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Mental retardation

Mental retardation (MR) is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors. It has historically been defined as an Intelligence Quotient score under 70. Once focused almost entirely on cognition, the definition now includes both a component relating to mental functioning and one relating to individuals’ functional skills in their environment. As a result, a person with a below-average intelligence quotient may not be considered mentally retarded. Syndromic mental retardation is intellectual deficits associated with other medical and behavioral signs and symptoms. Non-syndromic mental retardation refers to intellectual deficits that appear without other abnormalities.

Signs and symptoms

The signs and symptoms of mental retardation are all behavioral. Most people with mental retardation do not look like they have any type of intellectual disability, especially if the disability is caused by environmental factors such as malnutrition or lead poisoning. The so-called “typical appearance” ascribed to people with mental retardation is only present in a minority of cases, all of which involve syndromic mental retardation.

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 some or all of 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

Children with mental retardation learn 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 a participating member of the community.

In early childhood, mild mental retardation (IQ 50–69, a cognitive ability about half to two-thirds of standard) 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. People with mild MR are capable of learning reading and mathematics skills to approximately the level of a typical child aged 9 to 12. They can learn self-care and practical skills, such as cooking or using the local mass transit system. As individuals with mild mental retardation reach adulthood, many learn to live independently and maintain gainful employment.

Moderate mental retardation (IQ 35–49) is nearly always apparent within the first years of life. Speech delays are particularly common signs of moderate MR. People with moderate mental retardation need considerable supports in school, at home, and in the community in order to participate fully. While their academic potential is limited, they can learn simple health and safety skills and to participate in simple activities. 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. As adults, they may work in a sheltered workshop.

A person with severe or profound mental retardation will need more intensive support and supervision his or her entire life. They may learn some activities of daily living. Some will require full-time care by an attendant.


According to the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), three criteria must be met for a diagnosis of 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 intellectual capacity based on 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 deviations 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”.

Since the diagnosis is not based on IQ scores alone, but must also take into consideration a 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 such like. This enables diagnosis to avoid the pitfall of the Flynn Effect which is a consequence of a periodic re-calibration of average IQ (usually upwards) affecting the absolute values of the standard deviation causing some people to fall into a different IQ range as-if overnight.

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 persons’ functioning in the community from people who know 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 mental retardation from dementing conditions such as Alzheimer’s disease or due to traumatic injuries with attendant brain damage.

Mental Deficiency: Gene Mutations That Affect Learning, Memory In Children Identified

Feb. 6, 2009 – Mental deficiency is the most frequently occurring, yet least understood handicap in children. Even a mild form can lead to social isolation, bullying and require assistance with simple tasks. The most common variety, non-syndromic mental deficiency (NSMD), is defined as affecting an otherwise normal looking child.

With few physical clues in affected children to point researchers towards candidates to study, progress in identifying genetic causes of NSMD has been very slow. Yet that is beginning to change.

Jacques L. Michaud, a geneticist at the Sainte-Justine University Hospital Research Center and the Centre of Excellence in Neuromics of the Universit? de Montr?al, has led a multidisciplinary team which has identified mutations in a novel gene in children with NSMD. Their study is published in today’s issue of the New England Journal of Medicine and includes collaborators from McGill University in Canada, the National Institute of Mental Health and the Nathan S Kline Institute in the U.S. and the Universit? Paris Descartes in France.

“NSMD is a disorder that has many causes”, says Dr. Michaud. “By linking this gene to one kind of NSMD, we better understand the causes and we can work towards a way of identifying and treating this incapacitating condition”.

The identified mutations affect the function of SYNGAP1, a gene that codes for a protein involved in the development and function of the connections between brain cells, also called synapses. The disruption of this gene has been shown to impair memory and learning in mice.

A new approach

Dr. Michaud’s research team hypothesized that new mutations that arise in children – while not present in their parents – may represent a common cause of mental deficiency. “Several observations indicate that new mutations are a frequent cause of neurodevelopmental disorders, but their identification has been difficult because it requires the study of a large fraction of genes, which represents a challenging task”, says Dr. Fadi F. Hamdan, first author of the study.

In order to identify these new mutations, the team took advantage of the platform developed by the Synapse to Diseases consortium, based in Montreal, to study 500 synaptic genes in a group of children with unexplained mental deficiency. The team found that three percent of their subjects had new deleterious mutations in the SYNGAP1 gene.

“This discovery illustrates the power of novel technologies that allow researchers to study hundreds of genes in large groups of individuals, and provides validation for the use of such an approach for the exploration of neurodevelopmental disorders”, says Dr. Guy A. Rouleau, Director of Sainte-Justine Research Center and Head of the Synapse to Diseases consortium.

Impact of the discovery

Children with mutations in SYNGAP1 show strikingly similar forms of NSMD, with delays in their language and mental development and, in some cases, a mild form of epilepsy. Now that these SYNGAP1 mutations have been linked to NSMD, diagnostic tests can be offered to children with NSMD, and adapted strategies of learning can be developed. Moreover, because of the wealth of knowledge about the function of SYNGAP1, it may also be possible to design targeted pharmacological therapies that would aim at improving cognition and associated complications such as epilepsy.

Match the terms with their definitions


the mental act or process by which knowledge is acquired, including perception, intuition, and reasoning


a measure of the intelligence of an individual derived from results obtained from specially designed tests. The quotient is traditionally derived by dividing an individual’s mental age by his chronological age and multiplying the result by 100

Self care 

actions and attitudes which contribute to the maintenance of well-being and personal health and promote human development. 


lack of adequate nutrition resulting from insufficient food, unbalanced diet, or defective assimilation

Interpersonal skills

the life skills we use every day to communicate and interact with other people, both individually and in groups

Adaptive behavior 

a type of behavior that is used to adjust to another type of behavior or situation.

sheltered workshop 

an organization or environment that employs people with disabilities separately from others.


any physical disability or disadvantage resulting from physical, mental, or social impairment or abnormality

Flynn effect 

the substantial and long-sustained increase in both fluid and crystallized intelligence test scores measured in many parts of the world from roughly 1930 to the present day

syndromic intellectual disability

intellectual deficits which are associated with other medical and behavioral signs and symptoms

Fill in the gaps with the words from the box

Participate; reach; distinguish; learn; appear; measure; rule out;

1. Even when poor academic performance is recognized, it may take expert assessment to …. mild mental retardation from learning disability or emotional/behavioral disorders.

2. The first English-language IQ test, the Terman-Binet, was adapted from an instrument used to …. potential to achieve developed by Binet in France.

3. People with moderate mental retardation need considerable supports in school, at home, and in the community in order to …. fully.

4. Children with mental retardation may … to sit up, to crawl, or to walk later than other children, or they may learn to talk later.

5. As individuals with mild mental retardation … adulthood, many learn to live independently and maintain gainful employment.

6. Factors other than cognitive ability (depression, anxiety, etc.) can contribute to low IQ scores; it is important for the evaluator to … them …. prior to concluding that measured IQ is “significantly below average”.

7. Non-syndromic mental retardation refers to intellectual deficits that … without other abnormalities.

Build word partnerships

Mental; speech; problem solving; intelligence; learning; sheltered; cognitive; adaptive

Behavior; retardation; ability; quotient; skills; workshop; delays; disability

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