Associated Traits (Mental Retardation)

Some common behavioral traits associated with mental retardation, such as a low tolerance for frustration; do not appear with the criteria that must be present for diagnosis. Easily frustrated mentally retarded individuals sometimes become aggressive and may engage in self-injuries behavior. Not all mentally retarded individuals are easily frustrated, however. While some are impulsive, stubborn, and immature, others are passive and pleasant.

Other common behavioral traits include low self-esteem and difficulty sustaining attention. Co-morbid mood disorders (including depression) often accompany mental retardation. However, many mentally retarded individuals show no signs of mood disorders and appear happy and amiable.

Some individuals with mental retardation have unique physical characteristics that mark them as retarded, including being short of stature or processing unique facial characteristics associated with conditions related to their mental retardation. Others have a perfectly normal physical appearance.

Although intellectual functioning is always deficit across the entire mental retardation classification, there are fewer characteristics that uniquely identify someone as being mentally retarded. For example, there are no particular personality characteristics unique to mental retardation (although specific syndrome that causes mental retardation to occur may tend to have particular personality characteristics, e.g., children with Williams’s syndrome tend to be outgoing). The wide variety of personality characteristics displayed by people with mental retardation reflects the heterogeneity (wide differences) of that group. Their personalities are as different as the personalities in the general populations are. Some mentally retarded people are easygoing, while others are impulsive or aggressive.

Definitions of Mental Retardation:

A Chronological List with Dates and References

1. An idiot is one who hath no understanding from his nativity. Prerogative of the King of England, 1255 to 1290 A. D. (Payne and Patton, 1981)

The word idiot is derived from the Latin word idiota, meaning an ignorant person and from the Greek word idiotos, meaning unfit for public life. It was used to refer to individuals with mental retardation (of all levels) well into the 20^th Century.

2. An idiot is such a person who cannot account or number, nor can tell who was his father or mother, nor how he, so as it may appear he has not understands or reason of what shall be his profit or his loss. Sir Anthony Fitzherbert, about 1510 to 1520 (Payne and Patton, 1981).

Sir Anthony Fitzherbert was an English judge who was appointed the king’s serjeant-at-law on 18 November, 1510. His work, La Graunde Abridgement, was the first systematic attempt to provide a summary of English law.

3. Idiocy  is a specific infirmity of the cranio-spinal axis, produced by deficiency of nutrition in utero and neo-anti. It incapacitates mostly the functions which give rise to the reflex, instinctive and conscious phenomena of life; consequently, the idiot moves, feels, understands, wills but imperfectly; does nothing, thinks of nothing, cares for nothing (extreme cases), he is legally irresponsible, isolated without associations; a soul shut up in imperfect organs an innocent.

Edouard Seguin, France/United States, 1866.

Edouard Seguin was an associate of Jean Itard, whose work with Victor, the Famouse “Wild Boy of Aveyron” was the first documented (but unsuccessful) attempt to educate a child thought to have idiocy (mental retardation). Seguin became head teacher of a class of idiot children at salpetriere, France and later started a private school for idiots. He later moved to the United States, where in 1866 he published his famous work, Idiocy: and its Treatment by the Physiological Method, in which the above definition appeared. In 1876, Seguin became the first president of The Association of Medical Officers of American Institution for Idiotic and Feeble-Minded Persons, which evolved into the American Association on Mental Retardation.

4. Idiocy (involves) deficiency in the ordinary mental powers, due to disease or failure of development of the central nervous system. More especially, idiocy often relates to the severer forms of such mental deficiency, while children of subnormal capacity or backward development are spoken of as feeble-minded, or children. There is some tendency to use the term feeble-minded to include all degrees of defect from the slightest to the most severe. (James Mark Baldwin, Canada, 1901).

James Mark Baldwin founded the first psychological laboratory in the British Empire in 1889 at the University of Toronto. His most famous work, Mental Development in the Child and the Race, first published in 1895 is recognized as an important text in the history of social psychology.

5. Mental Deficiency: A state of incomplete mental development of such a kind and degree that the individual is incapable of adapting himself to the normal environment of his fellows in such a way to maintain existence independently of supervision, control or external support. (Tredgold, Great Britain, 1937).

A. F. Tredgold was a member of the Britich Eugenics Society, which like its counterpart in the United States favored reducing or eliminating reproduction by those deemed unfit through segregation and sterilization. In his article “The Feebleminded -  A Social Danger,” which appeared in Eugenics Review, (1909), Tredgold wrote, “…in the animal world or in a primitive state of human society these degenerate members would very soon by extinguished …. Our modern legislation … is actually tending to breed degenerates.” (Eugenics Watch U.K)

6. Six criteria … have been generally considered essential to an adequate definition and concept (of Mental Deficiency): These are 1) social incompetence;

2) Mental sub normality; 3) which has been developmentally arrested; 4) which obtains at maturity; 5) is of constitutional origin; and 6) is essentially incurable. E. A. Doll, United States, 1941 (Doll, 1941, p.215).                       

Edgar Doll is best known for his work at the Vineland Training School where he developed the Vineland Social Maturity Scale (now the Vineland Adaptive Behavior Scales). First published in 1935, this instrument was designed to assess the daily living skills of individuals with mental retardation.

7. Mental Retardation refers to significantly sub average general intellectual functioning which originates during the developmental period and is associated with impairment in adaptive behavior. 

Sub average intellectual Functioning: one or more standard deviations (SD’s) below the mean. (An IQ score of 85 or below)

Adaptive Behavior: adaptation to the demands of the environment.

Developmental Period: birth to age 16.

American Association on Mental Deficiency, United States, 1961 (Heber, 1961)

This definition, with its three components (sub average intelligence, impaired adaptive behavior, and origination during the developmental period), became widely accepted. Subsequent AAMD/AAMR definitions are essentially refinements of Heber’s 1961 definition.

8. Mental Retardation refers to significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period. Sub-Average Intellectual Functioning: at least two standard deviations below the mean (current functioning – not permanent status). (an IQ of 70 score or below)

Adaptive Behavior: ability to meet the standards of personal independence and social responsibility expected of his/her level and cultural group.

The 1973, definition through retaining the three basic AAMR components, makes the following significant changes:

1) defining “sub-average intelligence” as rather than one standard deviation below the mean (85). This reduced the number of individuals who met this criterion from 16% of the population to a little more than 2% of the population;

2) clarifying the meaning of deficient adaptive behavior; and

3) extending the developmental period to age 18.

9. Mental Retardation refers to significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period. Sub-average Intellectual Functioning: two or more standard deviations below average but a small number of persons with scores up to 10 points above the guideline ceiling may be classified as mildly mentally retarded if their adaptive behavior is significantly impaired (current functioning – not permanent status)

American Association on Mental Deficiency, United States, 1977 (Grossman, 1977)

This 1977 revision allows for individuals with borderline intelligence (70 to 80) to be classified as having mental retardation and thus makes them eligible for services provided to those with MR, including special education.

10. Mental Retardation refers to substantial limitations in present functioning. It is characterized by significantly sub-average general intellectual functioning existing concurrently with related limitations in two or more of the following applicable adaptive skills areas: communication, self care, home living, social skills, self direction, health and safety, functional academics, leisure and work. Mental retardation manifested before age 18.

Significantly Sub average Intellectual Functioning: same as 9 (An IQ Score of 70-80 or below)

American Association on Mental Retardation, United States, 1992 (AAMR, 1992)

This AAMR definition, through still retaining Heber’s three components, provides even more specificity regarding the meaning of the phrase “deficits in adaptive behavior.” Other changes, particularly in regard to level of mental retardation. Though not part of definition, are included in the AAMR publications, Mental Retardation: Definition, classification, and systems of supports, in which the new definition appear. Click here for an ERIC Clearing house article which summarizes differences between the current AAMR definition and previous ones.

11. Mental Retardation is a disability characterized by significant limitation both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before the age of 18.

Significant Limitations in Intellectual Functioning: same as 9.

Definition of Mental Retardation

Mental retardation is not something you have, like blue eyes, or a bad heart. Nor is it something you are, like short, or thin.

It is not a medical disorder, nor a mental disorder.

Mental retardation is a particular state of functioning that begins in childhood and is characterized by limitation in both intelligence and adaptive skills.

Mental retardation reflects the ˝fit˝ between the capabilities of individuals and the structure and expectations of their environment.

The AAMR Definition of Mental Retardation

Mental retardation is a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills.

The disability originates before age 18.

Five Assumptions Essential to the Application of the Definition

Limitations in present functioning must be considered within the context of community environments typical of the individual’s age peers and culture                                             

1. Valid assessment considers cultural and linguistic diversity as well as differences in communication, sensory, motor, and behavioral factors.                                                    
2. Within an individual, limitations often coexist with strengths.                                          
3. An important purpose of describing limitations is to develop a profile of needed supports.                                                                                                                          
4. With appropriate personalized supports over a sustained period, the life functioning of the person with mental retardation generally will improve.                         

Founded in 1876, AAMR is an international multidisciplinary association of professionals. The Association has had responsibilities for defining mental retardation since 1921.

INDIVIDUALS WITH MILD MENTAL RETARDATION

(Formerly referred to as educable):

• Are likely to need only intermittent to limited support;
• Typically do not “look” different from their non-disabled peers;
• Often have only mild or moderate developmental delays, except in academics, which is often the major area of deficit;
• Therefore, they are often not until they enter the school setting where their cognitive disability is most apparent;
• In Minnesota, students with mild MR spend most of the school day in the regular classroom;
• They typically attain 3^rd –to-6^th-grade academic achievement level by the time they finish high school;
• As adults, many, though not all, with mild MR will be able to obtain independent employment;
• Many will marry, have children, and blend rather indistinguishably into the community; for those who achieve total independence, the label of mental retardation is no longer appropriate.

Individuals with Moderate to severe Mental Retardation

(Formerly called “trainable”):

·        Will probably need limited to extensive supports;

·        They are more likely have a recognizable syndrome (such as Down Syndrome);

·        Therefore, may “look” different than their non-disabled peers;

·        Their development is often significantly delayed;

·        They are typically identified as infants or toddlers;

·        Most begin receiving special education during the preschool years;

·        They may be include in the regular classroom part of the school day (particularly here in Minnesota);

·        But often spend much of the school day in a separate classroom where they learn adaptive living skills;

·        As adults, most of  the individuals with moderate to severe MR will not achieve total independence;

·        Rather, they are likely to continue to need limited to extensive support such as that provided in group homes or semi-independent living situations (SILs); some may continue to live with their parents;

·        Some individuals with moderate to severe MR may be able to succeed in modified competitive employment situations;

·        However, many will work in supported, non-competitive setting such as sheltered workshops.

Individuals with profound Mental Retardation:

·        Will generally need services at the pervasive level, typically throughout their life;

·        They are likely to have multiple disabilities, particularly in the areas of mobility and communication;

·        Therefore, many use wheelchairs and alternate forms of communication;

·        Their communication deficits make it difficult to accurately assess their intellectual functioning;

·        In educational setting, they may be placed along with students with moderate to severe MR or in their own classroom;

·        Some adults with this level of retardation remain in institutional settings, but most currently live in group homes.

Classification and Types of Mental Retardation

Mental Retardation

Mental Retardation (MR) is a developmental disability that first appears in children under the age of 18. It is defined as a level of intellectual functioning (as measured by standard intelligence tests) that is well below average and result in significant limitations in the person's daily living skills (adaptive functioning).

Description

Mental Retardation begins in childhood or adolescence before the age of 18. In most cases, it persists throughout adult life. A diagnosis is mental retardation is made if an individual has an intellectual functioning level well below average, as well as significant limitations in two or more adaptive skill areas. Intellectual functioning level is defined by standardized tests that measure the ability to reason in terms of mental age (intellectual quotient or IQ). Mental Retardation is defined as an IQ score below 70-75. Adaptive skills is a term that refers to skills needed for daily life. Such skills include the ability to produce and understand language (communication); home-living skills; use of community resources; health, safety, leisure, self-care, and social skills; self-direction; functional academic skills (reading, writing, and arithmetic); and job-related skills.

In general, mentally retarded children reach such developmental milestones as walking and talking much later than the children in the general population. Symptoms of mental retardation may appear at birth or later in childhood. The child's age at onset depends on the suspected of the disability. Some cases of mild mental retardation are not diagnosed before the child enters preschool or kindergarten.

These children typically have difficulties with social, communication, and functional academic skills. Children who have a neurological disorder or illness such as encephalitis or meningitis may suddenly show signs of cognitive impairment and adaptive difficulties.

Mental Retardation varies in severity. The Diagnostic and Statistical Manual of Mental Disorders, fourth edition, text version (DSM-IV-TR), which is the diagnostic standard for mental health care professionals in the United States, classifies four different degrees of mental retardation: mild, moderate, severe, and profound. These categories are based on the person’s level of functioning.

Mild mental retardation

Approximately 85% of the mentally retarded population is in the mildly retarded category. Their IQ score ranges from 50-70, and they can often acquire academic skills up to about the sixth-grade level. They can become fairly self-sufficient and in some cases live independently, with community and social support.

Moderate mental retardation

About 10% of the mentally retarded population is considered moderately retarded. Moderately retarded persons have IQ scores ranging from 35-55. They can carry out work and self-care tasks with moderate supervision. They typically acquire communication skills in childhood and are able to live and function successfully with in the community in such supervised environments as group homes.

Severe mental retardation

About 3-4% of the mentally retarded population is severely retarded. Severely retarded persons have IQ scores of 20-40. They may master very basic self-care skills and some communication skills. Many severely retarded individuals are able to live in a group home.

Profound mental retardation

Only 1-2% of the mentally retarded population is classified as profoundly retarded. Profoundly retarded individuals have IQ score under 20-25.

They may be able to develop basic self-care and communication skills with appropriate support and training. Their retardation is often caused by an accompanying neurological disorder. Profoundly retarded people need a high level of structure and supervision.

The Americans Association on Mental Retardation (AAMR) has developed another widely accepted diagnostic classification system for mental retardation.

The AAMR classification system focuses on the capabilities of the retarded individual rather than on his or her limitations. The categories describe the level of support required. They are: intermittent support; limited support; extensive support; and pervasive support. To some extent, the AAMR classification mirrors the DSM-IV-TR classification. Intermittent support, for the example, is support that is needed only occasionally, perhaps during times of stress or crisis for the retarded person. It is the type of support typically required for most mildly retarded people. At the other end of the spectrum, pervasive support, or life-long, daily support for most adaptive areas, would be required for profoundly retarded persons. The AAMR classification system refers to the “below-average intellectual function” as an IQ of 70-75 or below.

CHARACTERISTICS AND SIGNIFICANCE OF MENTAL RETARDATION

Although mental retardation of any degree has profound implications for a person’s cognitive and social development, it is a condition which in many cases is not readily apparent. Which some of the mentally retarded, such as those whose retardation is caused by Down’s syndrome or fetal alcohol syndrome, have characteristically distinctive facial features, most cannot be identified by their physical appearance alone. Unless their cognitive impairment is unusually severe (e.g. an I.Q. below 40), persons with mental retardation may be thought of as slow but the full extent of their impairment is often not readily appreciated. Particularly by people who have limited contact with or knowledge of them, including police, prosecutors, judges, and other participants in the criminal justice system. Many capital offenders with mental retardation did not have their condition diagnosed until trial or during post-conviction proceedings.

A person with mental retardation, according to one expert, “is always the least smart person in any group. This leads to fear, dependence and an experience of terrible stigma and devaluation.” Since mentally retarded people are often ashamed of their own retardation, they may go to great lengths to hide their retardation, fooling those with no expertise in the subject. They may wrap themselves in a “cloak of competence” hiding their disability even from those who want to help them, including their lawyers. Overworked or incompetent lawyers may overlook evidence of retardation and fail to request a psychological evaluation or rise during trail. At times, even competent lawyers who are anxious to help their clients may fail to identify their clients’ retardation or may be unable to access funds for a physiological evaluation.

Oliver Cruz, who was executed in Texas on August 9, 2000, had an I.Q. that was measured variously at 64 and 76. Cruz nonetheless insisted to reporters that, although he was perhaps “slow in reading, slow in learning,” he was not mentally retarded.

 Mitigation specialist Scharlette Holdman recalled a client who so successfully hid his retardation from his attorneys that he allowed them to sign him up for college – level calculus classes, which he could not comprehend. He had gone through much of his schooling allowing his younger sister to complete his homework for him. When he was given papers to read in connection to his case, he would carefully stare at them. If he was asked a substantive question, he usually responded, “I don’t recall.” Only when experts in retardation evaluated him and investigators reviewed his school records and spoke to his family did lawyers discover he had mental retardation and had been considered “slow” since his early childhood.

Another capital defendant “hid his mental retardation for most of his life by working at a very repetitive job as a switcher on the railroad. He lied about finishing high school. He was actually in special education classes and is not finish the sixth grade. He was drafted into the army and discharged because of his mental retardation. He lied about his service record. He often made things up so that people would not suspect mental retardation.”

The fact that many people with mental retardation can and do live relatively “normal” lives with their families or in the community, coupled with the fact that most of them do not look different from people with average intellectual capabilities, can make it difficult for the public to appreciate the significance of their condition. But, as the late U.S. Supreme Court Justice Brennan noted, “Every individual who has mental retardation’—irrespective of his or her precise capabilities or experiences – has a substantial disability in cognitive ability and adaptive behavior.” Like all human beings, people with mental retardation deserve to be treated with dignity and respect, and deserve the chance to live lives that are as normal as possible – but they also require special acknowledgment of their vulnerabilities and their mental Incaabilities.

A person with mental retardation will have limitations of a greater or lesser extent in every aspect of cognitive functioning. He or she will have limited abilities to learn (including reading, writing and arithmetic) and to reason, plan, understand, judge, and discriminate. Mental Retardation truncates the capacity to think about intended actions, to consider their possible consequences, and to exercise restraint. One expert has summarized the attributes of mental retardation as follows:

Almost uniformly, individuals with mental retardation have grave difficulties in language and communication. They have problems with attention, memory. Intellectual rigidity, and in moral development or moral understanding. They are susceptible to suggestion and readily acquiesce to other adults or authority figures… People with mental retardation have limited knowledge because their impaired intelligence has prevented them from learning very much. They also have grave problems in logic, foresight, planning, strategic thinking, and understanding consequences.

Many of these limitations, of course, characterize children. But while children will outgrow these limitations as their brains develop and mature people with mental retardation will not.

In limitations a person’s cognitive development and ability to learn, mental retardation also limits the ability to understand abstract concepts, including moral concepts. While most defendants with mental retardation who have committed a crime know they have done something wrong, they often cannot explain why the act was wrong.

At the trial of a man with mental retardation convicted of raping and murdering and 87-year old woman, a clinical psychologist testified that while the defendant could acknowledge that rape was “wrong,” he was nonetheless not able to offer any explanation for why. “Pressed for an answer, [the defendant] admitted not receiving ‘permission’ for the rape…..Pressed further, in desperation, he blurted out, Maybe it’s against her religion!’ The jury gasped at such an explanation.

The inability to comprehend abstract concepts may include the inability to fully understand the meaning of “death” or “murder”.

Morris Mason, whose I.Q. was 62-66 was executed in 1985 in Virginia after being convicted of rape and murder. Before his execution, Mason asked one of his legal advisors for advice on what to wear to his funeral.

Robert Wayne Sawyer, who had mental retardation, was convicted of beating, raping, and burning alive a young woman in 1979. At his clemency hearing, the chair of the Louisiana pardons board asked Sawyer if he knew what murder was. Sawyer responded, “That when the breath leaves your body.” In response to a subsequent question he clarified that “it’s when you stab someone and the breath leaves the body.” When he was then asked what happens if someone is shot, Sawyer answered, “I just don’t know.”

Since they often face abuse, taunts, and rejection because of their low intelligence, people with mental retardation can be desperate for approval and friendship. Eager to be accepted and eager to please, people with mental retardation are characteristically highly suggestible.

Earl Washington, whose mental retardation was diagnosed when he was a child, confessed during long police interrogations to a murder that he did not commit. Washington was so suggestible and eager to please, according to a former employer, that “you could get [him] to confess that he walked on the moon” In an effort to show the invalidity of Washington’s confession because of his mental deficiencies, his trail lawyer would “pick a day, any day, and tell Washington that day was [his] birth date….after prodding and cajoling, Washington would accept the false date.”

As one psychiatrist testified about a capital defendant with an I.Q. of between 35 to 45: “[People with mental retardation try] to go along with people that they suspect are in authority. For example, I asked him if we were in Atlanta and he said yes, ‘we are in Atlanta.’ In fact, we were in Birmingham, Alabama. I could have said New York and he would have said ‘Sure, New York”……

Low intelligence and limited adaptive skills also mean that people with mental retardation often miss social “cues” that other adults understand. Their inappropriate social responses can be misinterpreted by people who do not know they have mental retardation or who do not understand the nature of retardation.

They may act in ways that seem suspicious, even when they have done nothing wrong. When questioned by police or other authority figures, they often smile inappropriately, fail to remain still when ordered to do so, or act agitated and furtive when they should be calm and polite. Others may fall asleep at the wrong moment.

Hebert Welcome was convicted of murdering his aunt and her boyfriend in 1981 in Louisiana. Welcome has mental retardation and, according to psychiatric testimony presented at his trial, has a mental age of eight. He smiled incessantly during his capital murder trail and almost involuntary defense mechanism developed in response to a lifetime of taunts. As his defense attorney noted, “Many people with retardation smile a lot… They are anxious for approval, and have learned that smiling is one way to get [it]. But they don’t have the judgment to know when to smile.” The prosecutor argued that Welcome’s smiles showed that he lacked remorse for his crimes. He was sentenced to death and remains today on death row.

Both Barry Lee Fairchild, capital trials—eloquent evidence of the failure of these two men with mental retardation to appreciate the significance of the criminal proceeding against them. Trail counsel was not aware that they had mental retardation. But their tendency to sleep peacefully during their trials helped alert post-conviction lawyers to their mental disability. In the case of white, who snored loudly during the penalty phase of his trial, the prosecutor argued that his conduct indicated his lack of remorse for his crime and his lack of respect for the criminal justice system. Both Fairchild and White were sentenced to death and executed.

CAUSES AND SYMPTOMS (Mental Retardation)

Low IQ scores and limitations in adaptive skills are the hallmarks of mental retardation. Aggression, self-injury, and mood disorders are sometimes associated with the disability. The severity of the symptoms and the age at which they first appear depend on the cause. Children who are mentally retarded reach developmental milestones significantly later than expected, if at all. If retardation is caused by chromosomal or other generic disorders, it is often apparent from infancy. If retardation is caused by childhood illness or injuries, learning and adaptive skills that were once easy may suddenly become difficult or impossible to master.

In about 40% of cases, the cause of mental retardation cannot be found. Biological and environmental factors that can cause mental retardation include:

Genetic Factors

About 30% of cases of mental retardation is caused by hereditary factors. Mental retardation may be caused by an inherited genetic abnormality, such as fragile X syndrome. Fragile X, a defect in the chromosome that determines sex, is the most common inherited cause of mental retardation. Single-gene defects such as phenylketonuria (PKU) and other inborn errors of metabolism may also cause mental retardation if they are not discovered and treated early. An accident or mutation in genetic development may also cause retardation. Example of such accidents is development of an extra.

An accident or mutation in genetic development may cause retardation. An example of such a mutation is the development of an extra chromosome 21 that cause Down syndrome.

Prenatal illness and issues

Fetal alcohol syndrome (FAS) affects one in 3,000 children in Western countries. It is caused by the mother’s heavy drinking during the first twelve weeks (trimester) of pregnancy. Some studies have shown that even moderate alcohol use during the pregnancy may cause learning disabilities in children. Drug abuse and cigarette smoking during pregnancy have also been linked to mental retardation.

Maternal infections and such illness as glandular disorders, rubella, toxoplasmosis, and cytomegalovirus (CMV) infection may cause mental retardation. When the mother has high blood pressure (hypertension) or blood poising (toxemia), the flow of oxygen to the fetus may be reduced, causing Brain damage and mental retardation.

Birth defects that cause physical deformities of the head, brain, and central nervous system frequently cause mental retardation. Neural tube defect, for example, is a birth defect in which the neural tube that forms the spinal cord does not close completely. This defect may cause children to develop an accumulation of cerebrospinal fluid inside the skull (hydrocephalus). Hydrocephalus can cause learning impairment by putting pressure on the brain.

Childhood illness and injuries

Hyperthyroidism, whooping cough, chickenpox, measles, and Hib disease

(A bacterial infection) may cause mental retardation if they are not treated adequately. An infection of the membrane conversing the brain (meningitis)

or an inflammation of the brain itself (encephalitis) can cause swelling that in turn may cause brain damage and mental retardation. Traumatic brain injury caused by a blow to the head or by violent shaking of the upper body may also cause brain damage and mental retardation in children.

Environmental factors

Ignored or neglected infants who are not provided with mental retardation and physical stimulation required for normal development may suffer irreversible learning impairment. Children who live in poverty and suffer from malnutrition, unhealthy living conditions, abuse, and improper or inadequate medical care are at a higher risk. Exposure to lead or mercury can also cause mental retardation. Many children have developed lead poisoning from eating the flaking lead-based paint often found in older building.