sections include: a new understanding of mental retardation, mechanisms and factors, diagnosis and treatment
The term “mental retardation” covers a wide range of conditions. People with these conditions have an equally wide range of functioning: some live independently, others live in structured environments, and still others need constant care. It is impossible to discuss all these conditions here in detail, but we can describe what they have in common.
There are two definitions of mental retardation. The most commonly used, from the American Psychiatric Association, requires:
- intellectual functioning significantly below average—an IQ of approximately 70 or below on an individually administered test
- problems in meeting standards the person’s cultural group expects for his or her age (referred to as deficits or impairments in adaptive functioning) in at least two of these areas: communication, self-care, home living, social/ interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety
- onset of these problems before the person turns 18
The American Association on Mental Retardation (AAMR) also focuses on adaptive functioning but differs in how it defines significantly low intellectual function. Because of the variability of IQ measurement, the AAMR endorses a more inclusive definition, with IQ extending as high as 75. This may seem like a small difference, but because those scores fall on the steeply rising slope of a bell curve, the shift doubles the number of people with mental retardation.
Mental retardation affects a person’s ability to reason. It limits an individual’s ability to think from the concrete to the abstract, from the specific to the general case. In everyday life, mental retardation affects judgment, socialization, education, and work. More severe cases of mental retardation may affect a person’s safety, ability to perform everyday activities, and communication.
Sometimes a family knows that a child is mentally retarded when he or she is born, perhaps even before. Using amniocentesis and chorionic villi sampling, we can now detect Down’s syndrome, which involves an easily recognized chromosomal abnormality, while a child is still in the mother’s womb. Babies born with this condition also have recognizable physical traits, including eyelid and palm folds. However, people with Down’s syndrome (and other forms of mental retardation) have a wide range of intelligence and abilities, not to mention diverse personalities. Thus, a family cannot know how their baby will learn and behave until he or she actually starts to grow up.
Other forms of mental retardation are not as obvious at first. Usually parents become aware of their child’s slow acquisition of skills when comparing him or her with other children of the same age. Most toddlers with mental retardation are relatively slow in acquiring language. They may or may not have behavioral difficulties. Delays in gross motor abilities, such as difficulty in crawling or walking, may be associated with mental retardation, but in the absence of other delays, they usually point to other brain impairments, such as neuromuscular and metabolic disorders. Variances among very young children may not be obvious, but they become more apparent as time passes—especially to parents—and are evident by age 2 or 3. Families usually consult their pediatricians when they decide the delay is significant.
A family can also learn that a child is mentally retarded when doctors evaluate him or her for other brain dysfunctions. For example, parents may bring an infant to a pediatrician because he or she is having seizures, and the doctor might diagnose tuberous sclerosis, with accompanying mental retardation.
Other cases of mental retardation result from brain disorders that are obvious and dramatic. For instance, a child may have a bad case of meningitis, which interferes with the brain’s development. Brain trauma at an early age can also slow a child’s mental development permanently.
In most cases, we do not know why people are bornA New Understanding of Mental Retardation with mental retardation. Despite this, parents often feel guilty when they learn about their child’s condition. They fear that they are responsible. Frequently families focus on insignificant events that they think might have been the cause, such as a cold during pregnancy, one glass of wine, or the choice to use low forceps. Such worries are unfounded.
A New Understanding of Mental Retardation
Over the years our understanding of mental retardation has grown in several important ways. First, we have identified many biomedical conditions associated with it. For instance, we know that a pregnant woman drinking significant amounts of alcohol creates a greater chance that her child will be born with fetal alcohol syndrome. The past two decades have also seen an explosion in our knowledge of genetics and metabolism. Whole new classes of metabolic disease have been identified that are associated with mental retardation. Most are rare, but some are treatable, with the result that some mental retardation can be prevented. Newer genetic techniques allow us to determine causes of mental retardation that were unknown five years ago. The completion of the sequencing of the human genome holds promise for tremendous growth in determining the causes of mental retardation.
Second, by better understanding the natural history of mental retardation, we have found ways to lower the risk that children will be born with or develop the condition. To decrease the number of cases of fetal alcohol syndrome, public health initiatives warn pregnant women about the risks of drinking. Statewide screening programs routinely test all newborns for phenylketonuria (PKU) and many other metabolic disorders for which early treatment may prevent mental retardation. Government initiatives such as removing the lead from gasoline have decreased mental retardation caused by lead poisoning. Seat belt laws and accident prevention campaigns have lowered the frequency of trauma. Immunization programs have greatly decreased the rate of measles, Hemophilus influenzae, and rubella, consequently reducing the cases of mental retardation due to encephalitis, meningitis and congenital infection.
We expect similar results from programs designed to lower the rate of teenage pregnancy, maternal smoking, and alcohol use, all of which raise a child’s risk of being born with mental retardation. Intensive prenatal care of “high risk” mothers attempts to lower rates of premature birth, which is another risk factor. Intensive care of newborn infants and such programs as WIC, Medicaid, EPSDT, and CHIP improve access to health care. All women who might become pregnant are also urged to take folic acid supplements, which reduces the risk of spina bifida.
Our third area of progress has been in recognizing that people with mental retardation can be integrated effectively into the larger society and be valuable, productive family members and citizens. The intellectual limitation may not prove handicapping. Individuals with mental retardation have increasingly been accepted as functioning members of society—many live in community settings, are competitively employed, and are accepted for their abilities. This may be the most important change in the field.
Education has reemerged as the dominant discipline in the care of children with mental retardation. Education is directed toward maximizing function in community settings. The growth of community programs has helped families maintain their children at home and allowed adults to participate in society.
We have also come to understand that mental retardation may not be a lifelong disorder. Children’s IQs can change as they mature. Some seem to plateau, with their IQs declining in later childhood. Children with Down’s syndrome sometimes follow this pattern; they continue to learn, but lag farther behind their peers. But other individuals who are diagnosed with mental retardation during their school years develop sufficient adaptive behavior abilities that they no longer fit the diagnosis as adults. In fact, very young children may show intellectual functioning significantly below average but improve so much that they are not considered mentally retarded by the time they start school. This has led some authorities to defer diagnosing mental retardation until a child is 3 years old, and raises the possibility of altering the severity of people’s conditions through early intervention.
Mechanisms and Factors
There are approximately 7 million Americans with some form of mental retardation. About 2 million of these children and adults need ongoing services and supports. At least 5 million more people will be identified as having mental retardation at some point in their lives.
It is clear that mental retardation can result from many causes. We see so many different types of cognitive dysfunction in mental retardation that it is unlikely they all stem from a single mechanism in the brain’s development. For example, people with Down’s syndrome have a relative weakness in language abilities compared with their visual-spatial abilities, while those with Williams syndrome have the opposite pattern. Furthermore, because most forms of mental retardation affect cognition while sparing other brain functions, they probably do not result from a broad-ranging mechanism.
Studies of brain structure have revealed that most people who have mental retardation have normal-looking brains. Investigations of brain chemistry have not yielded a testable hypothesis. That means the primary area of research into the mechanism of mental retardation remains focused on how people learn. Researchers have studied brain plasticity, memory, attention, language, and perception, learning useful things about particular conditions but leaving much more to discover.
Overall, mental retardation is more common in boys than in girls, which may point to susceptibility genes on the X chromosome. Girls have two X chromosomes, so they can compensate for an abnormal gene on one, but boys have only one copy. Even more than chromosomal abnormalities and single-gene disorders, mental retardation seems to cluster in families. However, the condition can arise in many ways.
Diagnosis and Treatment
Assessing the cognitive development of infants and young children requires considerable experience. Mental retardation may mimic such conditions as a language disorder, attention deficit/ hyperactivity disorder, deafness, schizophrenia and autism, or a child with mental retardation may have any of those conditions as well. Mental retardation may also be a component of neurodegenerative diseases.
Pediatricians are usually the first professionals to detect mental retardation. Psychologists diagnose it by administering a standardized measure of intellect (for example, Bayley, WPPSI, WISC, or WAIS) and a standardized measure of adaptive behavior. The tests must be individually administered and be appropriate to the person’s language. Psychologists may supplement their test findings by asking parents or teachers about the child.
Early diagnosis gives families more time to adjust to their children’s needs and abilities. It enables early intervention, heads off behavioral and emotional disturbances, and allows long-term planning. Diagnosis allows families to enter a system of services that, at their best, provide coordinated, continuous, and individualized care. Support groups help parents better understand their child’s disorder; provide practical information on management, entitlements, and rights; and serve as a resource to identify professionals who “do a good job.” Our primary way of helping children with mental retardation is special education.
At present, there is no medical treatment for mental retardation. Most people with the condition have the same health needs as the rest of us. However, they have a higher than average risk of such neurological problems as seizures and cerebral palsy; behavior/emotional disorders such as autism, depression, anxiety and adjustment disorders; and impairments in vision and hearing. Medical treatment or therapy is available for these associated impairments.
Some forms of mental retardation are associated with medical conditions that require special care. People with Down’s syndrome have an above-average risk of thyroid, heart, blood, orthopedic, and gastrointestinal disorders. There are neurodevelopmental pediatricians, geneticists, neurologists, and psychiatrists who specialize in caring for individuals with mental retardation.
The prognosis for people with mental retardation depends on the severity of their condition, any associated impairments, and the extent to which their community can help them maximize their abilities.
In the future, noninvasive functional neuroimaging technology holds promise that we will better understand the nature of mental retardation. Even more promising is analysis of how various genes express themselves, made possible by the human genome project. We also anticipate the new pharmacological and behavioral interventions will help people with mental retardation improve their abilities and adaptive functioning.
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