Mental retardation is a generalized, triarchic disorder, characterized by subaverage cognitive functioning and deficits in two or more adaptive behaviors with onset before the age of 18. Once focused almost entirely on cognition, the definition now includes both a component relating to mental functioning and one relating to the individual's functional skills in their environment.
The term "mental retardation" is a diagnostic term designed to capture and standardize a group of disconnected categories of mental functioning such as "idiot
", and "moron
" derived from early IQ tests, which acquired pejorative connotations in popular discourse over time. The term "mental retardation" has itself now acquired some pejorative and shameful connotations over the last few decades due to the use of "retarded" as an insult among younger people. This may in turn have contributed to its replacement with expressions such as "mentally challenged" or "intellectual disability".
- In North America mental retardation is subsumed into the broader term developmental disability, which also includes epilepsy, autism, cerebral palsy and other disorders that develop during the developmental period (birth to age 18.) Because service provision is tied to the designation developmental disability, it is used by many parents, direct support professional, and physicians. However, in school-based settings, the more specific term mental retardation is still typically used, and is one of 13 categories of disability under which children may be identified for special education services under Public Law 108-446.
- The phrase intellectual disability is increasingly being used as a synonym for people with significantly below-average cognitive ability. These terms are sometimes used as a means of separating general intellectual limitations from specific, limited deficits as well as indicating that it is not an emotional or psychological disability. Intellectual disability may also used to describe the outcome of traumatic brain injury or lead poisoning or dementing conditions such as Alzheimer's disease. It is not specific to congenital disorders such as Down syndrome.
The American Association on Mental Retardation continued to use the term mental retardation until 2006. In June 2006 its members voted to change the name of the organization to the "American Association on Intellectual and Developmental Disabilities," rejecting the options to become the AAID or AADD. Part of the rationale for the double name was that many members worked with people with pervasive developmental disorders, most of whom are not mentally retarded.
In the UK, "mental handicap" had become the common medical term, replacing "mental subnormality" in Scotland and "mental deficiency" in England and Wales, until Stephen Dorrell, Secretary of State for Health for the United Kingdom from 1995-7, changed the NHS's designation to "learning disability." The new term is not yet widely understood, and is often taken to refer to problems affecting schoolwork (the American usage): which are known in the UK as "learning difficulties." British social workers may use "learning difficulty" to refer to both people with MR and those with conditions such as dyslexia.
In England and Wales the Mental Health Act 1983 defines "mental impairment" and "severe mental impairment" as "a state of arrested or incomplete development of mind which includes significant/severe impairment of intelligence and social functioning and is associated with abnormally aggressive or seriously irresponsible conduct on the part of the person concerned. As behavior is involved, these are not necessarily permanent conditions: they are defined for the purpose of authorising detention in hospital or guardianship. However, English statute law uses "mental impairment" elsewhere in a less well-defined manner—e.g. to allow exemption from taxes—implying that mental retardation without any behavioural problems is what is meant. Mental Impairment is scheduled to be removed from the Act when it is amended in 2008.
Children with mental retardation 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 mental retardation may also exhibit the following characteristics:
The limitations of cognitive functioning will cause a child with mental retardation 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 mild mental retardation (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 mental retardation from learning disability or emotional/behavioral disorders. As individuals with mild mental retardation reach adulthood, many learn to live independently and maintain gainful employment.
Moderate mental retardation (IQ 50–60) is nearly always apparent within the first years of life. Children with moderate mental retardation 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 a more severe mental retardation will need more intensive support and supervision his or her entire life.
According to the latest edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-IV), there are three criteria before a person is considered to have a mental retardation: an IQ
below 70, significant limitations in two or more areas of adaptive behavior
(as measured by an adaptive behavior rating scale, i.e. communication, self-help skills, interpersonal skills, and more), and 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, it is important for the evaluator to rule them out prior to concluding that measured IQ is "significantly below average".
The following ranges, based on the Wechsler Adult Intelligence Scale (WAIS), were favored at one time, but are rarely used now:
|| IQ |
|Profound mental retardation
|| Below 20
|Severe mental retardation
|Moderate mental retardation
|Mild mental retardation
|Borderline mental retardation
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:
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 is due to traumatic injuries that damaged the brain.
, fetal alcohol syndrome
and Fragile X syndrome
are the three most common inborn causes. However, doctors have found many other causes. The most common are:
- Genetic conditions. Sometimes disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. The most prevalent genetic conditions include Down syndrome, Klinefelter syndrome, Fragile X syndrome, Neurofibromatosis, Hypothyroidism congenital, Williams syndrome, Phenylketonuria, Prader-Willi syndrome. Other genetic conditions include Phelan-McDermid syndrome (22q13del), Mowat-Wilson syndrome, genetic ciliopathy and phenylketonuria (PKU).
- Problems during pregnancy. Mental disability can result when the fetus does not develop inside the mother properly. For example, there may be a problem with the way the fetus's cells divide as it grows. A woman who drinks alcohol (see fetal alcohol syndrome) or gets an infection like rubella during pregnancy may also have a baby with mental disability.
- Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, he or she may have developmental disability due to brain damage.
- Health problems. Diseases like whooping cough, measles, or meningitis can cause mental disability. It can also be caused by not getting enough medical care, or by being exposed to poisons like lead or mercury.
- Iodine deficiency, affecting approximately 2 billion people worldwide, is the leading preventable cause of mental 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.
- Very rare conditions that are X/Y linked. In girls it can be 48, XXXX (only affecting 100 women worldwide), 49, XXXXX (only affecting 25 women worldwide) syndrome's. In boys it can be 46, XYY, 49, XXXXY, or 49, XYYYY.
Treatment and assistance
By most definitions mental retardation is more accurately considered a disability rather than a disease. MR 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.
There are thousands of agencies in the United States that provide assistance for people with developmental disabilities. They include state-run, for-profit, and non-profit, privately run agencies. Within one agency there could be departments that 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, and many more. 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.
Although there is no specific medication for mental retardation, many people with developmental disabilities have further medical complications and may take several medications. Beyond that there are specific programs that people with developmental disabilities can take part in wherein they learn basic life skills. These "goals" may take a much longer amount of time for them to accomplish, but the ultimate goal is independence. This may be anything from independence in tooth brushing to an independent residence. 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.
Several traditional terms denoting varying degrees of mental deficiency long predate psychiatry
, but have since been subject to the euphemism treadmill
. In common usage they are simple forms of abuse. 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
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.
- Cretin is the oldest and comes 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, in which there is some degree of mental retardation.
- 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 mental retardation.
- Imbecile indicated an intellectual disability less extreme than idiocy and not necessarily inherited. It is now usually subdivided into two categories, known as severe mental retardation and moderate 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".
- In the field of special education, educable (or "educable mentally retarded") refers to MR students with IQs of approximately 50-75 who can progress academically to a late elementary level. Trainable (or "trainable mentally retarded") refers to students whose IQs fall below 50 but who are still capable of learning personal hygiene and other living skills in a sheltered setting, such as a group home. In many areas, these terms have fallen out of favor in favor of "severe" and "moderate" mental retardation. While the names change, the meaning stays roughly the same in practice.
- Usage has changed over the years, and differed from country to country, which needs to be borne in mind when looking at older books and papers. For example, "mental retardation" in some contexts covers the whole field, but used to apply to what is now the mild MR group. "Feeble-minded" used to mean mild MR in the UK, and once applied in the US to the whole field. "Borderline MR" is not currently defined, but the term may be used to apply to people with IQs in the 70s. People with IQs of 70 to 85 used to be eligible for special consideration in the US public education system on grounds of mental retardation.
- Along with the changes in terminology, and the downward drift in acceptability of the old terms, 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.