Intellectual Disability (Comprehensive Concise)

Historical Overview

  • Evolution of terminology for intellectual disability (ID) and emphasis on "people first" language.

  • Shift in understanding and treatment of ID between extremes of exaltation and vilification.

  • Early recognition and treatment of ID in ancient medical writings (Hippocrates, Galen) and Middle Ages (Avicenna).

  • Esquirol (1838) distinguished ID from mental illness, focusing on congenital onset.

  • Jean-Marc Itard's experiment with Victor, a "wild-child," marked the idea that persons with disabilities might be educable.

  • Move toward "deinstitutionalization" due to overcrowding, neglect, and philosophy of "normalization".

  • Parent and professional advocacy groups fought for legislative and legal victories to decrease the size of large institutions.

Schooling

  • Classes for "problem children" began in the late 1800s, with the first classes specifically for children with ID in 1894.

  • Lloyd Dunn (1968) questioned the need for segregated special education classes, advocating for mainstreaming.

  • Post-1970 era witnessed the strong influence of mainstreaming, community living, and normalization.

Research

  • Esquirol (1838) differentiated ID from mental illness and proposed several levels of impairment.

  • J. Langdon Down (1866) proposed a system of "ethnic classifications".

  • Early genetic research focused on the inheritance of ID and eugenic sterilization.

  • Henry Goddard used Binet and Simon’s IQ tests in the United States.

  • Progress in behavioral and biomedical fields, including tests of motor, nonverbal intelligence, adaptive behavior, and studies of psychiatric disorders in individuals with ID.

  • Folling (1934) hypothesized that patients with ID were unable to metabolize phenylalanine, leading to dietary treatment of PKU.

  • Lejeune, Gautier, and Turpin (1959) discovered that most cases of DS were due to trisomy of the 21st chromosome.

  • Discovery of FXS (1969) and refinement of its cytogenetic diagnosis in the mid-1970s.

Organizations

  • Association of Medical Officers of American Institutions for Idiotic and Feeble-Minded Persons began in 1876, forerunner to AAIDD.

  • Council for Exceptional Children (CEC) began in 1922, championing special education.

  • The Arc (formerly NARC) is the main parent-led advocacy group and was influential in the passage of the Education for All Handicapped Children Act of 1975.

  • NADD was established in 1983, specifically in recognition of the lack of attention by the professional community to the needs of individuals with ID who also experience psychiatric illness.

  • Federal agencies such as NICHD and UCEDDs have supported disability research and policy.

Definition of Intellectual Disability

*APA DSM-5 definition of ID aligned with AAIDD, replacing "mental retardation."
*Severity levels are classified by adaptive rather than intellectual function or IQ scores.
*Standardized intelligence tests are used to identify ID, but administering tests to people with ID is challenging.
*Adaptive Functioning: Adaptive behavior is measured by performance as opposed to ability.

Severity of Intellectual Disability

*DSM-5 provides a classification system based on adaptive functioning across three domains: conceptual, social, and practical.
*Mild ID: Many achieve academic skills at the sixth-grade level or higher, function in the mild range of ID.
*Moderate ID: Most children with moderate ID require special education services, achieving academic skills at the second to third grade level.
*Severe ID: Individuals at this level often have one or more organic causes for their delay and require close supervision and specialized care throughout their lives.
*Profound ID: Involves pervasive deficits in cognitive, motor, and communicative functioning and most require total supervision and care throughout life.

Prevalence

  • DSM-5: 1% of the population has an ID.

  • Rates are higher in males and peak around ages 10 to 14.

  • Individuals of lower socioeconomic status and of ethnic minority groups show higher-than-expected rates of ID.

Etiology of Intellectual Disability

  • ID results from brain dysfunction due to abnormal brain development or brain injury from genetic and environmental causes.

  • Genetic causes can result in multiple malformation conditions or “non-syndromic” ID.

  • Various inheritance patterns and genetic mechanisms are involved.

  • Specific genetic diagnoses influence treatments and health implications for family members.

Medical Diagnostic Approach

  • Comprehensive clinical evaluation includes history, family pedigree, and physical examination.

  • Genetic evaluation for chromosomal abnormalities and fragile X.

  • Neuroimaging is indicated for specific conditions.

  • Electroencephalography may be useful in patients with seizures or specific genetic syndromes.

  • Metabolic testing for inborn errors of metabolism (IEMs).

Genetic Intellectual Disability Syndromes and Behavioral Phenotypes

  • Behavioral phenotype: syndrome in which the probability of certain behaviors is greater than expected.

  • Examples: FXS, PWS, DS, and Williams syndrome.

Fragile X Syndrome (FXS)

  • Caused by amplification of CGG trinucleotide sequences in the FMR1 gene.

  • Males are more often and more severely affected than females.

  • Behavioral features are a function of the number of CGG repeats and the amount of FMRP produced.

  • Commonly co-occurs with Autism Spectrum Disorder (ASD)

Prader-Willi Syndrome (PWS)

  • Caused by the loss of the paternal copy of the PWS critical region on chromosome 15q11.2–13.

  • Characterized by hypotonia, feeding-sucking difficulties, hyperphagia, and food-seeking behavior.

  • High proportion of persons also show nonfood obsessions and compulsive behaviors and are at increased risk for obsessive-compulsive.

Down Syndrome (DS)

  • Most often the result of nondisjunction of chromosome 21.

  • Distinctive cognitive and linguistic profiles, with strengths in visual versus auditory processing.

  • Adaptive skills are not uniform, with communication scores trailing behind measures of daily living skills and socialization.

  • Psychopathology is less serious compared to others with ID.

Williams Syndrome

  • Caused by a microdeletion on chromosome 7 that includes the gene for elastin.

  • Show hyperacusis, hypercalcemia, neuromusculoskeletal and renal abnormalities, and characteristic facial features.

  • Relative strengths in verbal short-term memory and language.

  • Social disinhibition, ADHD and anxiety are commonly co-occurring

Smith–Magenis Syndrome (SMS)

  • Genetic syndrome with characteristic sleep/circadian rhythm disruption, self-injury and behavioral issues. Melatonin helpful.

Developmental Considerations in Children with ID

Children with ID traverse the same sequences in their development as do children with typical development, but in the setting of certain forms of ID there are strengths and weaknesses not generally found in typically developing children.

  • Sequences: Similar sequences have been found for a variety of children over many tasks.

  • Cross-Domain Relations: Groups of typically developing children show from one domain to another.

  • Developmental Rates: Children with ID develop at slower rates than typically developing children.

  • Mother–Child Interactions:Mothers of children with ID are worried about their child’s development: in their zeal to teach and instruct their children, these mothers might inadvertently be using a style of interaction that is not the most effective.

  • Family Reactions: Families of children with ID as families facing increased stress. And while children with ID might add stress to the family system.

Psychopathology in Intellectual Disability

  • Individuals with IQs below 70 have a two- to fivefold higher rate of psychiatric disorders compared with typically developing persons.

  • Specific risk factors include moderate versus mild levels of intellectual impairment, adaptive behavior deficits, poor socialization, language impairments, living with one biologic parent, and low family SES.

  • The DM-ID provides adapted diagnostic criteria for psychiatric diagnoses in this population.

Treatment of psychiatric problems

Multimodal: Combination of:

  • Psychoeducational.

  • Psychotherapeutic.

  • Psychopharmacological interventions.

Psychotherapy

*Active therapeutic stance be employed, as well as concrete and supportive interventions and careful attention to the language abilities and developmental level of the patient in treatment.

Pharmacotherapy

  • There is a relative paucity of controlled clinical drug trials that include persons with ID, particularly individuals with the most severe cognitive impairment. As a result, clinicians must generally extrapolate from the general population with regard to pharmacotherapy in persons with ID.

Services and Supports

*From ages 3 to 21, specialized education services are provided through local school districts.
*Adult Services: Federally mandated school services serve students with disabilities from age 3 to age 21. There is a federal mandate requiring youth with disabilities age 16 and older to have a postsecondary transition plan written into their IEP.

Legal Issues in Intellectual Disability

*Individuals with more severe or profound ID may be “protected” by factors including supervision from caregivers and a reduced range of social activities and community interface.
*The ADA of 1990 spells out four aims: (1) to provide a clear and comprehensive national mandate for the elimination of discrimination against individuals with disabilities;