Mental retardation is a condition in which people have below average intelligence that limits their ability to function normally. The condition, which is present from birth or childhood, has many different causes. Its effects range from mild to profound.
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Fetal alcohol syndrome
Fragile x syndrome
What Is Mental Retardation?
Mental retardation is a condition in which people have significantly below average mental functioning (an intelligence quotient or IQ of 70-75 or less compared to the normal average of 100), causing problems with everyday
Studies in the 1980s suggest that between 2.5 and 3 percent of all people in the United States are considered mentally retarded. According to the 1990 census, 6.3 and 7.5 million people in the United States have mental retardation.
The condition, which is more common in boys than girls, begins at birth or in childhood. If a person with normal intelligence becomes impaired as an adult, such as in severe mental illness or brain injury, the condition is not called mental retardation.
How Is Mental Retardatiofi Classified?
There are four levels of mental retardation: mild, moderate, severe, and profound. These levels are determined by performance on standardized IQ tests and by the potential to learn adaptive skills such as communication and social interaction.
The vast majority of people with mental retardation have IQ levels of 55 to 69 and are considered mildly retarded. Mildly retarded children often go undiagnosed until they are well into their school years. They are often slower to walk, talk, and feed themselves than most other children. They can learn practical skills, including reading and math, up to about the fourth to sixth grade level. Mildly retarded adults usually build social and job skills and can live on their own.
A much smaller number of people with mental retardation have IQs ranging from 40 to 54 and are considered moderately retarded. Children who are moderately retarded show noticeable delays in developing speech and motor skills. Although they are unlikely to acquire useful academic skills, they can learn basic communication, some health and safety habits, and other simple skills. They cannot learn to read or do math. Moderately retarded adults usually cannot live alone, but they can do some simple tasks and travel alone in familiar places.
An even smaller percentage of people with mental retardation have IQs ranging from 20 to 39 and are considered severely mentally retarded. Their condition is likely to be diagnosed at birth or soon after. By preschool age, they show delays in motor development and little or no ability to communicate. With training, they may learn some self-help skills, such as how to feed and bathe themselves. They usually learn to walk and gain a basic understanding of speech as they get older. Adults who are severely mentally retarded may be able to follow daily routines and perform simple tasks, but they need to be directed and live in a protected environment.
Only a very few people with mental retardation have IQs of 0 to 24 and are considered severely mentally retarded. Their condition is usually diagnosed at birth, and they may have other medical problems and need nursing care. Children who are profoundly retarded need to be continuously supervised. These children show delays in all aspects of development. With training, they may learn to use their legs, hands, and jaws. Adults who are profoundly retarded usually learn some speech and may learn to walk. They cannot take care of themselves and need complete support in daily living.
What Causes Mental Retardation?
Mental retardation is a complex condition, which may be caused by the interaction of many factors. In about 75 percent of cases, the exact cause is never known. Causes of mental retardation include defects in the genes * or chromosomes * , injuries or conditions that develop while a fetus * is developing in the womb, diseases of early childhood, and environmental influences. The three major causes of mental retardation are Down syndrome, fetal alcohol syndrome, and fragile X.
The role of genetics
If one or both parents have mental retardation, there is a much greater chance that their children will also have this condition. There are many genetic (inherited) causes of mental retardation that arise from defects or omissions in the genetic material passed from parent to child.
Sometimes mental retardation is caused by an abnormality in the chromosomes rather than the individual genes. Down syndrome, one of the most common causes of mental retardation, is caused by an extra chromosome in the cells. Another fairly common chromosomal defect called fragile X syndrome causes mental retardation mainly in boys.
* genes are chemicals in the body that help determine a person's characteristics, such as hair or eye color, and are inherited from a person's parents. They are located on chromosomes found in the cells of the body.
* chromosomes (KRO-mo-somes) are threadlike structure inside the nucleus of cells on which the genes are located.
* A fetus (FEE-tus) in humans, is the developing offspring from nine weeks after conception until birth.
* toxoplasmosis (tok-so-plaz-MO-sis) is a disease caused by a single-celled organism sometimes found in the stool of cats.
Problems during pregnancy
Infections in pregnant women such as German measles (rubella) or toxoplasmosis * also are a cause of mental retardation. Even though the mother may not be harmed by the infection,
Pregnant women who drink too much alcohol risk having a mentally retarded child through a condition known as fetal alcohol syndrome (FAS). This is a common, and preventable, cause of mental retardation. Some drugs (for example, cocaine or amphetamines), when taken during pregnancy, may harm the mental development of the unborn child. Maternal malnutrition and exposure to radiation during pregnancy can also cause mental retardation.
Problems during childbirth
Babies born prematurely (born before the normal duration of pregnancy has ended) are more likely to be mentally retarded than babies born at full term, especially if the baby is very premature and weighs less than 3.3 pounds (1.5 kg). Problems during childbirth such as an interruption in the supply of oxygen to the baby during the delivery can also cause mental retardation.
Disorders occurring after birth
Mental retardation can also be caused by problems after birth such as lead or mercury poisoning, severe malnutrition, accidents that cause severe head injuries, an interruption in the supply of oxygen to the brain (for example, near-drowning), or diseases such as encephalitis, meningitis, and untreated hypothyroidism in infants. Some of these conditions are more likely to occur in children raised in circumstances of severe poverty, neglect, or abuse.
Living with Mental Retardation
There is no cure for mental retardation. Treatment focuses on helping people who have the condition develop to their full potential by building their educational, behavioral, and self-help skills. For children with mental retardation, the support of parents, specially trained educators, and the community helps them reach to their fullest ability. Parents may benefit from ongoing counseling to discuss their options and to help them cope with the changes in their household that arise from living with someone who has mental retardation.
Many children with mental retardation benefit from living at home or in a community residence and going to a regular school. Schools in all states are now required to provide appropriate education for children with mental retardation until they are 21 years old.
Can Mental Retardation Be Prevented?
There is no certain way to prevent mental retardation. Improved health care, prenatal testing, and public health education are making it possible to avoid some cases of mental retardation. People who want to become parents can get genetic counseling to determine the likelihood of mental retardation from an inherited disorder. Medical tests such as amniocentesis * , chorionic villus sampling * , and ultrasonography * can help detect inherited metabolic and chromosomal disorders linked to mental retardation. Vaccinations can prevent pregnant women from getting infections such as German measles that can harm developing fetuses. Preventing toxo-plasmois and avoiding drugs and alcohol during pregnancy also help prevent mental retardation. Screening blood tests for newborns can detect some disorders at birth, allowing for earlier treatment. It is also important to protect babies from lead poisoning and head injuries.
* amniocentesis (am-nee-o-sen-TEE-sis) is a test in which a long, thin needle is inserted in the mother's uterus to obtain a sample of the amniotic fluid from the sac that surrounds the fetus. The fetal cells in the fluid are then examined for genetic defects.
* chorionic villus sampling (KOR-ee-on-ik VIL-lus sampling) is a test in which a small tube is inserted through the cervix and a small piece of the placenta supporting the fetus is removed for genetic testing.
* ultrasonography (ul-tra-so-NOG-ra-fee) is a painless test that uses high-frequency sound waves to record and show the shape of the fetus in the mother's uterus.
Fetal Alcohol Syndrome
Sudden Infant Death Syndrome
Kaufman, Sandra Z. Retarded Isn't Stupid, Mom! Baltimore: Brooks Publishing Co., 1988.
Shyer, Marlene. Welcome Home, Jellybean. New York: Macmillan, 1988.
ARC of the United States (formerly known as the Association for Retarded
Citizens), 500 East Border Street, Arlington, TX 76010. This
organization provides information, advocacy, and local resources for
people with mental retardation.
U.S. National Institute of Child Health and Human Development (NICHD),
31 Center Drive, Building 31, Room 2A32, Bethesda, MD 20892-2425. NICHD
is one of the National Institutes of Health. Its Mental Retardation and
Developmental Disabilities Branch (MRDD) supports 15 regional Mental
Retardation Research Centers and posts useful fact sheets at its