Intellectual disability

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Intellectual disability (ID) is a developmental disability. It involves significant limitations both in intellectual functioning and in adaptive behavior, which covers many everyday social and practical skills.

People who acquired intellectual difficulties (e.g. through traumatic brain injury or lead poisoning) are diagnosed with neurocognitive disorder under the DSM-5.

Intellectual disabilities is now the preferred term for the concepts previously covered under ^{[citation needed]}:

• Developmental disabilities
• Learning disability in the British sense.
• Mental deficiency
• Mental handicap
• Mental retardation
• Mental subnormality

Signs

Children with ID may learn to sit up, to crawl, or to walk later than other children, or they may learn to talk later. Both adults and children with ID may also exhibit the following characteristics:

• Delays in oral language development
• Deficits in memory skills
• Difficulty learning social rules
• Difficulty with problem solving skills
• Delays in the development of adaptive behaviors such as self-help or self-care skills
• Lack of social inhibitors.

The limitations of cognitive functioning will cause a child with ID to learn and develop more slowly than a typical child. Children may take longer to learn language, develop social skills, and take care of their personal needs such as dressing or eating. Learning will take them longer, require more repetition, and skills may need to be adapted to their learning level. Nevertheless, virtually every child is able to learn, develop and become participating members of the community.

In early childhood borderline intellectual disability (IQ 71-84) and mild intellectual disability (IQ 60–70) may not be obvious, and may not be identified until children begin school. Even when poor academic performance is recognized, it may take expert assessment to distinguish mild ID from learning disability or emotional/behavioral disorders. As individuals with mild ID reach adulthood, many learn to live independently and maintain gainful employment.

Moderate intellectual disability (IQ 50–60) is nearly always apparent within the first years of life. Children with moderate ID will require considerable supports in school, at home, and in the community in order to participate fully. As adults they may live with their parents, in a supportive group home, or even semi-independently with significant supportive services to help them, for example, manage their finances.

A person with severe intellectual disability or profound intellectual disability will need lifelong intensive support and supervision.

Diagnosis

The DSM-5 describes 3 criteria for intellectual disability:

1. An IQ below 70
2. Significant limitations in two or more areas of adaptive behavior (as measured by an adaptive behavior rating scale, i.e. communication, social skills, personal independence at home or in community settings, and school/work functioning)
3. Evidence that the limitations became apparent before the age of 18

It is formally diagnosed by professional assessment of intelligence and adaptive behavior.

IQ below 70

The first English-language IQ test, the Terman-Binet, was adapted from an instrument used to measure potential to achieve developed by Binet in France. Terman translated the test and employed it as a means to measure a person's intellectual capacity based on their oral language, vocabulary, numerical reasoning, memory, motor speed and analysis skills. The mean score on the currently available IQ tests is 100, with a standard deviation of 15 (WAIS/WISC-IV) or 16 (Stanford-Binet).

Sub-average intelligence is generally considered to be present when an individual scores two standard deviatons below the test mean. Factors other than cognitive ability (depression, anxiety, etc.) can contribute to low IQ scores. The evaluator should rule them out prior to concluding that measured IQ is "significantly below average".

The following ranges, based on Standard Scores of intelligence tests, reflect the categories of the [[American Association of Mental Retardation], the Diagnostic and Statistical Manual of Mental Disorders]-IV-TR, and the International Classification of Diseases-10:

Class	IQ
Profound intellectual disability	Below 20
Severe intellectual disability	20–34
Moderate intellectual disability	35–49
Mild mental intellectual disability	50–69
Borderline intellectual functioning	70–79

Since the diagnosis is not based only on IQ scores, but must also take into consideration the person's adaptive functioning, the diagnosis is not made rigidly. It encompasses intellectual scores, adaptive functioning scores from an adaptive behavior rating scale based on descriptions of known abilities provided by someone familiar with the person, and also the observations of the assessment examiner who is able to find out directly from the person what he or she can understand, communicate, and the like.

Significant limitations in two or more areas of adaptive behavior

Adaptive behavior, or adaptive functioning, refers to the skills needed to live independently (or at the minimally acceptable level for age). To assess adaptive behavior, professionals compare the functional abilities of a child to those of other children of similar age. To measure adaptive behavior, professionals use structured interviews, with which they systematically elicit information about the person's functioning in the community from someone who knows them well. There are many adaptive behavior scales, and accurate assessment of the quality of someone's adaptive behavior requires clinical judgment as well. Certain skills are important to adaptive behavior, such as:

• daily living skills, such as getting dressed, using the bathroom, and feeding oneself;
• communication skills, such as understanding what is said and being able to answer;
• social skills with peers, family members, spouses, adults, and others.

Evidence that the limitations became apparent in childhood

This third condition is used to distinguish it from dementing conditions such as Alzheimer's disease or traumatic injuries that damaged the brain.

Causes

Psychosocial intellectual disability

The lack of mental stimulation and other forms of parental neglect during the early years of development can have severe long-term consequences on intellectual performance.

Genetic and inborn causes

Down syndrome, fetal alcohol syndrome and Fragile X syndrome are the three most common inborn causes. However, doctors have found many other causes, both genetic and other. The most common are:

• Down syndrome
• Congenital hypothyroidism
• Hydrocephaly
• Klinefelter's syndrome
• Microcephaly
• Neurofibromatosis
• Phenylketonuria (PKU)
• Prader-Willi syndrome
• Rett syndrome
• Williams syndrome

Genetic conditions may be inherited from parents or appear de novo (i.e., due to variances in genes combining/interacting).

X-linked intellectual disability

Main article: X-linked mental retardationDifferences in the X chromosome can lead to intellectual disability.

• Coffin-Lowry syndrome
• Fragile X syndrome
• MASA syndrome
• Rett syndrome
• X-linked alpha thalassemia mental retardation syndrome

Other genetic conditions include:

• Phelan-McDermid syndrome (22q13del)
• Mowat-Wilson syndrome
• Genetic ciliopathy.
• Sex chromosome conditions due to variations in the X or Y chromosome
• Different amounts of sex chromosomes: 48, XXXX and 49, XXXXX syndrome for X-only syndromes, with 47, XYY, 49, XXXXY, or 49, XYYYY for syndromes with both X and Y chromosomes

Issues during pregnancy

Intellectual disability can be caused by agents that affect how the fetus develops. For example, there may be a problem with the way the fetus's cells divide as it grows.

Drinking alcohol (see fetal alcohol syndrome) or experiencing infections like like rubella during pregnancy may also cause intellectual disability in the fetus.

Birth complications

Complications during labor and birth, such as lack of oxygen to the brain, could result in brain damage and subsequent intellectual disability.

Illness complications

Complications from diseases like whooping cough, measles, or meningitis can cause intellectual disability. This is especially likely if medical care is delayed or inadequate.

Exposure to poisons

Exposure to poisons like lead or mercury may also affect mental ability.

Nutritional deficiency

• Iodine deficiency, affecting approximately 2 billion people worldwide, is the leading preventable cause of intellectual disability in areas of the developing world where iodine deficiency is endemic. Iodine deficiency also causes goiter, an enlargement of the thyroid gland. More common than full-fledged cretinism, as retardation caused by severe iodine deficiency is called, is mild impairment of intelligence. Certain areas of the world due to natural deficiency and governmental inaction are severely affected. India is the most outstanding, with 500 million suffering from deficiency, 54 million from goiter, and 2 million from cretinism. Among other nations affected by iodine deficiency, China and Kazakhstan have begun taking action, whereas Russia has not.
• Malnutrition is a common cause of reduced intelligence in parts of the world affected by famine, such as Ethiopia.

Treatment and support

Intellectual disability is more accurately considered a disability rather than a disease. ID can be distinguished in many ways from mental illness, such as schizophrenia or depression. Currently, there is no "cure" for an established disability, though with appropriate support and teaching, most individuals can learn to do many things.

People with intellectual disabilities may benefit from:

• Occupational therapy to teach life skills, from tooth-brushing to home ownership
• Therapy or medication for co-occurring issues, such as speech disorders or mental health concerns

Various agencies provide assistance for people with intellectual and developmental disabilities. They include state-run, for-profit, and non-profit, privately run agencies.

Services for people with intellectual disabilities might include:

• Fully staffed residential homes
• Day habilitation programs that approximate schools
• Workshops wherein people with disabilities can obtain jobs
• Programs that assist people with developmental disabilities in obtaining jobs in the community
• Programs that provide support for people with developmental disabilities who have their own apartments
• Programs that assist them with raising their children

The Burton Blatt Institute at Syracuse University works to advance the civic, economic, and social participation of people with disabilities. There are also many agencies and programs for parents of children with developmental disabilities.

People with developmental disabilities learn throughout their lives and can obtain many new skills even late in life with the help of their families, caregivers, clinicians and the people who coordinate the efforts of all of these people.

Archaic terms

Various terms have been invented to describe intellectual disability. Unfortunately, most of these terms have entered popular use as insults.

Their now-obsolete use as psychiatric technical definitions is of purely historical interest. They are often encountered in old documents such as books, academic papers, and census forms (for example, the British census of 1901 has a column heading including the terms imbecile and feeble-minded).

There have been some efforts made among mental health professionals to discourage use of these terms. Nevertheless their use persists. In addition to the terms below, the abbreviation retard or tard is still used as a generic insult, especially among children and teens. A BBC survey in 2003 ranked retard as the most offensive disability-related word, ahead of terms such as spastic (not considered offensive in America) and mong.

• Abderite
• Cretin, an old term from a dialectal French word for Christian. The implication was that people with significant intellectual or developmental disabilities were "still human" (or "still Christian") and deserved to be treated with basic human dignity. This term has not been used in any serious or scientific endeavor since the middle of the 20th century and is now always considered a term of abuse: notably, in the 1964 movie Becket, King Henry II calls his son and heir a "cretin." "Cretinism" is also used as an obsolescent term to refer to the condition of congenital hypothyroidism, which can cause intellectual disability.
• Amentia has a long history, mostly associated with dementia. Amentia was for people who developed intellectual impairments early in life, while dementia was for those how developed it in adulthood. During the 1890s, amentia was used to describe someone who was born with mental deficiencies. By 1912, ament was a classification lumping "idiots, imbeciles, and feeble minded" individuals in a category separate from a dement classification, in which the onset is later in life.
• Dementia appears to be unique in that it seems to have gone unchanged in terms of meaning over hundreds of years. The term first emerged in the sixteenth century and was used in reference to people who lost mental functioning. In 1912, the classification of dement was used to identify individuals who had previously functioned normally, but who lost their faculties over time. Today's definition has pinpointed the onset of mental deterioration as occurring after the age of eighteen.
• Feeble-minded was used in the UK.
• Idiot indicated the greatest degree of intellectual disability, where the mental age is two years or less, and the person cannot guard himself or herself against common physical dangers. The term was gradually replaced by the term profound intellectual disability.
• Imbecile indicated an intellectual disability less extreme than "idiocy" and not necessarily inherited. It is now usually subdivided into two categories, known as moderate and severe mental retardation.
• Moron was defined by the American Association for the Study of the Feeble-minded in 1910, following work by Henry H. Goddard, as the term for an adult with a mental age between eight and twelve; mild mental retardation is now the term for this condition. Alternative definitions of these terms based on IQ were also used. This group was known in UK law from 1911 to 1959/60 as "feeble-minded".
• Mongolism was a medical term used to identify someone with Down syndrome. For obvious reasons, the Mongolian People's Republic requested that the medical community cease use of the term. In the 1960s, the World Health Organization agreed that the term should cease being used within the medical community.
• In the field of special education, students were sometimes called educable (IQ around 50-75, can progress academically to a late elementary level) and trainable (IQs below 50, but able to learn personal hygiene and other skills in a sheltered setting like a group home). These terms are no longer used.
• Retarded comes from the Latin retardare, "to make slow, delay, keep back, or hinder." The term was recorded in 1426 as a "fact or action of making slower in movement or time." The first record of its use in intellectual impairment was 1895. The term retarded was used to replace terms like idiot, moron, and imbecile because it was not a derogatory term. By the 1960s, however, the term had taken on a partially derogatory meaning as well.
• Mentally challenged was popular in the 80s. This term also became derogatory.
• Today, the term "retarded" is slowly being replaced by new words like "special" or "challenged." The term "developmental delay" is rapidly gaining popularity among caretakers and parents of individuals with ID. Using the word "delay" is preferred over "disability" by many people, because that term (delay) encapsulates the core deficit that creates ID in the first place. Delay suggests that a person has been held back from their potential, rather than someone who is less capable. Undoubtedly, these new terms will also gain derogatory meanings and will be replaced at some point.

Usage of terms has varied over time and in different locations.

The euphemism treadmill

The euphemism treadmill describes how neutral words can be turned into insults by people who see certain traits as degrading.

There are competing desires among elements of society. Some people want to use neutral terms to describe conditions. Others want to use such terms as weapons to insult people.

Thanks to this process, institutions of all kinds have had to repeatedly change their names. This affects the names of schools, hospitals, societies, government departments, and academic journals. For example, the Midlands Institute of Mental Subnormality became the British Institute of Mental Handicap and is now the British Institute of Learning Disability. This phenomenon is shared with mental health and motor disabilities, and seen to a lesser degree in sensory disabilities.

The only way to stop the euphemism treadmill is to teach others to view members of targeted groups with respect and empathy.

See also

• Diagnostic Adaptive Behavior Scale
• Category: Conditions with intellectual disability
• X-linked intellectual disability
• Neurodevelopmental disorders
• Savants

External links

• National Center on Birth Defects and Developmental Disabilities
• The Arc
• Special Olympics
• Mental Health Care,Inc.
• Manual published by AAIDD

References

• American Association on Intellectual and Developmental Disabilities (AAIDD). Intellectual Disability: Definition, Classification and Systems of Supports. aka as the “Definition Manual”
• Emerson E., Hatton C., Bromley, J. & Caine, A. (eds) (1998) Clinical Psychology & People with Intellectual Disabilities. Chichester:Wiley.

Intellectual disability

ICD-10	F70-F79
ICD-9	317-319
OMIM	[1]
DiseasesDB	4509
MedlinePlus	[2]
eMedicine	med/3095 neuro/605
MeSH	{{{MeshNumber}}}