What percentage of cases of intellectual disabilities Cannot determine a cause?

Clinical Manifestations

Early diagnosis of ID facilitates earlier intervention, identification of abilities, realistic goal setting, easing of parental anxiety, and greater acceptance of the child in the community. Most children with ID first come to the pediatrician's attention in infancy because of dysmorphisms, associated developmental disabilities, or failure to meet age-appropriate developmental milestones (Tables 53.2 and53.3). There are no specific physical characteristics of ID, but dysmorphisms may be the earliest signs that bring children to the attention of the pediatrician. They might fall within a genetic syndrome such as Down syndrome or might be isolated, as in microcephaly or failure to thrive. Associated developmental disabilities include seizure disorders, cerebral palsy, and ASD.

Most children with ID do not keep up with their peers' developmental skills. In early infancy, failure to meet age-appropriate expectations can include a lack of visual or auditory responsiveness, unusual muscle tone (hypo- or hypertonia) or posture, and feeding difficulties. Between 6 and 18 mo of age, gross motor delay (lack of sitting, crawling, walking) is the most common complaint. Language delay and behavior problems are common concerns after 18 mo (Table 53.4). For some children with mild ID, the diagnosis remains uncertain during the early school years. It is only after the demands of the school setting increase over the years, changing from “learning to read” to “reading to learn,” that the child's limitations are clarified. Adolescents with mild ID are typically up to date on current trends and are conversant as to “who,” “what,” and “where.” It is not until the “why” and “how” questions are asked that their limitations become apparent. If allowed to interact at a superficial level, their mild ID might not be appreciated, even by professionals, who may be their special education teachers or healthcare providers. Because of the stigma associated with ID, adolescents may use euphemisms to avoid being thought of as “stupid” or “retarded” and may refer to themselves as learning disabled, dyslexic, language disordered, or slow learners. Some people with ID emulate their social milieu to be accepted. They may be social chameleons and assume the morals of the group to whom they are attached. Some would rather be thought “bad” than “incompetent.”

Children with ID have a nonprogressive disorder; loss of developmental milestones or progressive symptoms suggest another disorder (seeChapter 53.1).

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.

B Intellectual Disability

1.

Definition and Epidemiology

Deficits in general mental abilities

Affects approximately 1% of the population4

Clinical Presentation

Delay in milestones (motor, language, social)

Academic difficulty

Identifiable features of known associated genetic syndrome (e.g., Trisomy 21, fragile X, Rett syndrome)

Diagnosis

Diagnostic criteria: (1) deficits in intellectual functioning, (2) deficits in adaptive functioning, (3) onset of these deficits during the developmental period

Deficits in adaptive functioning must be in one or more domains of activities of daily living.

ID is further categorized as mild, moderate, severe, or profound in the DSM-5 based on the degree of functional deficit (Table EC 9.B).

Interventions/Treatment

Table EC 9.B. Severity Levels for Intellectual Disability

Reprinted with permission from the American Psychiatric Association.Diagnostic and Statistical Manual of Mental Disorders. 5th ed. Arlington: APA; 2013.

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.

Intellectual Disability: Intellectual Developmental Disorder

In 2007, the American Association on Mental Retardation changed its name to the American Association on Intellectual and Developmental Disabilities and urged the use of the termintellectual disability rather thanmental retardation to refer to a disability characterized by significant limitations both in intellectual functioning (reasoning, learning, problem solving) and in adaptive behavior that arises before 18 years old. In October 2010, President Obama signed S. 2781, also calledRosa's law. This law requires that the termsmental retardation andmentally retarded individual be changed, in all federal law, tointellectual disability andindividual with an intellectual disability, respectively. This bill was originally introduced by Senator Barbara Mikulski of Maryland. She named the bill “Rosa's law” after a young woman in her state who successfully advocated for the elimination of the phrase “mentally retarded” in all state law.

Limitations in intellectual functioning is generally defined as scores on standardized intelligence quotient (IQ) tests that are two or more standard deviations below age-group norms;adaptive behaviors refers to the broad areas of conceptual, social, and practical functioning, such as learning, communication, self-care, community participation (e.g., riding public transportation, engaging in recreation, voting), and social interactions.

Intellectual disability cannot be diagnosed until the child is old enough to take a standardized IQ test (generally at least 3 to 4 years old). Before that time, a child with delays in two or more domains of development may be described as having global developmental delay; some of these children will later be diagnosed with an intellectual disability. The ability to predict intellectual performance and academic achievement from developmental testing during infancy is quite limited. Only in children falling extremely far behind age expectations should one anticipate permanent intellectual disability. If an infant shows delayed cognitive development, the parents' reasonable concerns can be met with a referral to an early intervention program to increase the probability of improvements over time.

As children with early developmental delays approach school age, particularly if they have had optimal educational support, the ability to predict later difficulties improves. The rate of developmental progress during the preschool years is often a good predictor of later intellectual performance. After initial cognitive developmental delays, if a child can achieve 6 months' progress in 6 months, the prognosis for normal intellectual capacity is good. However, if the child achieves, for example, 4 months' progress in 6 months, the rate of development is 67% of the expected rate and the prognosis for later normal intellectual functioning is poor. By the time a child is 6 to 7 years old, limitations as measured on an IQ test typically characterize the individual's abilities throughout life. At that point, the termintellectual disability replacesglobal developmental delay because the probability that the delay will resolve is very low.

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.

Intellectual disability/intellectual development disorder (ID/IDD)

ID is diagnosed when a patient has deficits in the intellectual functions (e.g., reasoning, problem-solving, planning, and learning) and in adaptive behavior (e.g., communication, social skills, and personal independence). These phenotypes have to emerge during the developmental period for a formal diagnosis.1, 7 The latest guidelines for diagnosis in DSM-V classify the severity based on milestones in personal skills, but more often the severity is determined by the IQ of the patient as described in the previous edition of DSM: profound ID (IQ < 20), severe ID (IQ 20–34), moderate ID (IQ 35–49), and mild ID (IQ 50–69). A further distinction is made between syndromic and nonsyndromic ID, based on the exclusive presence of ID in the patient (nonsyndromic) or when the ID is presented together with additional features such as (facial) dysmorphisms or congenital anomalies (syndromic).8 For children under the age of 5 that fail to meet the expected developmental milestones and cannot be reliably and systematically assessed for intellectual functioning, the diagnosis (global) developmental delay can be made. Theoretically the prevalence of ID in the population is 2%–3%, but the actual number depends on gender, maternal race, and socioeconomic and educational status.9 In approximately 65% of the moderate to severe ID patients, a genetic aberration that causes the disease can be identified.8

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.