Mental retardation, also known as intellectual disability, is a developmental disability characterized by limitations in intellectual functioning (IQ under 70-75) and adaptive behaviors that are diagnosed before age 18. It occurs in approximately 2-3% of the population and can be caused by genetic, prenatal, childhood, and environmental factors. Mental retardation is classified by severity into four categories: mild, moderate, severe, and profound. Treatment focuses on education, life skills training, supportive living, and family therapy.

1. Mental retardation or intellectual disability, (MR/ID), exists in children whose brains do not
develop properly or function within the normal range. There are four levels of retardation:
mild, moderate, severe, and profound.
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2. Mental Retardation
Definition
Mental retardation is a developmental disability that first appears in children under the age of 18. It is defi
ned as anintellectual functioning level (as measured by standard tests for intelligence quotient) that is well
below average andsignificant limitations in daily living skills (adaptive functioning).
Description
Mental retardation occurs in 2.5-3% of the general population. About 6-
7.5 million mentally retarded individuals live in theUnited States alone. Mental retardation begins in childh
ood or adolescence before the age of 18. In most cases, itpersists throughout adulthood. A diagnosis of
mental retardation is made if an individual has an intellectual functioninglevel well below average and sign
ificant limitations in two or more adaptive skill areas. Intellectual functioning level isdefined by standardize
d tests that measure the ability to reason in terms of mental age (intelligence quotient or IQ).Mental retard
ation is defined as IQ score below 70-
75. Adaptive skills are the skills needed for daily life. Such skillsinclude the ability to produce and underst
and language (communication); home-
living skills; use of community resources;health, safety, leisure, self-care, and social skills; self-
direction; functional academic skills (reading, writing, andarithmetic); and work skills.
In general, mentally retarded children reach developmental milestones such as walking and talking much
later than thegeneral population. Symptoms of mental retardation may appear at birth or later in childhood
. Time of onset depends onthe suspected cause of the disability. Some cases of mild mental retardation a
re not diagnosed before the child enterspreschool. These children typically have difficulties with social, co
mmunication, and functional academic skills. Childrenwho have a neurological disorder or illness such as
encephalitis or meningitis may suddenly show signs of cognitiveimpairment and adaptive difficulties.
Mental retardation varies in severity. The Diagnostic and Statistical Manual of Mental Disorders, Fourth E
dition (DSM-
IV)is the diagnostic standard for mental healthcare professionals in the United States. The DSM-
IV classifies four differentdegrees of mental retardation: mild, moderate, severe, and profound. These cat
egories are based on the functioning levelof the individual.
Mild mental retardation
Approximately 85% of the mentally retarded population is in the mildly retarded category. Their IQ score r
anges from 50-
75, and they can often acquire academic skills up to the 6th grade level. They can become fairly self-
sufficient and insome cases live independently, with community and social support.
Moderate mental retardation
About 10% of the mentally retarded population is considered moderately retarded. Moderately retarded in
dividuals haveIQ scores ranging from 35-55. They can carry out work and self-
care tasks with moderate supervision. They typicallyacquire communication skills in childhood and are abl
e to live and function successfully within the community in asupervised environment such as a group hom
e.

3. Severe mental retardation
About 3-
4% of the mentally retarded population is severely retarded. Severely retarded individuals have IQ scores
of 20-40. They may master very basic self-
care skills and some communication skills. Many severely retarded individuals areable to live in a group h
ome.
Profound mental retardation
Only 1-
2% of the mentally retarded population is classified as profoundly retarded. Profoundly retarded individual
s haveIQ scores under 20-25. They may be able to develop basic self-
care and communication skills with appropriate supportand training. Their retardation is often caused by a
n accompanying neurological disorder. The profoundly retarded need ahigh level of structure and supervi
sion.
The American Association on Mental Retardation (AAMR) has developed another widely accepted diagno
sticclassification system for mental retardation. The AAMR classification system focuses on the capabilitie
s of the retardedindividual rather than on the limitations. The categories describe the level of support requ
ired. They are: intermittentsupport, limited support, extensive support, and pervasive support. To some ex
tent, the AAMR classification mirrors theDSM-
IV classification. Intermittent support, for example, is support needed only occasionally, perhaps during ti
mes ofstress or crisis. It is the type of support typically required for most mildly retarded individuals. At th
e other end of thespectrum, pervasive support, or life-
long, daily support for most adaptive areas, would be required for profoundly retardedindividuals.
Causes and symptoms
Low IQ scores and limitations in adaptive skills are the hallmarks of mental retardation. Aggression, self-
injury, andmood
disorders are sometimes associated with the disability. The severity of the symptoms and the age at whi
ch theyfirst appear depend on the cause. Children who are mentally retarded reach developmental milest
ones significantly laterthan expected, if at all. If retardation is caused by chromosomal or other genetic dis
orders, it is often apparent frominfancy. If retardation is caused by childhood illnesses or injuries, learning
and adaptive skills that were once easy maysuddenly become difficult or impossible to master.
In about 35% of cases, the cause of mental retardation cannot be found. Biological and environmental fac
tors that cancause mental retardation include:
Genetics
About 5% of mental retardation is caused by hereditary factors. Mental retardation may be caused by an i
nheritedabnormality of the genes, such as fragile X
syndrome. Fragile X, a defect in the chromosome that determines sex, isthe most common inherited cau
se of mental retardation. Single gene defects such as phenylketonuria (PKU) and otherinborn errors of
metabolism may also cause mental retardation if they are not found and treated early. An accident ormuta
tion in genetic development may also cause retardation. Examples of such accidents are development of
an extrachromosome 18 (trisomy 18) and Down
syndrome. Down syndrome, also called mongolism or trisomy 21, is caused byan abnormality in the dev
elopment of chromosome 21. It is the most common genetic cause of mental retardation.

4. Prenatal illnesses and issues
Fetal alcohol
syndrome affects one in 600 children in the United States. It is caused by excessive alcohol intake in thef
irst twelve weeks (trimester) of pregnancy. Some studies have shown that even moderate alcohol use du
ring pregnancymay cause learning disabilities in children. Drug abuse and cigarette smoking during preg
nancy have also been linkedto mental retardation.
Maternal infections and illnesses such as glandular disorders, rubella, toxoplasmosis, and cytomegalovi
rus
infectionmay cause mental retardation. When the mother has high blood pressure (hypertension) or blo
od poisoning (toxemia),the flow of oxygen to the fetus may be reduced, causing brain damage and ment
al retardation.
Birth
defects that cause physical deformities of the head, brain, and central nervous system frequently cause
mentalretardation. Neural tube defect, for example, is a birth defect in which the neural tube that forms th
e spinal cord does notclose completely. This defect may cause children to develop an accumulation of cer
ebrospinal fluid on the brain(hydrocephalus). Hydrocephalus can cause learning impairment by putting p
ressure on the brain.
Childhood illnesses and injuries
Hyperthyroidism, whooping cough, chickenpox, measles, and Hib disease (a bacterial infection) may ca
use mentalretardation if they are not treated adequately. An infection of the membrane covering the brain
(meningitis) or aninflammation of the brain itself (encephalitis) cause swelling that in turn may cause brain
damage and mental retardation.Traumatic brain injury caused by a blow or a violent shake to the head m
ay also cause brain damage and mentalretardation in children.
Environmental factors
Ignored or neglected infants who are not provided the mental and physical stimulation required for normal
developmentmay suffer irreversible learning impairments. Children who live in poverty and suffer from m
alnutrition, unhealthy livingconditions, and improper or inadequate medical care are at a higher risk. Exp
osure to lead can also cause mentalretardation. Many children have developed lead
poisoning by eating the flaking lead-based paint often found in olderbuildings.
Diagnosis
If mental retardation is suspected, a comprehensive physical
examination and medical history should be doneimmediately to discover any organic cause of symptoms
. Conditions such as hyperthyroidism and PKU are treatable. Ifthese conditions are discovered early, the
progression of retardation can be stopped and, in some cases, partiallyreversed. If a neurological cause s
uch as brain injury is suspected, the child may be referred to a neurologist orneuropsychologist for testing
.
A complete medical, family, social, and educational history is compiled from existing medical and school r
ecords (ifapplicable) and from interviews with parents. Children are given intelligence tests to measure th
eir learning abilities andintellectual functioning. Such tests include the Stanford-
Binet Intelligence Scale, the Wechsler Intelligence Scales, theWechsler Preschool and Primary Scale of I
ntelligence, and the Kaufmann Assessment Battery for Children. For infants,the Bayley Scales of Infant D
evelopment may be used to assess motor, language, and problem-

5. solving skills. Interviewswith parents or other caregivers are used to assess the child's daily living, muscle
control, communication, and socialskills. The Woodcock-
Johnson Scales of Independent Behavior and the Vineland Adaptive Behavior Scale (VABS) arefrequentl
y used to test these skills.
Treatment
Federal legislation entitles mentally retarded children to free testing and appropriate, individualized educa
tion and skillstraining within the school system from ages 3-
21. For children under the age of three, many states have establishedearly intervention programs that ass
ess, recommend, and begin treatment programs. Many day schools are available tohelp train retarded chi
ldren in basic skills such as bathing and feeding themselves. Extracurricular activities and socialprograms
are also important in helping retarded children and adolescents gain self-esteem.
Training in independent living and job skills is often begun in early adulthood. The level of training depend
s on the degreeof retardation. Mildly retarded individuals can often acquire the skills needed to live indepe
ndently and hold an outsidejob. Moderate to profoundly retarded individuals usually require supervised co
mmunity living.
Family
therapy can help relatives of the mentally retarded develop coping skills. It can also help parents deal wit
hfeelings of guilt or anger. A supportive, warm home environment is essential to help the mentally retarde
d reach their fullpotential.
Prognosis
Individuals with mild to moderate mental retardation are frequently able to achieve some self-
sufficiency and to leadhappy and fulfilling lives. To reach these goals, they need appropriate and consiste
nt educational, community, social,family, and vocational supports. The outlook is less promising for those
with severe to profound retardation. Studies haveshown that these individuals have a shortened life expe
ctancy. The diseases that are usually associated with severeretardation may cause the shorter life span.
People with Down syndrome will develop the brain changes that characterizeAlzheimer's disease in later l
ife and may develop the clinical symptoms of this disease as well.
Prevention
Immunization against diseases such as measles and Hib prevents many of the illnesses that can cause m
entalretardation. In addition, all children should undergo routine developmental screening as part of their
pediatric care.Screening is particularly critical for those children who may be neglected or undernourished
or may live in disease-
producing conditions. Newborn screening and immediate treatment for PKU and hyperthyroidism can usu
ally catch thesedisorders early enough to prevent retardation.
Good prenatal care can also help prevent retardation. Pregnant women should be educated about the ris
ks of drinkingand the need to maintain good nutrition during pregnancy. Tests such as amniocentesis a
nd ultrasonography candetermine whether a fetus is developing normally in the womb.
Resources
Organizations

6. American Association on Mental Retardation (AAMR). 444 North Capitol St., NW, Suite 846, Washington,
D.C. 20001-1512. (800) 424-3688. http://www.aamr.org.
The Arc. 900 Varnum Street NE, Washington, D.C. 20017. (202) 636-2950. http://thearc.org.
Other
Americans With Disabilities Act (ADA) Page. http://www.usdoj.gov/crt/ada/adahom1.htm.
Key terms
Amniocentesis —
A test usually done between 16 and 20 weeks of pregnancy to detect any abnormalities in thedevelopme
nt of the fetus. A small amount of the fluid surrounding the fetus (amniotic fluid) is drawn out through a ne
edleinserted into the mother's womb. Laboratory analysis of this fluid can detect various genetic defects, s
uch as Downsyndrome, or neural tube defects.
Developmental delay —
The failure to meet certain developmental milestones, such as sitting, walking, and talking, atthe average
age. Developmental delay may indicate a problem in development of the central nervous system.
Down syndrome —
A disorder caused by an abnormality at the 21st chromosome. One symptom of Down syndrome ismenta
l retardation.
Extensive support —
Ongoing daily support required to assist an individual in a specific adaptive area, such as dailyhelp with p
reparing meals.
Hib disease —
An infection caused by Haemophilus influenza type b (Hib). This disease mainly affects children underthe
age of five. In that age group, it is the leading cause of bacterial meningitis, pneumonia, joint and bone in
fections,and throat inflammations.
Inborn error of metabolism —
A rare enzyme deficiency; children with inborn errors of metabolism do not have certainenzymes that the
body requires to maintain organ functions. Inborn errors of metabolism can cause brain damage andment
al retardation if left untreated. Phenylketonuria is an inborn error of metabolism.
Limited support —
A predetermined period of assistance required to deal with a specific event, such as training for anew job
.
Phenylketonuria (PKU) —
An inborn error in metabolism that prevents the body from using phenylalanine, an aminoacid necessary
for normal growth and development.
Trisomy —
An abnormality in chromosomal development. Chromosomes are the structures within a cell that carry its
genetic information. They are organized in pairs. Humans have 23 pairs of chromosomes. In a trisomy sy
ndrome, anextra chromosome is present so that the individual has three of a particular chromosome inste
ad of the normal pair. Anextra chromosome 18 (trisomy 18) causes mental retardation.
Ultrasonography — A process that uses the reflection of high-
frequency sound waves to make an image of structuresdeep within the body. Ultrasonography is routinely
used to detect fetal abnormalities.

7. Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
mental
[men´tal]
1. pertaining to the mind.
2. pertaining to the chin.
mental disorder any clinically significant behavioral or psychological syndrome characterized by distressi
ng symptoms,significant impairment of functioning, or significantly increased risk of death, pain, or other d
isability. Mental disorders areassumed to result from some behavioral, psychological, or biological dysfun
ction in the individual. The concept does notinclude deviant behavior, disturbances that are essentially co
nflicts between the individual and society, or expected andculturally sanctioned responses to particular ev
ents.
mental retardation less than average general intellectual functioning that brings with it some degree of i
mpairedadaptation in learning, social adjustment, or maturation, or in all three areas; it is now classified a
s a DEVELOPMENTAL DISABILITY.
Mental retardation is a relative term. Its meaning depends on what society demands of the individual in le
arning, skills,and social responsibility. Many people who are considered developmentally challenged in th
e complex modern worldwould get along normally in a simpler society.
Diagnosis: There is no absolute measurement for retardation. At one time the different types were classifi
ed onlyaccording to the apparent severity of the retardation. Since the most practical standard was intellig
ence, the degree ofretardation was based on the score of the patient on INTELLIGENCE
TESTS such as the INTELLIGENCE
QUOTIENT (IQ). The averageperson is considered to have an IQ of between 90 and 110, and those who sc
ore below 70 are considered mentallyretarded.
In the past, the different groupings were classified in terms such as feebleminded, idiot, imbecile, and mor
on. Today,most health care providers use the following classifications: for IQ's from 50 to 70, mild; 35 to 5
0, moderate; 20 to 35,severe; under 20, profound. Whatever classifications are used, it is agreed that IQ
measurements are only one part ofthe factors to be considered in determining mental retardation. Others,
such as the patient's adaptability to surroundings,the services and training available, and the amount of c
ontrol shown over his or her emotions, are also very important.
About 85 per cent of patients considered mentally retarded are in the least severe, or mild, group. Those i
n this group donot usually have obvious physical defects and thus are not always easy to identify as ment
ally retarded while they arestill infants. Sometimes such a child's mental defects do not show up until the t
ime of entering school, when the childhas difficulty learning and keeping up with others in the same age g
roup. Many persons who are in the mild category, asadults can find employment or a place in society suit
able to their abilities, so that they are no longer identified asmentally retarded.
Cause: The cause of mental retardation is often unidentifiable; known ones are classified as either geneti

8. c or acquired.Genetic conditions include chromosomal abnormalities such as DOWN
SYNDROME and KLINEFELTER'S
SYNDROME and errors ofmetabolism such as PHENYLKETONURIA, HYPOTHYROIDISM, and TAY-SACHS
DISEASE. Acquired conditions may be prenatal, perinatal,or postnatal. Prenatal conditions include RUBELLA
and other viral infections, toxins, placental insufficiency, and blood typeincompatibility. Perinatal causes a
re anoxia, birth injury, and prematurity. Postnatal causes may include infections,poisons, poor nutrition, tr
auma, and sociocultural factors such as deprivation.
Many conditions that can cause severe retardation can be diagnosed during pregnancy, and in some cas
es propertreatment can lessen or even prevent retardation. Proper care for the mother during pregnancy
and for the baby in thefirst months of life is also important.
retardation
[re″tahr-da´shun]
delay; hindrance; delayed development.
mental retardation subnormal general intellectual development, associated with impairment of either lear
ning and socialadjustment, maturation, or both; see also MENTAL RETARDATION.
psychomotor retardation a generalized slowing of physical and emotional reaction, such as that seen in
majorDEPRESSION and in catatonic SCHIZOPHRENIA.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. ©
2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
men·tal re·tar·da·tion
subaverage general intellectual functioning that originates during the developmental period and is associa
ted withimpairment in adaptive behavior. The American Association on Mental Deficiency lists eight medic
al classificationsand five psychological classifications; the latter five replace the three former classification
s of moron, imbecile, andidiot. Mental retardation classification requires assignment of an index for perfor
mance relative to a person's peers ontwo interrelated criteria: measured intelligence (IQ) and overall soci
oadaptive behavior (a judgmental rating of theperson's relative level of performance in school, at work, at
home, and in the community). In general an IQ of 70 orless indicates mental retardation (mild = 50/55-
70; moderate = 35/40-50/55; severe = 20/25-35/40; profound = below20/25); an IQ of 70-
85 signifies borderline intellectual functioning.
Synonym(s): amentia (1) , mental deficiency, oligophrenia
Farlex Partner Medical Dictionary © Farlex 2012
mental retardation
n. Often Offensive
Intellectual disability.

9. The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
mental retardation
a disorder characterized by subaverage general intellectual function with deficits or impairments in the abi
lity to learn andto adapt socially. The cause may be genetic, biological, psychosocial, or traumatic.
Mosby's Medical Dictionary, 9th edition. © 2009, Elsevier.
mental retardation
Neurology Below-
average general intellectual function with associated deficits in adaptivebehavior that occurs before age 1
8; intellectual activity that is significantly below average for a population, and associatedwith impaired soci
al function. Cf Psychological testing.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
men·tal re·tar·da·tion
(men'tăl rē'tahr-dā'shŭn)
Subaverage general intellectual functioning that originates during the developmental period and is associ
ated withimpairment in adaptive behavior. Mental retardation classification requires assignment of an inde
x for performancerelative to a person's peers on two interrelated criteria: measured intelligence (IQ) and o
verall socioadaptive behavior.In general, an IQ of 70 or lower indicates mental retardation. Some clinician
s and laypeople suggest this term may beoffensive in some contexts.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
mental retardation
Intellectual ability so much below average as to preclude the performance of most formsof work or other
social functions. Mentally retarded people usually require supervision and guidance if they are to avoiddis
tress or danger. There are degrees of mental deficiency. So far as INTELLIGENCE
QUOTIENTS (IQs) can be measuredin the mentally retarded, the mildly defective have IQs from 70 down
to about 55; the moderately defective have IQs from54 to 40; and the severely defective have IQs below
40.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
men·tal re·tar·da·tion
(men'tăl rē'tahr-dā'shŭn)
Subaverage general intellectual functioning starting with developmental period, associated with impairme
nt in adaptivebehavior.

10. Medical Dictionary for the Dental Professions © Farlex 2012
mental retardation,
n a disorder characterized by certain limitations in a person's mental functioning and in skills such as com
municating,taking care of him or herself, and social skills. It has many causes, including genetic condition
s such as Downsyndrome, fragile X syndrome, and phenylketonuria (PKU) as well as problems during pre
gnancy or at birth, or due tohealth problems such as diphtheria, measles, or meningitis. It can also be cau
sed by extreme malnutrition, notgetting enough medical care, or being exposed to poisons such as lead o
r mercury.