Intellectual disability

• ANATOMY OR SYSTEM AFFECTED: Brain, nervous system, psychic-emotional system

DEFINITION: Significant subaverage intellectual development and deficient adaptive behavior often accompanied by physical abnormalities.

Causes and Symptoms

Intellectual disability is a condition in which a person demonstrates significant limitations in both intellectual functioning and adaptive behavior. Diagnosis can be made at birth if intellectual disability is accompanied by physical abnormalities. However, an infant with mild intellectual disability may not be diagnosed until problems arise in school. The prevalence of intellectual disability is estimated to be between 1 and 3 percent of the world’s total population.

Diagnosis of intellectual disability is made on the basis of three criteria: "significant subaverage" intellectual functioning, "significant subaverage" adaptive behavior, and onset before the end of the developmental period, typically defined as age eighteen. The American Psychiatric Association (APA) defines "significant subaverage" performance in either intellectual functioning or adaptive behavior as being "at least two standard deviations below the average level for the individual’s peers," according to Marc J. Tassé.

Intellectual functioning is measured by intelligence quotient (IQ) testing. Adaptive behavior is not as easily measured as an IQ, but it is generally defined as the ability to meet social expectations in the individual’s own environment. Assessment is based on development of certain skills, such as sensorimotor, speech and language, self-help, and socialization skills. Tests have been developed to aid in these measurements.

Prior to the release of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5, 2013), the APA categorized severity levels of intellectual disability according to IQ scores. In the DSM-5, however, the APA abandoned this classification, choosing instead to use "the individual’s adaptive functioning level across conceptual, social and practical skills to guide clinical judgment in determining the severity level of intellectual disability," again according to Tassé. The four severity levels are mild, moderate, severe, and profound. In DSM-5-TR, the 2022 Text Revision of DSM-5, the APA updated the name of the disorder to "intellectual developmental disorder (intellectual disability)" to better connect with the World Health Organization's International Classification of Diseases, eleventh revision (ICD-11). DSM-5-TR also had changes to the diagnostic features section.

To identify possible intellectual disability in infants, the use of language milestones is a helpful tool. For example, parents and pediatricians will observe whether children begin to smile, coo, babble, and use words during the appropriate age ranges. Once children reach school age, poor school achievement may help identify those who have an intellectual disability, but this is not a defining trait. Psychometric tests appropriate to the age of the children will help with diagnosis.

Classification of the degree of intellectual disability is never absolutely clear, and there has been debate about the value of classifying or labeling persons in this way. On one hand, it is important for professionals to understand the level of disability and to determine what kind of education and treatment would be appropriate and helpful to each individual. On the other hand, such classification can lead to low self-esteem, rejection by peers, and low expectations from teachers and parents.

There has been a marked change in the terminology used in classifying intellectual disability from the early days of its study. In the early twentieth century, the terms used for moderate, severe, and profound disability were “moron,” “imbecile,” "retard," and “idiot.” In Great Britain, the term “feeble-minded” was used to indicate moderate intellectual disability. These terms are no longer used by professionals working with the intellectually disabled. “Idiot” was the classification given to the most profoundly disabled until the middle of the twentieth century. Historically, the word has changed in meaning, from William Shakespeare’s day, when the court jester was called an idiot, to an indication of psychosis, and later to define the lowest grade of mental deficiency. The term “idiocy” has been replaced with the expression “profound intellectual disability.”

Determining the cause of intellectual disability is much more difficult than might be expected. More than a thousand different disorders that can cause intellectual disability have been reported. Some cases seem to be entirely hereditary, others to be caused by environmental stress, and others the result of a combination of the two. Frequently, the cause cannot be established. The largest proportion of the intellectually disabled population have a mild disability, and their conditions seem to be primarily due to recessive genetic traits with no accompanying physical abnormalities. From a medical standpoint, intellectual disability is considered to be a result of disease or biological defect and is classified according to its cause. Some of these causes are infections, toxins, environmental trauma, nutritional deficiencies, metabolic abnormalities, and malformation.

Infections are especially harmful to brain development if they occur in the first of pregnancy. Rubella is a viral infection that often results in intellectual disability. Syphilis is a sexually transmitted disease (STD) that affects both adults and any infants born to them, resulting in progressive mental degeneration.

Poisons such as mercury, lead, and have very damaging effects on the developing brain. More recent concerns about mercury in the diets of those who frequently consume fish and other seafood have encouraged some individuals, such as pregnant women, to change their dietary behavior in an effort to avoid potential harm to fetal development. Lead-based paints linger in older houses and are even on toys, causing in children or otherwise affecting the mental functioning of all persons in the home. Children may mouth or suck on these lead-painted toys, or they may eat chipped house paint and plaster or put them in their mouths; all of these actions could potentially cause intellectual disability, cerebral palsy, and convulsive and behavioral disorders as a result of lead exposure.

Traumatic environmental effects that can cause intellectual disability include prenatal exposure to x-rays, lack of oxygen to the brain, or a mother’s fall during pregnancy. During birth itself, the use of forceps can cause brain damage, and labor that is too brief or too long can cause mental impairment. After the birth process, head or high temperature can affect brain function.

Poor nutrition and inborn metabolic disorders may cause defective mental development because vital body processes are hindered. One of these conditions, for which every newborn is tested, is phenylketonuria (PKU), in which the body cannot process the amino acid phenylalanine. If PKU is detected in infancy, subsequent intellectual disability can be avoided by placing the child on a carefully controlled diet, thus preventing buildup of toxic compounds that would be harmful to the brain.

The failure of the neural tube to close in the early development of an embryo may result in anencephaly (an incomplete brain or none at all), hydrocephalus (an excessive amount of cerebrospinal fluid), or spina bifida (an incomplete vertebra, which leaves the exposed). Anencephalic infants live only a few hours. About half of those with other neural tube disorders will survive, usually with some degree of intellectual disability. Research has shown that if a mother’s diet has sufficient quantities of folic acid, neural tube closure disorders will be rare or nonexistent.

Microcephaly is another physical defect associated with intellectual disability. In this condition, the head is abnormally small because of inadequate brain growth. Microcephaly may be inherited or caused by maternal infection, drugs, irradiation, or lack of oxygen at birth.

Abnormal chromosome numbers are not uncommon in developing embryos and will cause spontaneous abortions in most cases. Those babies that survive usually demonstrate varying degrees of intellectual disability, and incidence increases with maternal age. A well-known example of a chromosomal disorder is Down syndrome, in which there is an extra copy of the twenty-first chromosome. Gene products caused by the extra chromosome cause intellectual disability and other physical problems. Other well-studied chromosomal abnormalities involve the sex chromosomes. Both males and females may be born with too many or too few sex chromosomes, which often results in intellectual disability.

Mild intellectual disability with no other noticeable problems has been found to run in certain families. The condition is probably a result of genetic factors interacting with environmental ones. It occurs more often in the lower economic strata of society, perhaps due in part to a family's financial situation limiting access to health care during pregnancy or infancy. It has been found that culturally deprived children have a lower level of intellectual function because of decreased stimuli as the infant brain develops.

Treatment and Therapy

Treatment and therapy for people with intellectual disabilities should be tailored to the individual, aided by a clinical determination of the severity level of the disability. Individuals with a mild to moderate disability need a modified school curriculum, along with appropriately qualified and experienced teachers. Activities should include some within their special class and some in which they interact with students of other classes. The amount of time spent in regular classes and in special classes should be determined by individual needs in order to achieve the goals and objectives planned for each. Individual development must be the primary concern.

For moderate to severely disabled individuals, the differences will be in the areas of emphasis, level of attainment projected, and methods used. The programs should consist of small classes that may be held within the public schools or outside with the help of parents and other concerned groups. These individuals will need a developmental curriculum that promotes personal development, independence, and social skills. Persons trained in special education will be needed to effectively guide their experiences in physical, social, and emotional development.

Individuals with profound intellectual disability will not be able to learn how to live independently or care for themselves. They will need almost constant care and supervision throughout their lives, and their ability to communicate will be limited. They are also more prone to associated medical conditions.

A systematic approach in special education has proven to be the best teaching method to make clear to students what behaviors will result in the successful completion of goals. This approach has been designed so that children work with only one concept at a time. There are appropriate remedies planned for misconceptions along the way. Progress is charted for academic skills, home-living skills, and prevocational training. Decisions on the type of academic training appropriate are not based on classification or labels, but on demonstrated ability.

One of the most important features of successful special education is the involvement of parents, who may find the task of rearing an intellectually disabled child overwhelming. They are in great need of caring support and information about their child and the implications for their future. Parental involvement gives the parents the opportunity to learn by observing how the professionals facilitate effective learning experiences for their children at school.

Counselors help parents identify problems and implement plans of action. They can also help them determine whether goals are being reached. Counselors must know about the community resources that are available to families. They can help parents find emotional reconciliation with the problems presented by their special children. It is important for parents to be able to accept the child’s limitations. They should not lavish special or different treatment on their disabled child, but rather treat the child like the other children.

Placing a child outside the home is indicated only when educational, behavioral, or medical controls are needed that cannot be provided in the home. Physicians and social workers should be able to do some counseling to supplement that of the trained counselors. Those who offer counseling should have basic counseling skills and relevant knowledge about the intellectually disabled individual and the family.

Sheltered employment provides highly controlled working conditions, helping individuals to become contributing members of society. This arrangement benefits the individual, the family, and society as the individual experiences the satisfaction and dignity of work. The greater the degree of intellectual disability, the more likely shelter will be required on a permanent basis. For the workshop to be successful, those in of it must consider both the personal development of the disabled worker and the business production and profit of the workshop. Failure to consider the business success of these ventures has led to failures of the programs.

There has been a trend toward deinstitutionalizing the intellectually disabled and to relocate as many residents as possible into appropriate community homes. Success will depend on a suitable match between the individual and the type of home provided. This approach is most effective if the staff of a facility is well trained and there is a fair amount of satisfactory interaction between staff and residents. It is important that residents not be ignored, and they must be monitored for proper evaluation at each step along the way. Top priority must be given to preparation of the staff to work closely with the residents.

In the past, there was no way to know before a child’s birth if there would be abnormalities. With advances in technology, however, various prenatal tests can be done, and many fetal abnormalities can be detected. Genetic counseling is important for persons who have these tests conducted. Some parents are tested before a child is conceived; others do so afterward. Tests can be done on the fetal blood and tissues that will reveal chromosomal abnormalities or inborn metabolic errors.

Many parents do not seek testing or because of the stress and that may result. Though most prenatal tests result in normal findings, if problems are indicated the parents are faced with what may be a difficult decision: whether to continue the pregnancy. It is often impossible to predict the extent of an abnormality, and weighing the sanctity of life in relation to the quality of life may present an ethical and religious dilemma. Others prefer to know what problems lie ahead and what their options are.

Finally, it is important to realize that problems such as intellectual disability may not occur in isolation from other problems. Concurrent physical and mental illnesses may add complexity to managing treatment and services for individuals with more than one condition. Assessment to rule out other conditions remains an important step in ongoing and evolving care for individuals with intellectual disability and similar conditions.

Perspective and Prospects

Throughout history, the people with intellectual disabilities were first ignored, and then subjected to ridicule. The first attempts to educate were initiated in France in the mid-nineteenth century. Shortly afterward, institutions began to spring up in Europe and the United States. These were often in remote rural areas, separated from the communities nearby, and were usually ill-equipped and understaffed. The institutions were quite regimented, and harsh discipline was kept. Meaningful interactions usually did not occur between the patients and the staff.

The medical approach of the institutions was to treat the outward condition of the intellectually disabled and ignore them as people. No concern for their social and emotional needs was shown. There were no provisions for children to play, nor was there concern for the needs of the family of those with mental handicaps.

In the nineteenth century, the first classes for the education of students with intellectual disabilities were set up in some US public schools. The first half of the twentieth century brought about the expansion of the public school programs for individuals with both mild and moderate intellectual disability. After World War II, perhaps in response to the slaughter of intellectually disabled persons in Nazi Germany, strong efforts were made to provide educational, medical, and recreational services for the intellectually disabled.

Groundbreaking research in the 1950s led to the normalization of society’s attitude about people with intellectual disabilities in the United States. Plans to help these individuals live as normal a life as possible were made. Several national organizations in the 1950s and 1960s had a strong influence on public opinion. In 1961, US president John F. Kennedy appointed a panel and instructed it to prepare a plan for the United States to help meet the complex problems of the intellectually disabled. The panel presented ninety recommendations in the areas of research, prevention, medical services, education, law, and local and national organization. Further presidential commissions on the topic were appointed and have had far-reaching effects on the well-being of people with intellectual disabilities.

A declaration of rights was adopted by the General Assembly of the United Nations in 1971, and the Education for All Handicapped Children Act was passed in the United States in 1975, providing for the development of educational programs appropriate for all handicapped and disabled children and youth. These pieces of legislation were milestones in the struggle to improve learning opportunities for the intellectually disabled.

In 2010, US president Barack Obama signed legislation requiring the federal government to replace the terms "mental retardation" and "mentally retarded" with "intellectual disability" and "intellectually disabled." Under this legislation, known as Rosa's Law, these phrases would be removed from all federal health, labor, and education policy. The DSM-5 and DSM-5-TR also changed the wording for this condition from "mental retardation," as it was known in previous edition, to "intellectual disability" and "intellectual developmental disorder."

Changes continue to take place in attitudes toward greater integration of the intellectually disabled into schools and the community, leading to significant improvements. The role of the family has increased in emphasis, for it has often been the families themselves that have worked to change old, outdated policies and reduce the stigma associated with the condition. The cooperation of the family is vital to improving the social and intellectual development of the intellectually disabled child. Because so many new and innovative techniques have been used, it is essential that programs be evaluated and compared to one another to determine which methods provide the best training and education.

Bibliography

Atkinson, Stacey, et al., editors. Intellectual Disability in Health and Social Care. Routledge, 2015.

Diament, Michelle. "Obama Signs Bill Replacing 'Mental Retardation' with 'Intellectual Disability.'" Disability Scoop, 5 Oct. 2010, www.disabilityscoop.com/2010/10/05/obama-signs-rosas-law/10547/. Accessed 23 Aug. 2024.

Dudley, James R. Confronting the Stigma in Their Lives: Helping People with a Mental Retardation Label. Charles C Thomas, 1997.

"Intellectual Developmental Disorder (Intellectual Disability)." American Psychiatric Association, 2022, www.psychiatry.org/getmedia/497935b7-4543-4343-af1e-797063c22191/APA-DSM5TR-IntellectualDisability.pdf. Accessed 23 Aug. 2024.

"Intellectual Disability." American Association on Intellectual and Developmental Disabilities, 2024, aaidd.org/intellectual-disability. Accessed 23 Aug. 2024.

Mauro, Tony. "Court Throws Out 'Mental Retardation.'" USA Today, 1 June 2014, www.usatoday.com/story/opinion/2014/06/01/hall-florida-mental-retardation-intellectual-disability-supreme-court-column/9848687/. Accessed 23 Aug. 2024.

National Academies of Sciences, Engineering, and Medicine. Mental Disorders and Disabilities Among Low-Income Children. National Academies Press, 2015.

Richards, Stephen B., et al. Cognitive and Intellectual Disabilities: Historical Perspectives, Current Practices, and Future Directions. Routledge, 2015.

Tassé, Marc J. "Defining Intellectual Disability: Finally We All Agree . . . Almost." Spotlight on Disability Newsletter, American Psychological Association, Sept 2016, d21royfkw9g4l6.cloudfront.net/Defining‗intellectual‗disability‗‗Finally‗we‗all‗agree‗‗‗‗almost‗63TROS.pdf. Accessed 23 Aug. 2024.