Mental Retardation

Mental retardation is a condition marked by significantly lower intelligence than the average for individuals of the same age and by delays in developing social skills, communication skills, and the ability to care for oneself and live independently.


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Adaptive behaviors

Amercans vwth Disabilities Act

Cognitive disabilities

Developmental disabillties

Individuals with Disabilities Education Act (IDEA)


What Is Mental Retardation?

The definition of mental retardation changes as researchers study its causes and develop new ways of understanding its effects. Current definitions focus on intelligence levels and on the skills and behaviors for everyday living that people develop as they grow.


An intelligence quotient (IQ) is a test score that doctors and schools use to measure thinking, learning, and problem-solving skills. The IQ score for an average person always is set at 100. People who score above 120 are considered gifted. People who score below 80 are considered to have mental retardation. IQ scores define the severity of mental retardation using the following ranges:

  • IQ 70-79: borderline
  • IQ 55-69: mild
  • IQ 40-54: moderate
  • IQ 25-39: severe
  • IQ below 25: profound.

A mentally retarded person is likely to be limited in most or all kinds of intelligence. The lower a person's IQ score, the more impaired his or her learning capacity is apt to be.

Adaptive behaviors

People with mental retardation are more limited than the average person in how well and how quickly they can learn to function in their environment. Limitations often involve language and communication, social skills, self-care, health and safety skills, leisure skills, the ability to live at home and/or in the community, and the ability to perform up to average standards in school or at work. This does not mean all people with mental retardation are unable to take care of themselves, however. Those with borderline mental retardation often are able to lead independent lives as adults if they receive extra support while they catch up to their peers in learning adaptive behaviors.

Mental illness

Mental retardation is not a mental illness. Sometimes people with mental retardation also have depression, anxiety, or other mental illnesses, just as people with average intelligence do. Oftentimes, though, they lead happy and healthy lives.

What Causes Mental Retardation?

Mental retardation sometimes has a genetic cause, resulting from one or more chromosomal abnormalities. Other times, though, mental retardation may be the result of problems during pregnancy that affect development of the fetal brain and central nervous system. Babies may be born with mental retardation if their mothers do not receive proper nutrition and medical care during pregnancy, if their mothers have infections during pregnancy or childbirth, or if their mothers are exposed to alcohol, drugs, or environmental toxins during pregnancy. Many different causes of mental retardation have been identified, but often a specific cause cannot be pinpointed for a specific individual.

Did You Know?

  • About 1 percent of the U.S. population has mental retardation.
  • About 85 percent of those people fall into the mild to moderate range, which means that with the proper support they can learn to lead independent lives as adults.
  • The other 15 percent fall into the severe to profound range, which means they are likely to need support with activities of daily living for most of their lives.
  • Mental retardation affects people of all ethnic, social, and economic backgrounds.

Chromosomal abnormalities

Chromosomes are the threadlike structures in body cells that carry genetic information. Most cells in the human body have 23 pairs of chromosomes. Chromosome pair 23 determines whether a person is female (two X chromosomes) or male (one X chromosome and one Y chromosome) as well as other traits. Chromosomes 1 through 22 determine all our other traits and characteristics. Mental retardation may occur when a baby has an extra chromosome, an abnormal or partially missing chromosome, or a mislocated chromosome. The chromosomal abnormalities most often linked to mental retardation are Down syndrome and Fragile X.

Down syndrome

Down syndrome results from an abnormality on chromosome 21. People with Down syndrome may have three copies of this chromosome throughout the body (trisomy 21), or they may have three copies in some but not all cells (mosaic trisomy 21), or some of the genetic material from chromosome 21 may have become attached to a different chromosome (translocation trisomy 21). The physical differences that may result from chromosome 21 errors include mild to moderate mental retardation, a flat facial profile, an upward slant to the eyes, a short neck, a single deep crease on the palm, and increased risk of hearing loss, vision problems, thyroid disorders, and heart disease. Chromosome 21 errors have been linked to a mother's age. The incidence of Down syndrome in the children of mothers older than age 45 is 1 in 20, while for children of mothers younger than age 30 the incidence is less than 1 in 1,000.

Fragile X

Fragile X results from an abnormality on the X chromosome. It affects girls (XX) about twice as often as boys (XY), but symptoms are more severe in boys, because boys do not have a second X chromosome to help counter the effects of the defective one. The physical differences caused by Fragile X may include severe mental retardation, autism, a large head, protruding ears, a prominent jaw, and large testicles.

Definitions Change

Just 100 years ago, people with mental retardation were identified as "eternal children," "mentally deficient," "mental defectives," "imbeciles," and the "feeble-minded." Even doctors used those terms, publishing medical texts with titles such as Mental Defectives: Their History, Treatment and Training (1904), Mentally Deficient Children: Their Treatment and Training (1900), and "On the Permanent Care of the Feeble Minded," published in The Lancet medical journal (1903).

Fortunately, times have changed and so have attitudes toward people with mental retardation. We now know that many people with retardation can live meaningful, fulfilling lives, as long as they are in the right environment and get the extra support they need.

Metabolic disorders

Sometimes called "inborn errors of metabolism," these conditions result from abnormalities in the genes that govern how the body produces and handles amino acids, proteins, enzymes, hormones, and nutrients. One metabolic disorder that can cause mental retardation is phenylketonuria (FEN-il-KEE-toe-NOOR-ee-a), which is linked to a lack of the enzyme needed to process the amino acid phenylalanine (FEN-ill-AL-a-neen). Other such disorders include hypothyroidism (HY-poe-THY-royd-iz-um), linked to an underdeveloped, underactive, or damaged thyroid gland, which is needed to produce hormones essential for normal growth and brain development. Many metabolic disorders can be detected at birth by a blood test and treated through special diets, medications, and hormone therapy. If treatment is started early enough, mental retardation often can be prevented.

Brain development disorders

Problems that interfere with fetal development of the brain, spinal cord, and central nervous system may result in mental retardation, making proper prenatal medical care and good nutrition essential for pregnant women. Factors that are linked to brain development disorders include the mother's intake of folic acid (a B vitamin) and her exposure to teratogens (toxins), such as environmental waste, alcohol, tobacco, street drugs, and even some prescription medications. Brain development disorders include anencephaly * , hydrocephalus * , spina bifida * , autism, and fetal alcohol syndrome. Many people with either spina bifida or autism have brain development disorders but are not mentally retarded.

Fetal alcohol syndrome

When a pregnant woman drinks alcohol or takes drugs (legal or illegal), these substances are transmitted directly to the fetus. Mental retardation that is linked to a mother's drinking is known as fetal alcohol syndrome (FAS). In addition to mental retardation, children with FAS may have attention disorders, learning disabilities, skeletal problems, and distinctive facial characteristics, including widely spaced eyes, a shortened or flattened nose, and abnormalities in the shape and placement of the ears.


Serious infections can harm a baby's developing brain before birth or during early life. Viral infections linked to mental retardation include cytomegalovirus (SIE-toe-MEG-a-lo-VY-rus) and the rubella virus, which causes German measles. Encephalitis (en-SEF-uh-LIE-tis) and meningitis (MEN-in-JY-tis), two infections that involve inflammation of the brain, also can cause mental retardation.

* anencephaly (AN-en-SEF-uh-lee) is a condition present at birth in which most of the brain is missing.

* hydrocephalus (HY-droe-SEF-uh-lus) is a condition, sometimes present at birth, in which there is an abnormal buildup of fluid within the skull, leading to enlargement of the skull and pressure on the brain.

* spina bifida (SPY-nuh BIF-ih-duh) is a condition present at birth in which the spinal column is imperfectly closed, leaving part of the spinal cord exposed and often leading to neurological and other problems.

Other causes

Other possible causes of mental retardation include premature or difficult birth, severe head injury, and lead poisoning. In many cases, however, doctors cannot identify specific causes, particularly when the mental retardation is mild. Because mental skills and intelligence are defined statistically by their distribution along a normal (bell) curve and by their variance from an average defined as 100, there always will be some individuals who are classified as intellectually gifted (IQ above 120) and others who are classified as mentally retarded (IQ below 80).

Diagnosing Mental Retardation

Chromosomal abnormalities and metabolic disorders often are diagnosed by doctors during prenatal testing or at birth. In other cases, however, a parent, caregiver, or teacher may be the first to notice that a baby or young child is not demonstrating new skills at the same pace as his or her peers. For example, the child may not crawl, walk, or talk by the expected age.

Using thorough physical and psychological examinations, doctors try to rule out other possible causes of the child's delays, such as hearing or vision problems, neuromuscular disorders, emotional or behavioral problems, learning or speech disorders, abuse, or a troubled home life. Pediatricians use blood tests, brain scans, genetic testing, and other medical tests to look for underlying physical disorders. Psychologists use developmental tests to help determine whether babies and children actually are behind peers, and they use standardized intelligence tests to compare the abilities of school-aged children to those of average children in the same age group. Psychologists also may observe the child at play, in school, and interacting with family members before making a diagnosis of mental retardation. Because developmental delays are not always linked to mental retardation, and because they may improve with physical treatment or changes in the child's environment, psychologists often schedule repeated evaluations over time to measure delays and assess improvements in intelligence and adaptive behaviors.

Living with Mental Retardation


Parents who learn that an infant or child has mental retardation often are shocked, and they may be overwhelmed by feelings of sadness, helplessness, or anger until they adjust to the news. Family counselors and support groups often are needed to help parents learn how to meet the special needs of mentally retarded children and balance those needs with other family responsibilities, particularly to siblings who also must adjust to the situation. To help children with mental retardation, many families work with a team of specialists that includes psychologists, speech and language pathologists, physical and occupational therapists, social workers, and special education teachers.

IDEA 1990

In 1975, the U.S. Congress passed Public Law 94-142, the Education for All Handicapped Children Act, which was renamed the Individuals with Disabilities Education Act (IDEA) in 1990. IDEA guaranteed all children with disabilities a "free appropriate public education." It said that children with disabilities should be educated alongside their nondisabled peers "to the maximum extent appropriate," a practice known as "mainstreaming." Since then, teachers, principals, parents, civil rights advocates, and even courts of law have debated whether or not students with mental retardation should be educated in the same classrooms as their nondisabled peers. Some argue that this practice places too great a burden on teachers.

In general, current policy favors including students with mental retardation in regular classrooms to whatever extent is possible. Under IDEA, every disabled child has the right to an annual, written individualized education plan (IEP) starting at age 3. Teachers, therapists, and parents work together to develop the best plan for educating the child, which may mean full inclusion in regular classes, partial inclusion supplemented by special education classes, or separate classes full-time. IDEA also ensures that children with special needs get free access to any education-related services they need, including transportation, counseling, and special therapy.


Children with mental retardation face many emotional challenges. They may know that they are "different" from their peers in ways that they may not understand. They may think that their families consider them a burden or an annoyance or a reason for shame, and they may be aware that they are "special needs" students in school. However, children with mental retardation can benefit from treatment and support in learning academic skills and the adaptive behaviors needed for everyday living. They also may get a boost in self-esteem by realizing that they, like other children, are unique and valuable individuals.


Adults with severe or profound mental retardation requiring constant supervision often enter nursing homes or other residential facilities that offer intensive 24-hour care. However, the majority of adults with mild to moderate mental retardation can achieve varying degrees of independence. Because they may want or need some support and guidance, many continue to live with family members or in group homes, apartment clusters, or hostels designed especially for people with special needs. Some are able to hold jobs and participate in community events such as the Special Olympics, which can help them develop greater self-esteem. Others are able to get married and start their own families.

Special Olympics
and Best Buddies

Since John Fitzgerald Kennedy became president in 1960, his family often has been in the spotlight. Some members of the Kennedy family have chosen to use their celebrity status to improve the quality of life for people with mental retardation, to honor JFK's sister Rosemary Kennedy, who was born with severe mental retardation in 1918.

Eunice Kennedy Shriver founded the Special Olympics in 1968, when she organized the First International Special Olympics Games in Chicago, Illinois. Since then, the Special Olympics has expanded into an international program of year-round sports training and athletic competition for more than 1 million children and adults with mental retardation. The program is designed to help participants develop physical fitness and motor skills, self-esteem, and a sense of community. In the United States alone, about 25,000 communities now have Special Olympics programs, and 150 countries worldwide also have accredited programs.

Just over a decade ago, Eunice Shriver's son Anthony started his own program to help the mentally retarded. Best Buddies is a mentoring program that pairs people with mental retardation with high school and college students in the community. More than 500 campuses in the United States, Canada, Greece, and Egypt now have a Best Buddies program.

To learn more about these organizations, visit their websites at and .



Burke, Chris, and Jo Beth McDaniel. A Special Kind of Hero: Chris Burke's Own Story. New York: Doubleday, 1991. This book tells the life story of Chris Burke, a young actor with Down syndrome who starred in the television show Life Goes On.

Levitz, Mitchell, and Jason Kingsley. Count Us In: Growing Up with Down Syndrome. New York: Harcourt, 1993. Two young men with Down syndrome write about their experiences growing up with the condition and share their viewpoints about education, employment, ambitions, families, and marriage.


American Association on Mental Retardation, 444 North Capitol Street Northwest, Suite 846, Washington, DC 20001-1512. Founded in 1876, this is the oldest and largest multidisciplinary organization of professionals and others concerned with mental retardation and related disabilities.
Telephone 800-424-3688

The Arc of the United States, 1010 Wayne Avenue, Suite 650, Silver Spring, MD, 20910. This is a national organization for people with mental retardation and related developmental disabilities. Its publications include It's My Future!: Planning for What I Want in My Life, a spiral-bound planning guide for adults with cognitive and developmental disabilities, and Different Moms, a video about parents with developmental disabilities.
Telephone 301-565-3842

U.S. National Information Center for Children and Youth with Disabilities, P.O. Box 1492, Washington, DC 20013. This national clear-inghouse offers fact sheets, publications, resources, and referrals in English and Spanish for families and teachers.
Telephone 800-695-0285 (voice/TTY)

See also
Attention Deficit Hyperactivity Disorder
Birth Defects and Brain Development
Fetal Alcohol Syndrome
Genetics and Behavior
Learning Disabilities
Testing and Evaluation

Also read article about Mental Retardation from Wikipedia

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