Mental Retardation is
a disorder in which a
person’s overall intellectual functioning is well below average, with an
intelligence quotient (IQ) around 70 or less. Individuals with mental
retardation also have a significantly impaired ability to cope with
common life
demands and lack some daily living skills expected of people in their
age group
and culture. The impairment may interfere with learning, communication,
self-care, independent living, social interaction, play, work, and
safety.
Mental retardation appears in childhood, before age 18.
About 1 percent of the
general population has
mental retardation, although some estimates range as high as 3 percent.
Mental
retardation is slightly more common in males than in females. It occurs
in
people of all racial, ethnic, education, and economic backgrounds.
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II
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DEGREES OF
SEVERITY
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Mental health clinicians
have defined four degrees of
severity of mental retardation based on IQ score. These are mild
retardation
(IQ range 50-55 to about 70), moderate (IQ range 35-40 to 50-55), severe
(IQ
range 20-25 to 35-40), and profound (IQ level below 20-25). People of
average
intelligence score from about 90 to 110 on IQ tests. See also Intelligence;
Psychological
Testing: Intelligence Tests.
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Mild
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Mildly affected individuals
comprise about 85 percent of
people with retardation. They often cannot be distinguished from normal
children until they attend school. Although they learn more slowly,
people with
mild retardation usually can develop academic skills equivalent to the
sixth-grade level. As adults, they can work and live in the community if
helped
when they experience unusual social or economic stress. Some may marry
and have
children.
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B
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Moderate
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About 10 percent of people
with mental retardation
are moderately retarded. They can progress to about the second-grade
level in
academic skills. By adolescence, they usually have good self-care
skills—such
as eating, dressing, and going to the bathroom—and can perform simple
tasks. As
adults, most can work at unskilled or semiskilled jobs with supervision.
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Severe
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Severe retardation affects
3 to 4 percent of mentally
retarded individuals. Severely retarded individuals may learn to talk
during
childhood and develop basic self-care skills. In adulthood they can
perform
simple tasks with close supervision. They often live in group homes or
with
their families.
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Profound
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About 1 to 2 percent of
retarded people
have profound mental retardation and require constant care. Profoundly
retarded
individuals can understand some language, but they have little ability
to talk.
They often have a neurological condition that accounts for their
retardation.
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CAUSES
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Scientists can identify
a specific cause in 60 to
70 percent of mental retardation cases. Causes include genetic
conditions,
disorders that occur as a fetus develops during pregnancy, and problems
during
or after birth. Some cases of mental retardation have multiple causes.
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A
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Genetic Causes
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Genetic causes include
single-gene defects such as
Fragile X syndrome and chromosomal disorders such as Down syndrome.
Scientists
in 1992 identified Fragile X syndrome as the most common inherited cause
of
mental retardation, responsible for up to 10 percent of cases. People
with this
condition inherit a defective gene that results in a weak spot on the X
chromosome, a sex chromosome. The weak part of the chromosome is
susceptible to
breaking. Fragile X syndrome is more likely to cause retardation in
males then
females.
Chromosomal disorders,
which occur in about 7 out of every
1000 infants, involve an abnormal number of chromosomes or changes in
the
structure of a chromosome. Down syndrome occurs when people inherit all
or part
of an extra copy of a pair of chromosomes known together as chromosome
21.
Although regarded as genetic disorders, chromosomal disorders are not
necessarily inherited. Both parents may have normal genes, with the
defect resulting
from a random error when chromosomes reproduce.
Other genetic causes of
mental retardation are
inborn errors of metabolism. They involve inheritance of a defective
gene
unable to produce enzymes or proteins needed for critical cell
functions.
Scientists have identified more than 300 gene disorders involving inborn
errors
of metabolism. Many can result in mental retardation, including
phenylketonuria
(PKU), Tay-Sachs disease, galactosemia, homocystinuria, maple syrup
urine
disease, and biotinidase deficiency.
Another common cause of
mental retardation,
congenital hypothyroidism, occurs in about 1 in every 4000 births.
Infants with
this disorder are unable to produce enough thyroxine, a hormone secreted
by the
thyroid gland. Mental retardation and stunted growth result unless they
receive
thyroid replacement therapy.
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External Causes
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A variety of problems
during a woman’s pregnancy
can cause mental retardation in her child. These problems include
malnutrition;
a mother’s use of alcohol or drugs; environmental toxins such as lead
and
mercury; viral infections, including rubella (see German Measles)
and
cytomegalovirus; and untreated diseases such as diabetes mellitus. Fetal
alcohol syndrome results from excessive consumption of alcohol during
pregnancy
and is the most common preventable cause of mental retardation in the
United
States. It occurs in 1 to 3 out of every 1000 births. Malnutrition
during
pregnancy is a common cause of mental retardation in developing
countries,
where many women do not consume adequate amounts of protein and other
necessary
nutrients.
Some cases of mental retardation
result from
problems during birth, including premature birth, very low birth weight,
and
stresses to the fetus such as deprivation of oxygen. Infectious diseases
during
childhood, which are easily preventable through immunization, also can
cause
mental retardation when they result in complications. For example,
measles,
chicken pox, and whooping cough may lead to encephalitis and meningitis,
which
can damage the brain.
Physical trauma to the
brain can also cause mental
retardation. Brain damage may result from accidental blows to the head,
near
drowning, severe child abuse, and childhood exposure to such toxins as
lead and
mercury. Experts believe that poverty and a lack of stimulation during
infancy
and early childhood can be factors in mental retardation. Children
raised in
poor environments are more likely to experience malnutrition, lack of
routine
medical care, and environmental health hazards.
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PREVENTION
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Newborn screening programs
can prevent some cases of
mental retardation by identifying inherited conditions that may lead to
retardation.
All states in the United States require a blood test for congenital
hypothyroidism and phenylketonuria (PKU). Infants with PKU cannot
metabolize
the amino acid phenylalanine, found in foods that contain protein. Once
identified, these infants can be given a low-phenylalanine diet that
prevents
retardation. Some states require newborn screening for additional
inherited
diseases.
Adult screening tests
can identify carriers of other
conditions before couples conceive a child. Individuals and couples with
a
family history of mental retardation can seek genetic counseling to
evaluate
their own risks and need for screening. Specialized laboratory tests,
including
amniocentesis, can detect Down syndrome and other genetic disorders in
the
early stages of pregnancy.
Proper prenatal care,
avoidance of alcohol and drugs
during pregnancy, and routine immunization against measles and other
childhood
diseases can prevent some forms of retardation. With pregnant women at
risk of
bearing a baby with a very low birth weight, magnesium sulfate
treatments can
reduce the risk of mental retardation in the infant by 70 percent.
New ways of preventing
mental retardation may
emerge as the Human Genome Project identifies more disease-causing
genes. This
research may lead to new screening tests and gene therapies that can
remove
defective genes that cause mental retardation and replace them with
normal
genes.
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TREATMENT AND
CARE
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Treatment and care of
mentally retarded people has
changed greatly in modern times. Until the 1800s, families kept children
with
retardation at home, hidden from public view. Later, state governments
built
large institutions to house the retarded, and physicians advised parents
to
institutionalize retarded children. Few retarded children had the
opportunity
for education and training. Experts now recognize that mental
retardation is
not always a lifelong disorder. Some individuals diagnosed with mild
mental
retardation as children may gradually develop new skills through early
intervention and educational services. As adults, they may function in
everyday
life at a level that no longer warrants a diagnosis of retardation.
All but the most profoundly
retarded people
usually can best develop their full potential by living in the
community. Most
people with mental retardation have the capacity to learn, advance
intellectually, develop job and social skills, and become full
participants in
society. They may marry, have families, and be indistinguishable from
other
people. In order to achieve their potential, mentally retarded children
need
special education and training, which ideally begins in infancy and
continues
until they establish an adult role.
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Education
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Early intervention programs
can provide specialized
teaching and other services for infants, toddlers, and preschool
children. Such
programs try to optimize development of the individual’s strengths.
Whenever
possible, children with mental retardation attend the same school they
would
attend if they did not have mental retardation. But they receive
instruction
modified for their specific needs. Federal law in the United States
requires
that every school district provide services to mentally retarded
children in
regular schools. See Education of Students with Mental
Retardation.
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Living
Arrangements
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The number of mentally
retarded people living in
large, state-sponsored institutions has declined since the 1960s and
many of
these institutions have closed. Most mentally retarded people live in
one of a
variety of community settings: group homes, supervised homes, adult
foster
care, personal care homes, board-and-care homes, and other settings.
Group homes provide care,
supervision, and training
for a small number of unrelated individuals. In supervised apartments or
homes,
individuals live alone or with roommates. Trained staff live in a
separate unit
in the same location. In adult foster care, a mentally retarded person
lives
with a family other than his or her own family. The foster family
provides
meals, a comfortable home environment, and assistance with daily living
skills.
Staff in a personal care home can provide help with dressing, bathing,
and
other personal needs. Board-and-care homes provide sleeping rooms and
meals.
Some social-service agencies provide assistance for people with
retardation to
live in the same kind of rented or owned apartments or houses as other
people
in the community. Profoundly retarded people may live in nursing homes
that
provide daily nursing care.
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Employment
Opportunities
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Many people with mental
retardation are capable of
working in a variety of full- or part-time jobs. Studies have shown that
most
employers are satisfied with the performance, work attendance, and
loyalty of
people with mental retardation. Employees with retardation do not have
more
accidents on the job than other workers, nor do they raise employee
health
insurance or benefit costs. Because people with retardation may take
longer to
master job tasks, supervisors may spend additional time with them during
the
first few days or weeks of employment. Job coaching programs established
in
some communities provide a specialist who helps in the initial training
of a
mentally retarded individual. Employers who hire individuals with mental
retardation may be eligible for government tax credits and other
incentives.
People with more severe mental retardation may work in other settings,
including special facilities known as sheltered workshops.
Despite their ability
to work, most people with mental
retardation do not have jobs. Surveys indicate that only about 36
percent of
mentally retarded adults have full-time or part-time jobs. Reasons for
this low
employment rate may include a lack of training in vocational and social
skills,
lack of encouragement from others, and a scarcity of community programs
that
aid people with mental retardation in finding and maintaining
employment. In
addition, employers may hesitate to hire people with mental retardation
because
of uncertainty over how to provide accommodations for their disability.
