What
is mental retardation?
According to the new definition by the American Association on Mental Retardation (AAMR),
an individual is considered to have mental retardation based on the following three
criteria: intellectual functioning level (IQ) is below 70-75; significant limitations
exist in two or more adaptive skill areas; and the condition is present from childhood
(defined as age 18 or less) (AAMR, 1992).
What are the adaptive skills essential for daily
functioning?
Adaptive skill areas are those daily living skills needed to live, work and play in the
community. The new definition includes ten adaptive skills: communication, self-care, home
living, social skills, leisure, health and safety, self-direction, functional academics,
community use and work.
Adaptive skills are assessed in the person's typical environment across all aspects of an
individual's life. A person with limits in intellectual functioning who does not have
limits in adaptive skill areas may not be diagnosed as having mental retardation.
How many people are affected by mental retardation?
Various studies have been conducted in local communities to determine the prevalence of
mental retardation. The Arc reviewed many of these prevalence studies in the early 1980s
and concluded that 2.5 to 3 percent of the general population has mental retardation (The
Arc, 1982). A recent review of prevalence studies generally confirms this distribution
(Fryers, 1993).
Based on the 1990 census, an estimated 6.2 to 7.5 million people have mental retardation.
Mental retardation is 12 times more common than cerebral palsy and 30 times more prevalent
than neural tube defects such as spina bifida. It affects 100 times as many people as
total blindness (Batshaw & Perret, 1992).
Mental retardation cuts across the lines of racial, ethnic, educational, social and
economic backgrounds. It can occur in any family. One out of ten American families is
directly affected by mental retardation.
How does mental retardation affect individuals?
The effects of mental retardation vary considerably among people, just as the range of
abilities varies considerably among people who do not have mental retardation. About 87
percent will be mildly affected and will be only a little slower than average in learning
new information and skills. As children, their mental retardation is not readily apparent
and may not be identified until they enter school. As adults, many will be able to lead
independent lives in the community and will no longer be viewed as having mental
retardation.
The remaining 13 percent of people with mental retardation, those with IQs under 50, will
have serious limitations in functioning. However, with early intervention, a functional
education and appropriate supports as an adult, all can lead satisfying lives in the
community.
AAMR's new definition no longer labels individuals according to the categories of mild,
moderate, severe and profound mental retardation based on IQ level. Instead, it looks at
the intensity and pattern of changing supports needed by an individual over a lifetime.
How is mental retardation diagnosed?
The AAMR process for diagnosing and classifying a person as having mental retardation
contains three steps and describes the system of supports a person needs to overcome
limits in adaptive skills.
The first step in diagnosis is to have a qualified person give one or more standardized
intelligence tests and a standardized adaptive skills test, on an individual basis.
The second step is to describe the person's strengths and weaknesses across four
dimensions. The four dimensions are:
1. Intellectual and adaptive behavior skills
2. Psychological/emotional considerations
3. Physical/health/etiological considerations
4. Environmental considerations
Strengths and weaknesses may be determined by formal testing, observations, interviewing
key people in the individual's life, interviewing the individual, interacting with the
person in his or her daily life or a combination of these approaches.
The third step requires an interdisciplinary team to determine needed supports across the
four dimensions. Each support identified is assigned one of four levels of intensity -
intermittent, limited, extensive, pervasive.
Intermittent support refers to support on an "as needed basis." An
example would be support that is needed in order for a person to find a new job in the
event of a job loss. Intermittent support may be needed occasionally by an individual over
the lifespan, but not on a continuous daily basis.
Limited support may occur over a limited time span such as during transition from
school to work or in time-limited job training. This type of support has a limit on the
time that is needed to provide appropriate support for an individual.
Extensive support in a life area is assistance that an individual needs on a daily
basis that is not limited by time. This may involve support in the home and/or support in
work. Intermittent, limited and extensive supports may not be needed in all life areas for
an individual.
Pervasive support refers to constant support across environments and life areas and
may include life-sustaining measures. A person requiring pervasive support will need
assistance on a daily basis across all life areas.
What does the term "mental age" mean when
used to describe the person's functioning?
The term mental age is used in intelligence testing. It means that the individual received
the same number of correct responses on a standardized IQ test as the average person of
that age in the sample population.
Saying that an older person with mental retardation is like a person of a younger age or
has the "mind" or "understanding " of a younger person is incorrect
usage of the term. The mental age only refers to the intelligence test score. It does not
describe the level and nature of the person's experience and functioning in aspects of
community life.
What are the causes of mental retardation?
Mental retardation can be caused by any condition which impairs development of the brain
before birth, during birth or in the childhood years. Several hundred causes have been
discovered, but in about one-third of the people affected, the cause remains unknown. The
three major known causes of mental retardation are Down syndrome, fetal alcohol syndrome
and fragile X.
The causes can be categorized as follows:
- Genetic conditions - These result from abnormal-ity of genes inherited from parents,
errors when genes combine, or from other disorders of the genes caused during pregnancy by
infections, overexposure to x-rays and other factors. Inborn errors of metabo-lism which
may produce mental retardation, such as PKU (phenylketonuria), fall in this category.
Chromosomal abnormalities have likewise been related to some forms of mental retardation,
such as Down syndrome and fragile X syndrome.
- Problems during pregnancy - Use of alcohol or drugs by the pregnant mother can cause
mental retardation. Malnutrition, rubella, glandular disor-ders and diabetes,
cytomegalovirus, and many other illnesses of the mother during pregnancy may result in a
child being born with mental retardation. Physi-cal malformations of the brain and HIV
infection originating in prenatal life may also result in mental retardation.
- Problems at birth -Although any birth condition of unusual stress may injure the
infant's brain, prematurity and low birth weight predict serious problems more often than
any other conditions.
- Problems after birth - Childhood diseases such as whooping cough, chicken pox, measles,
and Hib disease which may lead to meningitis and encephali-tis can damage the brain, as
can accidents such as a blow to the head or near drowning. Substances such as lead and
mercury can cause irreparable damage to the brain and nervous system.
- Poverty and cultural deprivation - Children in poor families may become mentally
retarded because of malnutrition, disease-producing conditions, inad-equate medical care
and environmental health. hazards. Also, children in disadvantaged areas ma be deprived of
many common cultural and day-to-day experiences provided to other youngsters. Research
suggests that such under-stimulation can result in irreversible damage and can serve as a
cause of mental retardation.
Can mental retardation be prevented?
During the past 30 years, significant advances in research have prevented many cases of
mental retardation. For example, every year in the United States, we prevent:
- 250 cases of mental retardation due to phenylketonuria (PKU) by newborn screening and
dietary treatment;
- 1,000 cases of mental retardation due to congenital hypothyroidism thanks to newborn
screening and thyroid hormone replacement therapy,
- 2,000 cases of mental retardation or deafness by use of Rhogam to prevent Rh disease and
severe jaundice in newborn infants;
- 3,000 cases of mental retardation due to measles encephalitis thanks to measles vaccine;
and untold numbers of cases of mental retardation caused by rubella during pregnancy
thanks to rubella vaccine (Alexander, 1991).
In addition, with the new vaccine against Hib disease, 3,000 to 4,000 cases of mental
retardation can now be prevented.
New attempts at treatment of a variety of causes are being developed. There are now
unproved ways to manage head trauma, asphyxia (lack of oxygen) and infectious diseases to
reduce their adverse effects on the brain. Early intervention programs with high-risk
infants and children have shown remarkable results in reducing the predicted incidence of
subnormal intellectual functioning.
Finally, early comprehensive prenatal care and preventive measures prior to and during
pregnancy increase a woman's chances of preventing mental retardation.
References
- AAMR (1992). Mental Retardation: Definition. Classification, and Systems of Supports
9th Edition.
- Alexander, D. (1991). Keynote Address. In President's Committee on Mental Retardation, Summit
on the National Effort to Prevent Mental Retardation and Related Disabilities.
- Batshaw, M. and Perret, Y. (1992). Children With Disabilities: A Medical Primer.
Baltimore: Paul H. Brookes Publishing Co.
- Fryers, T. (1993). Epidemiological Thinking in Mental Retardation: Issues in Taxonomy
and Population Frequency. In Bray, N.W., International Review of Research in Mental
Retardation, Vol. 19. Novato, Calif: Academic Therapy Publications.
- The Arc (1982). The Prevalence of Mental Retardation (out-of-print).
Where can I go for more information?
For more information about the new definition and classification system for mental
retardation, call AAMR at 1-800-424-3688 for phone numbers of the authors who are
available to answer specific questions.
Staff at the national headquarters of The Arc can also help you with a variety of other
topics related to mental retardation.
Or, call your local chapter of The Arc.
