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MENTAL RETARDATION
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below
average level of intellectual functioning, usually defined by an IQ of below
70 to 75, combined with limitations in the skills necessary for daily living.
Daily living skills include such things as communication, the ability to care
for oneself, and the ability to work. The definition of mental retardation
has evolved over the years. Prior categorizations of mental retardation,
defined solely by IQ, have largely been abandoned in favor of an approach
that looks at how much support the retarded person needs in various areas of
his or her life at any given time. Such support can range from intermittent
help in such things as finding housing or a job, to pervasive, daily,
lifelong help in all areas.
Causes
There are
several hundred possible causes of mental retardation. They include genetic
conditions (e.g., Down
syndrome, fragile X syndrome); prenatal problems (e.g., fetal
alcohol syndrome, rubella,
malnutrition); problems apparent at birth (e.g., low birth weight and
prematurity); and problems that occur after birth (e.g., injuries and
childhood diseases like measles that can lead to meningitis and
encephalitis). The most commonly identified causes of mental retardation are
Down syndrome, fragile X syndrome, and fetal alcohol syndrome. In many cases
the cause is never known.
Education
Most
mentally retarded children are capable of learning new things, both in and
out of a formal school setting, but they may learn at a slower pace than
other children. Schools are responsible for providing an appropriate
education for retarded children. Many teachers and parents feel that the
practice of mainstreaming,
or inclusion, which places such children in standard classrooms for at least
part of the day, helps them to feel more a part of society and helps others
to better understand their special needs and capabilities.
Prevention
Many
cases of mental retardation are now prevented by improved health care.
Vaccines against rubella and measles prevent an estimated 3,000 cases of
mental retardation in the United
States yearly. Vaccination against Haemophilus
influenzae b (Hib), a cause of childhood meningitis, is expected to
prevent 3,000 more. Prevention of Rh disease (see Rh
factor), screening and treatment for phenylketonuria,
and emphasis on prenatal care and the dangers of poor nutrition or alcohol
consumption during pregnancy have also resulted in a decrease in cases of
mental retardation in the United States. Mental retardation rates in poor
nations, however, are rising.
History
The
treatment of mentally retarded people has always reflected the changes in
society. They have been officially referred to as idiots and as the
feebleminded. The introduction of the IQ test was followed by a
classification system that used such terms as moron (IQ of 51—70), imbecile
(26—50), and idiot (0—25); later these terms were softened and
classifications redefined somewhat to mild (IQ of 55—70), moderate (40—54),
severe (25—39), and profound (0—24) retardation. The term mentally
retarded itself, although still commonly used, has been replaced in some
settings by the term developmentally disabled.
Mentally
retarded people have been subjected to unnecessary institutionalization and,
as a result of the eugenics
movement, involuntary sterilization. The deinstitutionalization movement of
the 1970s reflected a concern for the civil rights of mentally retarded. Very
few of the mentally retarded are now institutionalized; most now live
independently, with their families, or in group homes. The emphasis on
education and self-sufficiency seen in the late 20th cent. mirrors a similar
movement in the 1840s.
Bibliography
See M.
Adams, Mental Retardation and Its Social Dimensions (1971); A. Clarke
et al., ed., Mental Retardation: The Changing Outlook (1985); E.
Zigler, Understanding Mental Retardation (1986); American Association
on Mental Retardation, Mental Retardation: Definition, Classification, and
Systems of Support (1992).
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LEVELS OF MENTAL
RETARDATION
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This group constitutes by far the largest number of those
labeled mentally retarded. Persons in this group are considered
"educable", and their intellectual levels as adults are comparable
to that of the average 8 to 11 year old child. Their social adjustment often
approximates that of the adolescent, although they tend to lack the normal
adolescent's imagination, inventiveness, and judgement. Ordinarily they do
not show the signs of brain pathology or other physical anomalies. Often they
require some measure of supervision due to limited ability to foresee the
consequences of their actions. With early diagnosis, parental assistance, and
special educational programs, the great majority can adjust socially, master
simple academic and occupational skills, and become self-supporting citizens.
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Individuals in this group are likely to fall in the
educational category of "trainable". In adult life, individuals
classified as moderately retarded attain intellectual levels similar to that
of the average 4 to 7-year-old child. While some of the brighter ones can be
taught to read and write a little, and some manage to achieve a fair command
of spoken language, the rate of learning is relatively slow among members of
this group, and the level of conceptualizing extremely limited. Physically,
they usually appear clumsy and ungainly, and they suffer from bodily
deformities and poor motor coordination. A distinct minority of these
children is hostile and aggressive, but typically they present an affable and
somewhat vacuous personality picture.
With early diagnosis, parental help, and adequate opportunities for
training, most of the moderately retarded can achieve partial independence in
daily self-care, acceptable behavior, and economic usefulness in a family or
other sheltered environment. Whether or not they require institutionalization
usually depends on their general level of adaptive behavior and the nature of
their home situation.back to top |
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Individuals in this group are sometimes referred to as
"dependent retarded". Among these individuals, motor and speech
development is severely retarded and sensory defects and motor handicaps are
common. These mental retardates can develop limited levels of personal
hygiene and self-help skills, which somewhat lessen their dependence, but all
their lives they will be dependent on others for care. However, many profit
to some extent from training and can perform simple occupational tasks under
supervision.
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The term "life
support" mental retardate is sometimes used in referring to individuals
in this category. Most of these persons are severely deficient in adaptive
behavior and unable to master any but simplest tasks. Useful speech, if
develops at all, is on the rudimentary level. Severe physical deformities,
central nervous system pathology, and retarded growth are typical, and
convulsive seizures, mutism, deafness, and other physical anomalies are
common. These retardates must maintain in custodial care all their lives.
However, health and resistance to disease is lowered, and a short life
expectancy is usual.
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TYPES OF MENTAL
RETARDATION
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The different Types of mental retardness are : |
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Down's Syndrome (Mongolism) |
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The term mongolism has been used in referring to this
syndrome because persons so afflicted frequently have almond-shaped slanting
eyes. A number of physical features are often found among children with
Down’s syndrome, but very few of these children have all of the
characteristics commonly thought of as typifying this group. In addition to
slanting eyes, the skin of the eyelids tends to be abnormally thick; the face
and nose are often flat and broad, as is the back of the head; and the
tongue, which seems too large for the mouth, may show deep fissures. The iris
of the eye is frequently speckled. The neck is often short and broad, as are
the hands, which tend to have creases across the palms. The fingers are
stubby and the little finger is often more noticeable curved than the other
fingers.
Mongoloids are particularly susceptible to circulatory, gastrointestinal,
and respiratory disorders. However, antibiotics, better medical care, and a
more healthful and stimulating environment are increasing the life expectancy
of many of the victims of this disorder.Research has shown that possible chromosomal anomalies lead to this disorder. Subsequent studies have shown that 95 percent of people with Down’s syndrome have 47 chromosomes instead of the normal component of 46 resulting from a trisomy of chromosome 21. (Normally chromosomes have no extra arm, but in this condition there is a presence of an extra arm on chromosome 21.) The reason of trisomy of chromosome 21 is not clear, but the anomaly would appear to result from defective genes leading to some malfunction in the mechanics of the growth process. Trisomy of chromosome 21 is influenced by metabolic factors, but it is also possible that the older the mother, the greater the probability of exposure to radiation that may result in gene mutation. There is no known effective treatment. When parents have had a child with Down’s syndrome, they are usually quite concerned about having further children. In such cases genetic counseling may provide some indication of the risk – which may be quite small – of abnormality in additional children. back to top |
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Phenylketonuria is a rare metabolic disorder. In PKU the
baby appears normal at birth but lacks an enzyme needed to break down
phenylalanine, an amino acid found in protein foods. When this condition is
undetected, the phenylalanine builds up in the blood and leads to brain
damage. The disorder usually becomes apparent between 6 and 12 months after
birth, although such symptoms as vomiting, a peculiar odor, infantile eczema,
(a skin disorder in infants), and seizures (fits) may become apparent during
the early weeks of life. Often the first symptoms noticed are signs of mental
retardation, which may be moderate to severe, depending on the degree to
which the disease has progressed. Motor incoordination and other neurological
manifestations relating to the severity of brain damage are also common, and
often the eyes, skin, and hair of untreated PKU patients are very pale.
PKU is thought to result from metabolic alterations involving recessive
genes, and 1 person in 70 is thought to be a carrier. Methods for the early detection of PKU have been developed, and dietary and related treatment procedures are utilized. With early detection and treatment – preferably before an infant is 6 months old– the deterioration process can be arrested so that levels of intellectual functioning may range from borderline to normal functioning. However, a few children suffer mental retardation despite restricted phenylalanine intake and other treatment measures. For a baby to inherit PKU, both parents must carry the recessive gene. Thus when one child in a family has PKU, it is important that other children in such families be screened as well. back to top |
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Cretinism provides a dramatic illustration of mental
retardation resulting from endocrine imbalance. In this condition, the
thyroid either has failed to develop properly or has undergone degeneration
or injury. In either case, the infant suffers from a deficiency in thyroid
secretion. Brain damage resulting from this insufficiency is most marked
during the prenatal and early postnatal periods of rapid growth.
Although most cases of cretinism result from lack of iodine in the diet,
thyroid deficiency may also occur as the result of birth injuries (involving
bleeding into the thyroid) or in connection with infectious diseases such as
measles, whooping cough, or diphtheria. The resulting clinical picture will
depend on the age at which the thyroid deficiency occurs, as well as on the
degree and duration of the deficiency.Typical descriptions of cretins involve cases in which there has been a severe thyroid deficiency from an early age, often even before birth. Such a cretin has a dwarflike, thick-set body and short, stubby extremities. His height is usually just a little over 3 feet, the shortness accentuated by slightly bent legs and a curvature of the spine. He walks with a shuffling gait that is easily recognizable. His head is large, with abundant black, wiry hair; his eyelids are thick, giving him a sleepy appearance; his skin is dry and thickened and cold on the touch. Other pronounced physical symptoms include a broad, flat nose, large and flappy ears, a protruding abdomen, and failure to mature sexually. The cretins reveal a bland personality, and his thought processes tend to be sluggish. Most cretins fall within the moderate and severe categories of mental retardation, depending on the extent of brain damage. In cases with less pronounced physical signs of cretinism, the degree of mental retardation is usually less severe. Early treatment of cretinism with thyroid gland extract is considered essential, and infants not treated until after first year of life may have permanently impaired intelligence. In long–standing cases, thyroid treatment may have some ameliorating effects, but the damage to the individual’s nervous system and general physical development is beyond repair. back to top |
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Mental retardation is associated with a number of
conditions in which there are relatively gross alterations in head size and
shape, and where the causal factors have not been definitely established.
In macrocephaly ("large headedness"), for example there
is an increase in the size and weight of the brain, an enlargement of the
skull, and visual impairment, convulsions, and other neurological symptoms
resulting from the supporting structure for brain tissue. Other cranial
anomalies include microcephaly
and hydrocephalus.
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The term microcephaly means "small
headedness". It refers to a type of mental retardation resulting from
impaired development of the brain and a consequent failure of the cranium to
attain normal size. The most obvious characteristics of microcephalic is his
small head, the circumference of which rarely exceeds 17 inches, as compared
with normal of approximately 22 inches. Microcephalics differ considerably
from each other in appearance, although there is a tendency for the skull to
be coned shaped, with a receding chin and forehead. Microcephalics fall
within the moderate,
severe,
and profound
categories of mental retardation, but the majority shows little language
development and is extremely limited in mental capacity.
Microcephaly may result from a wide range of factors that impair brain
development, including intrauterine infections and pelvic irradiation of the
mother during the early months of pregnancy. A number of cases of
microcephaly that occurred in Hiroshima and Nagasaki apparently
resulted from atomic bomb explosions during World War II. The role of genetic
factors is not clear yet. The treatment is ineffective once faulty
development has occurred, and, at present, preventive measures focus on the
avoidance of infection and radiation during pregnancy.back to top |
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Hydrocephalus is a relatively rare condition in which the
accumulation of an abnormal amount of cerebrospinal fluid within the cranium
causes damage to the brain tissues and enlargement of the cranium.
In congenital cases of hydrocephalus, the head is either already enlarged
at birth or begins to enlarge soon thereafter, presumably as a result of a
disturbance in the formation, absorption, or circulation of the cerebrospinal
fluid. The disorder can also develop in infancy or early childhood following
the development of a brain tumor, subdural hemetoma,(clot in the brain
covering), meningitis,(infection of brain covering) or other such conditions.
Here the condition appears to result from a blockage of the cerebrospinal
pathways and an accumulation of fluid in certain brain areas.The clinical picture of hydrocephalus depends on the extent of neural damage, which, in turn, depends on the age at onset and the duration and severity of disorder. In chronic cases the chief symptom is the gradual enlargement of the upper part of the head out of all proportion to the face and the rest of the body. While the expansion of the skull helps minimize destructive pressure on the brain, serious brain damage occurs nonetheless, leading to intellectual impairment and such other effects as convulsions and impairment or loss of sight and hearing. The degree of intellectual impairment varies, being severe or profound in advanced cases. A good deal of attention has been directed to the surgical treatment of hydrocephalus, and with early diagnosis and treatment this condition can usually be arrested before severe brain damage has occurred. |
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CAUSES FOR MENTAL
RETARDATION
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Mental Retardation Associated With Sociocultural Deprivation |
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Adverse sociocultural conditions, particularly those
involving a deprivation of normal stimulation, may play a primary role in the
etiology of mental retardation.
Two subtype of mental retardation can be mental retardation associated with extreme sensory and social deprivation, such as prolonged isolation during the development years and cultural-familial retardation, in which the child is not subjected to extreme isolation but rather suffers from an inferior quality of interaction with his cultural environment and with other people. back to top |
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Children who fall in this category are usually mild mental
retardates; they make up the majority of persons labeled as mentally retarded
and show no identifiable brain pathology. They are usually not diagnosed as
mentally retarded until they enter school and have serious difficulties in
their studies.
A number of studies point out that most of these children come from
poverty-stricken, unstable, and often disrupted family backgrounds
characterized by a lack of intellectual stimulation, an inferior quality of
interaction with others, and general environmental deprivation.Since a child’s current level of intellectual functioning is based largely on previous learning - and since schoolwork requires complex skills such as being able to control one's attention, follow instructions, and recognize the meaning of a considerable range of words - the child is at a disadvantage from the beginning if his environment has deprived him of the opportunity to learn requisite background skills and be motivated toward further learning. Thus with each succeeding year these children tend to fall farther behind in school performance and relative ratings on intelligence tests, unless remedial measures are undertaken. Many of these children do reveal a history of prematurity, inadequate diets, a little or no medical care. back to top |
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Mental retardation tends to run in families. This is
particularly of mild
retardation, which presumably is heavily influenced by the many
genetic factors responsible for variations in intelligence. Genetic factors
play a much clearer role in the etiology of relatively rare types of mental
retardation such as Down's
Syndrome. Here, specific genetic defects are responsible for
metabolic alterations that adversely affect development of the brain. Genetic
defects leading to metabolic alterations may, of course, involve many other
developmental anomalies besides mental retardation. In general, mental
retardation associated with known genetic-chromosomal defects is moderate to
severe in degree.
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Mental retardation may be associated with a wide range of
conditions due to infection. The fetus of a mother with certain virus
diseases, such as German Measles, may suffer brain damage, as may the fetus
of a mother with Syphilis. And, as in the case of viral encephalitis, brain damage
may result from infections occurring after birth.
A number of toxic agents, such as carbon monoxide and lead, may also cause
brain damage during fetal development or after birth. In some instances,
immunological agents, such as antitetanus serum or typhoid vaccine, may lead
to brain damage. Similarly certain drugs taken by the mother during pregnancy
may lead to congenital malformations, or an overdose of drugs administered to
the infant may result in toxicity and brain damage. In rare cases, brain damage
results from incompatibility in blood types between mother and fetus – Rh or
ABO system incompatibility. Fortunately, early diagnosis and blood
transfusions can now minimize the effects of this disorder.back to top |
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Follow up studies of children born prematurely (weighing
less than 1500 grams at birth) have revealed a high incidence of neurological
disorders, including mental retardation. In fact, very small premature babies
are about ten times more likely to be mentally retarded than normal infants.
Physical injury at birth can also result in retardation. Although normally
the fetus is well protected by its fluid filled bag, and its skull appears
designed to resist delivery stresses, accidents do happen during delivery, as
well as after birth.Difficulties in labor due to malposition of the fetus or other complications may irreparably damage the infant’s brain. Bleeding within the brain is probably the most common result of birth trauma. Anoxia – lack of sufficient oxygen to the brain stemming from delayed breathing or other causes – is another type of birth trauma that may damage the brain. back to top |
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In recent years a good deal of scientific attention has
been focused on the damaging effects of ionizing radiation on sex cells and
other bodily cells and tissues. Radiation may act directly on the fertilized
ovum or may produce gene mutations in the sex cells of either or both
parents, which, in turn, may lead to defective offspring.
Sources of harmful radiation were once limited primarily to high-energy X
rays used for diagnosis and therapy, but the list has grown to include
nuclear weapons testing and other radioactive materials to which people may
be exposed. back to top |
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Deficiencies in proteins and other essential nutrients
during early development can result in irreversible physical and mental
damage. Protein deficiencies in the mother’s diet, as well as in the baby’s
diet after the birth, have been pinpointed as particularly potent causes of
lowered intelligence.
A limited number of cases of mental retardation are also associated with
other biological agents, such as brain tumors that either damage the brain
tissue directly or lead to increased cranial pressure and concomitant brain
damage. In some instances of mental retardation – particularly of severe
and profound
types – the causes are uncertain or unknown, although extensive brain
pathology is evident. |
It has been seen that significant changes in adaptive
capacity are possible through special education and other rehabilitative
measures. The degree of changes that can be expected is related, of course, to
the individual and his level of mental retardation.
Fortunately, most mental retardates do not need to be institutionalized.
Mild retardates need classes, which usually emphasize reading and other basic
school subjects, budgeting and money matters, and the development of
occupational skills have been notably successful, and have helped many mild
retardates become independent, productive members of the community. Classes for
the moderately and severely retarded usually have more limited objectives, but
they emphasize development of self-care and other skills that will enable
retardates to function adequately and be of assistance in either a family or
institutional setting. Simple job skills can also be learned by these
retardates. Training is built on step by step progression. Target areas of improvement are mapped out, such as improvement in personal grooming, social behavior, basic academic skills, and simple occupational skills. Within each area, specific skills are divided into simple components that can be learned and reinforced before more complex behaviors are required. Target areas are not selected arbitrarily, but realistically reflect the requirements of mentally retardate's life situation.
One problem that inflicts great anxiety on parents is whether or not to institutionalize their mentally retarded child. In general, the ones who are institutionalized fall into two groups:
a) those who, in infancy and childhood, manifest severe mental retardation and associated physical impairment, and who enter the institution at an early age, and
b) those who, in adolescence, usually have no physical impairments but show mild mental retardation and fail to adjust socially,
eventually requiring institutionalization for delinquent or other acting-out behavior.
The families of those in the first group come from all socioeconomic levels, whereas a significantly higher percentage of families of those in the second group come from lower educational and occupational strata.
Institutionalization is not recommended where the child makes a satisfactory adjustment at home and in any special class or training school that he may attend during the day. The effect of institutionalization on a mentally retarded youth depends heavily on the institution's facilities and on the youth himself.
The problem of preventing mental retardation involves the question of genetic factors as well as a wide range of biochemical, neurophysiological, and sociocultural conditions.
The frontiers in this field of prevention are:
1 . Work in genetics has revealed the role of genetic defects in faulty development and tests that have been devised to identify parents who have these faulty genes, thus making it possible to provide them with genetic counseling.
2. The alleviation of sociocultural conditions, that deprive children of the necessary stimulation, motivation and opportunity for normal learning and development.
The government has taken initiative in this direction to provide adequate medical and general health care for mother and baby- prior to and during pregnancy, and after birth of the baby- particularly for the socially disadvantaged.
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TREATMENTS, OUTCOMES AND
PREVENTION
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It has been seen that significant changes in adaptive
capacity are possible through special education and other rehabilitative
measures. The degree of changes that can be expected is related, of course,
to the individual and his level of mental retardation.
Fortunately, most mental retardates do not need to be institutionalized.
Mild retardates need classes, which usually emphasize reading and other basic
school subjects, budgeting and money matters, and the development of
occupational skills have been notably successful, and have helped many mild
retardates become independent, productive members of the community. Classes
for the moderately and severely retarded usually have more limited
objectives, but they emphasize development of self-care and other skills that
will enable retardates to function adequately and be of assistance in either
a family or institutional setting. Simple job skills can also be learned by
these retardates. Training is built on step by step progression. Target areas of improvement are mapped out, such as improvement in personal grooming, social behavior, basic academic skills, and simple occupational skills. Within each area, specific skills are divided into simple components that can be learned and reinforced before more complex behaviors are required. Target areas are not selected arbitrarily, but realistically reflect the requirements of mentally retardate's life situation. One problem that inflicts great anxiety on parents is whether or not to institutionalize their mentally retarded child. In general, the ones who are institutionalized fall into two groups: a) those who, in infancy and childhood, manifest severe mental retardation and associated physical impairment, and who enter the institution at an early age, and b) those who, in adolescence, usually have no physical impairments but show mild mental retardation and fail to adjust socially, eventually requiring institutionalization for delinquent or other acting-out behavior. The families of those in the first group come from all socioeconomic levels, whereas a significantly higher percentage of families of those in the second group come from lower educational and occupational strata. Institutionalization is not recommended where the child makes a satisfactory adjustment at home and in any special class or training school that he may attend during the day. The effect of institutionalization on a mentally retarded youth depends heavily on the institution's facilities and on the youth himself. The problem of preventing mental retardation involves the question of genetic factors as well as a wide range of biochemical, neurophysiological, and sociocultural conditions. The frontiers in this field of prevention are: 1 . Work in genetics has revealed the role of genetic defects in faulty development and tests that have been devised to identify parents who have these faulty genes, thus making it possible to provide them with genetic counseling. 2. The alleviation of sociocultural conditions, that deprive children of the necessary stimulation, motivation and opportunity for normal learning and development. The government has taken initiative in this direction to provide adequate medical and general health care for mother and baby- prior to and during pregnancy, and after birth of the baby- particularly for the socially disadvantaged. |
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