication and impairments in social interaction, rather than exploring the alternative possibility that the child might meet criteria for autism as well. This is notable in that impairments in social interaction are unusual in most children with Down syndrome, who tend to show competence in achieving early intersubjective milestones in infancy and toddlerhood. Thus, understanding the relative contributions of the intellectual disability and a possible comorbid disorder may make it possible to improve the precision with which decisions are made regarding appropriate services and intervention strategies.

Yet, making dual diagnoses of this nature can be challenging for a number of reasons. First, the manifestation of a psychiatric disorder may be modified in an individual with intellectual disability. For example, an anxiety disorder may manifest itself differently in a child who has pronounced expressive language delays versus a child who has an age-appropriate ability to express his/herself. In addition, when a child has pronounced intellectual disability that are in the severe or profound IQ score range, additional difficulties present themselves with regard to accurate dual diagnosis. If a low-functioning child with Down syndrome shows many of the behavioral hallmarks of autism, including poor joint attentions skills, poor initiation, language delays, or a lack of pretend play, it is possible that the child simply has not yet reached an overall developmental level wherein a clinician would expect to observe those behaviors. As a result, an autism diagnosis may not be appropriate in this situation, especially if these deficits are observed in the context of some other, more basic behaviors that evidence impairment in social interaction (e.g., sharing enjoyment or interest).

Psychology of Exceptionality

Children and adults with intellectual disability share an attribute with all other minority groups: they are different. The difference may be real or perceived, but the effect is substantial. Difference begins with the altered expectations of parents when they learn about the prospect of cognitive disabilities. A newborn with Down syndrome may lack none of the capabilities of other newborns, but that infant is perceived as different. Deeply entrenched cultural attitudes may serve to assign a negative connotation to this difference and reinforce the parents' sense of alarm. Counselors assisting parents during the period of diagnostic crisis, whether this be in early infancy or in later years, must reckon with the personal significance of difference.

When one examines the characteristics of difference for an individual with intellectual disability, one notes several components, all of which are to some extent dynamic. First is the matter of achievement and performance, in the measured or standard sense. This matter is linked to the functional limitation present, of cortical origin. As mentioned previously, however, the final effects of constraints in intelligence are modulated by concurrent attainments in adaptation. If expectations remain low, elements of self-fulfilling prophecy intrude on performance.

The second dissimilarity is that of requirements for services provided to the individual and family to allow maximal realization of potential. This is real and not always easy, but fits justifiably within the spectrum of contributions expected among people and their agencies. All of us draw on inside and outside services in this social world; for individuals with significant exceptionality, the urgency is greater.

A third difference can be that of participation in life events and sequences, or involvement in the usual experiences of growth and daily living. For a child with intellectual disability, this has a considerable cultural prescription. Descriptors such as normalization, communitization, least restrictive environment, and inclusive society speak to the current resolve to provide an enhanced setting for participation in usual form. In the external sense, the victories of the past several decades in the human rights area provide assurance that joining in school, community, and residential settings will be guaranteed. The right to establish contracts (e.g., marriage and ownership), with guidance as appropriate, also assists in the reversal of historical limitations.

The fourth or final difference could be that of connectedness. Here there can be no fundamental or primary defense, although societal weakness or clouded vision has often deprived us all of full fellowship.

It is conceded that difference is present in the best of times. Thinking about the difference in the context of its components (mentioned previously) may diminish the first impressions of oppressiveness and give some guidance about best plans for helpful actions. When one shares time and experiences with families who have children with intellectual disability, one is taught some precious lessons about the ultimate meaning of the residual differences. It becomes clear that the importance of less-than-superior skills is a matter of personal interpretation and is not absolute. If the job is well done within the context of native talents, and if the pursuit of referenced happiness and best quality of life is honored, the measured features of performance seem less prominent. Diversity among humans is a richness. When appropriate support systems are in place, and a cordial environment exists, parents come to assign uncommon value to their exceptional family member. The differences are often accommodated with grace. Professionals frequently damp the natural strengths of families to love and succeed.

DEFINITIONS AND ETIOLOGY

Intellectual disability (ID) is the current term used to describe what in the United Kingdom has been known as learning disability and in the United States as mental retardation. In Australia, the 1986 Victorian Act of Parliament, which established the basis on which services to people with intellectual disabilities or significant delay in their development are provided, defines intellectual disability as follows:

Intellectual disability in relation to a person over the age of five years means a significant subaverage general intellectual functioning existing concurrently with deficits in adaptive behaviour and manifested during the developmental period. (Intellectually Disabled Persons Services Act, 1986)

The threshold at which general intellectual functioning is considered “subaverage” is often fixed at an IQ of 70, two standard deviations below the mean IQ. Controversially, in 1992 the American Association on Intellectual and Developmental Disabilities (AAIDD) loosened this threshold to include people with IQs in the range of 70 to 75. The AAIDD also required 2 out of 10 areas of adaptive functioning to be assessed to have deficits. This definition was adapted by the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV). In 2002, the AAIDD reinstated the IQ 70 threshold and required deficits in conceptual, social, and practical adaptive skills to be present. These changes in definition have implications for epidemiologic data collection, but the key concept of ID remains. An IQ of less than 70 is necessary, but this in itself is inadequate for the diagnosis to be made. There has to be evidence of both a developmental disorder, that is onset during childhood, and deficits in adaptive behavior for the diagnosis to be made.

Further classification of ID can be made within the broad definition. The Diagnostic Criteria for Psychiatric Disorders for Use with Adults with Learning [Intellectual] Disabilities (DC-LD)1 describes a person with ID’s mental health in terms of ID severity, ID etiology, and related mental disorders (developmental disorders, psychiatric illness, personality disorders, problem behaviors, and other disorders). Severity is grouped according to IQ as 50-69 mild ID, 35-49 moderate, 20-34 severe, and less than 20 profound. The Swedish model of ID classification developed by Kylen2 is often helpful in clinical situations where IQ is not known:

Severe: Communication is based on simple nonverbal signs, no verbal communication, no concept of time or space. Equivalent to IQ <10.

Moderate: Limited verbal skills. Limited understanding of local space. Can structure thoughts in relation to individual experiences. Equivalent to IQ 10 to 40.

Mild: Basic literacy and mathematical skills present. Can rearrange, structure, and perform concrete cognitive operations. Equivalent to IQ 41 to 70.

In addition, the DC-LD includes appendices that relate to medical factors influencing health status and contact with health services. The latter are highly relevant because developmental disorders that affect the brain, giving rise to ID, often affect other body systems also.

The etiology of ID is frequently unknown in older adults, but it can be considered along conventional lines of external causes (infection, injury, poisoning), internal disorders (endocrine, metabolic), perinatal insults, and congenital conditions (chromosomal abnormalities, gene mutations). The latter are of particular relevance to the health of older adults with ID, as specific syndromes are associated with risk of particular physical disorders and diseases. Common syndromes seen in older adults include Down syndrome (DS), Angelman syndrome, fragile X syndrome, Klinefelter syndrome, Turner syndrome, and Williams syndrome. Table 58-1 provides a brief description of these syndromes. It is worth noting that, given the preceding definition of ID, by no means does everyone with one of these syndromes fulfill the diagnostic criteria for ID; this is particularly true of women with Turner syndrome who have a tendency for nonverbal cognitive deficits but are often of average intelligence.

Just as there is a considerable overlap between congenital syndromes, such as DS and ID, there is a similar overlap between ID and autism. The diagnosis of autism depends on (1) abnormal social development, (2) communication deficits, and (3) restricted and repetitive interests and behavior. Around three quarters of people with autism have a nonverbal IQ less than 70 and hence also fulfill diagnostic criteria for ID; but in autism, social and communication skills are worse than expected for any given nonverbal IQ.

Intellectual disability (ID) is a broad disorder characterized by early onset limitations in intellectual functioning and adaptive behavior. Genetic and functional studies have revealed a role for epigenetics in the underlying pathology of ID. ID can result from aberrant epigenetic silencing of important neuronal genes or from mutations in core members of the epigenetic machinery. Aberrant epigenetic silencing occurs in the nucleotide repeat disorder, fragile X syndrome, and in the imprinting disorders Angelman syndrome and Prader–Willi syndrome. Mutations in epigenetic regulators are found in a diverse array of ID disorders, including Rett syndrome, ATR-X syndrome, Rubenstein–Taybi syndrome, and Kleefstra syndrome. There are over 30 ID genes encoding proteins that have a direct role in modification of chromatin structure, and these proteins participate in DNA methylation, ATP-dependent chromatin remodeling, and posttranslational modification of histones. Recent studies are beginning to reveal a complex role for epigenetic regulators in human cognition.