Mental Retardation
Mental Retardation
Definition
Mental retardation (MR) is a developmental disability that first appears in children under the age of 18. It is defined as a level of intellectual functioning (as measured by standard intelligence tests ) that is well below average and results in significant limitations in daily living skills (adaptive functioning).
Description
Mental retardation begins in childhood or adolescence before the age of 18. In most cases, it persists throughout adult life. A diagnosis of mental retardation is made if an individual has an intellectual functioning level well below average, as well as significant limitations in two or more adaptive skill areas. Intellectual functioning level is defined by standardized tests that measure the
ability to reason in terms of mental age (intelligence quotient or IQ). Mental retardation is generally defined as an IQ score below 70–75. “Adaptive skills” is a term that refers to skills needed for daily life. Such skills include the ability to produce and understand language (communication); home-living skills; use of community resources; health, safety, leisure, self-care, and social skills; self-direction; functional academic skills (reading, writing, and arithmetic); and job-related skills.
In general, children with intellectual and developmental impairments reach such developmental milestones as walking and talking much later than children in the general population. Symptoms of mental retardation may appear at birth or later in childhood. The child’s age at onset depends on the suspected cause of the disability. Some people with mild mental retardation may not be diagnosed before entering preschool or kindergarten. These children typically have difficulties with social, communication, and functional academic skills. Children who have a neurological disorder or illness such as encephalitis or meningitis may suddenly show signs of cognitive impairment and adaptive difficulties.
The level of impairment varies in severity. The Diagnostic and Statistical Manual of Mental Disorders, fourth edition, text revision (DSM-IV-TR), which is the diagnostic standard for mental health care professionals in the United States, classifies four different degrees of mental retardation: mild; moderate; severe; and profound. These categories are based on the person’s level of functioning.
Mild mental retardation
Approximately 85% of people who fall into these categories of mental retardation are in the mildly retarded category. Their IQ scores range from 50 to 70, and they can often learn academic skills up to about the sixth-grade level. They can become fairly self-sufficient and in some cases live independently, with community and social support.
Moderate mental retardation
About 10% of people with mental retardation are considered moderately retarded. People in this category have IQ scores ranging from 35 to 55. They can carry out work and self-care tasks with moderate supervision. They typically acquire communication skills in childhood and are able to live and function successfully within the community in such supervised environments as group homes .
Severe mental retardation
About 3–4% of people with mental retardation are classified as severely retarded. People in this category have IQ scores of 20–40. They may master very basic self-care skills and some communication skills. Many people with this level of impairment can live in a group home.
Profound mental retardation
Only 1–2% of people with mental retardation are classified as profoundly retarded, meaning that they have IQ scores under 20–25. They may be able to develop basic self-care and communication skills with appropriate support and training. Their retardation is often caused by an accompanying neurological disorder. People who are profoundly retarded need high levels of structure and supervision.
The American Association on Intellectual and Developmental Disabilities (AAIDD) (formerly the American Association on Mental Retardation, or AAMR) has developed another widely accepted diagnostic classification system for mental retardation. In this system, mental retardation is defined in terms of environment and context in which the person functions. The AAIDD gives five assumptions that are necessary for defining the presence of mental retardation. A practitioner must consider the limitations of functioning in a community environmental context, including the person’s age group and culture. In addition, cultural and linguistic differences and differences in behavioral, sensory, and other factors should be considered. Strengths should be given consideration along with weaknesses, and the purpose of identifying limitations is to determine what supports the person needs. The final assumption is that when the appropriate supports are available, the quality of life and functional ability of a person with mental retardation will improve. This organization is also systematically pursuing a change in the term “mental retardation,” proposing instead that the more accurate appellation would be “people with intellectual disability.” Members of AAIDD argue for this change based on the stigma associated with the term “mental retardation” or “mentally retarded.”
Demographics
The prevalence of mental retardation in North America is a subject of heated debate. It is thought to be between 1% and 3% depending upon the population, methods of assessment, and criteria of assessment that are used. Many people believe that the actual prevalence is probably closer to 1%, and that the 3% figure is based on misleading mortality rates; cases that are diagnosed in early infancy; and the instability of the diagnosis across the age span. If the 1% figure is accepted, however, it means that about 3 million people with mental retardation live in the United States. The three most common causes of mental retardation, accounting for about 30% of cases, are Down syndrome, fragile X syndrome, and fetal alcohol syndrome . Males are more likely than females to have mental retardation in a 1.5:1 ratio, primarily because of the association with fragile X.
Causes and symptoms
Low IQ scores and limitations in adaptive skills are the hallmarks of mental retardation. Aggression, self-injury, and mood disorders are sometimes associated with the disability. The severity of the symptoms and the age at which they first appear depend on the cause. Children with mental retardation reach developmental milestones significantly later than expected, if at all. If retardation is caused by chromosomal or other genetic disorders, it is often apparent from infancy. If retardation is caused by childhood illnesses or injuries, learning and adaptive skills that were once easy may suddenly become difficult or impossible to master.
In about 40% of cases, the cause of mental retardation cannot be found. The following biological and environmental factors that can cause mental retardation.
Genetic factors
In about 30% of cases of mental retardation, hereditary factors are the cause. Mental retardation may be caused by an inherited genetic abnormality, such as fragile X syndrome. Fragile X—a defect in the X chromosome in which a repeated group of letters in the DNA sequence reaches a certain threshold number that results in impairment—is the most common inherited cause of mental retardation. Single-gene disorders such as phenylketonuria (PKU) and other inborn errors of metabolism may also cause mental retardation if they are not discovered and treated early, although testing of infants for PKU is required at birth and problems associated with this disorder can be avoided through dietary measures. Abnormalities in chromosome number can also be the cause of mental retardation. The presence of an extra chromosome 18 (trisomy 18) or chromosome 21 (trisomy 21 or Down syndrome) will result in some level of mental retardation. In addition, there may be only a partial extra chromosome as a result of accidents at the cellular level, which can result sometimes in milder forms of mental retardation compared to complete trisomies.
Prenatal illnesses and issues
Fetal alcohol syndrome (FAS) affects one in 3,000 children in Western countries. It is caused when mothers drink heavily during the first twelve weeks (trimester) of pregnancy. Some studies have shown that even moderate alcohol use during pregnancy may cause learning disabilities in children. Drug abuse and cigarette smoking during pregnancy have also been linked to mental retardation.
Maternal infections and such illnesses as glandular disorders, rubella, toxoplasmosis, and cytomegalovirus (CMV) infection can result in mental retardation in the child, among many other problems, if the developing fetus is exposed. When the mother has high blood pressure (hypertension) or develops toxemia (also called pregnancy-induced hypertension or preeclampsia) during pregnancy, the flow of oxygen to the fetus may in some cases be reduced, potentially resulting in brain damage and mental retardation.
Birth defects that cause physical deformities of the head, brain, and central nervous system frequently cause mental retardation. A neural tube defect, for example, is a birth defect in which the neural tube that forms the spinal cord does not close completely. This defect, which occurs with varying levels of severity, may cause children to develop an accumulation of cerebrospinal fluid inside the skull (hydroce-phalus). The pressure on the brain resulting from hydrocephalus can lead to changes that cause learning impairment.
Childhood illnesses and injuries
Hyperthyroidism, whooping cough, chicken pox, measles, and Hib disease (a bacterial infection caused by Haemophilus influenzae type B) may cause mental retardation if they are not treated adequately. An infection of the membrane covering the brain (meningitis) or an inflammation of the brain itself (encephalitis) can cause swelling that in turn may cause brain damage and mental retardation. Traumatic brain injury caused by a blow to the head or by violent shaking of the upper body may also cause brain damage and mental retardation in children.
Environmental factors
Neglected infants who are not provided with the mental and physical stimulation required for normal development may suffer irreversible learning impairment. Children who live in poverty and/or suffer from malnutrition, unhealthy living conditions, abuse, and improper or inadequate medical care are at a higher risk. Exposure to lead or mercury can also cause mental retardation. Many children have developed lead poisoning from eating the flaking lead-based paint often found in older buildings.
Diagnosis
If mental retardation is suspected, a comprehensive physical examination and medical history should be done immediately to discover any organic cause of symptoms. Conditions such as hyperthyroidism and PKU are treatable if discovered early enough when the progression of retardation can be stopped and, in some cases, partially reversed. If a neurological cause such as brain injury is suspected, the child may be referred to a neurologist or neuropsychologist for testing.
A complete medical, family, social, and educational history is compiled from existing medical and school records (if applicable) and from interviews with parents. Children are given intelligence tests to measure their learning abilities and intellectual functioning. Such tests include the Stanford-Binet Intelligence Scale , the Wechsler Intelligence Scales, the Wechsler Preschool and Primary Scale of Intelligence, and the Kaufman Assessment Battery for Children. For infants, the Bayley Scales of Infant Development may be used to assess motor, language, and problem-solving skills. Interviews with parents or other caregivers are used to assess the child’s daily living, muscle control, communication, and social skills. The Woodcock-Johnson Scales of Independent Behavior and the Vineland Adaptive Behavior Scales (VABS) are frequently used to evaluate these skills.
Treatment
Federal legislation entitles children with intellectual impairments and developmental disabilities to free testing and appropriate, individualized education and skills training within the school system from ages three to 21. For children under the age of three, many states have established early intervention programs
KEY TERMS
Amniocentesis —A test usually done between 16 and 20 weeks of pregnancy to detect any abnormalities in the development of the fetus. A small amount of the fluid surrounding the fetus (amni-otic fluid) is drawn out through a needle inserted into the mother’s womb. Laboratory analysis of this fluid can detect various genetic defects, such as Down syndrome, or neural tube defects.
Developmental delay —The failure to meet certain developmental milestones, such as sitting, walking, and talking, at the average age. Developmental delay may indicate a problem in development of the central nervous system.
Down syndrome —A genetic disorder characterized by an extra chromosome 21 (trisomy 21), mental retardation, and susceptibility to early-onset Alzheimer’s disease.
Extensive support —Ongoing daily support required to assist individuals in a specific adaptive area, such as daily help with preparing meals.
Hib disease —An infection caused by Haemophilus influenza, type B (Hib). This disease mainly affects children under the age of five. In that age group, it is the leading cause of bacterial meningitis, pneumonia, joint and bone infections, and throat inflammations.
Inborn error of metabolism —A rare enzyme deficiency. Children with inborn errors of metabolism do not have certain enzymes that the body requires to maintain organ functions. Inborn errors of metabolism can cause brain damage and mental retardation if left untreated. Phenylketonuria is an inborn error of metabolism.
Limited support —A predetermined period of assistance required to deal with a specific event, such as training for a new job.
Phenylketonuria (PKU) —An inherited disease in which the body cannot metabolize the amino acid phenylalanine properly. If untreated, phenylketonuria can cause mental retardation.
Trisomy —An abnormality in chromosomal development. Chromosomes are the structures within a cell that carry its genetic information. They are organized in pairs. Humans have 23 pairs of chromosomes. In a trisomy syndrome, an extra chromosome is present so that the individual has three of a particular chromosome instead of the normal pair. An extra chromosome 18 (trisomy 18) causes mental retardation.
Ultrasonography —A process that uses the reflection of high-frequency sound waves to make an image of structures deep within the body. Ultrasonography is routinely used to detect fetal abnormalities.
that assess children, make recommendations, and begin treatment programs. Many day schools are available to help train children with developmental and intellectual impairments in skills such as bathing and feeding themselves. Extracurricular activities and social programs are also important in helping children and adolescents who have developmental and intellectual impairments gain self-esteem.
Training in independent living and job skills is often begun in early adulthood. The level of training depends on the degree of impairment. People with mild levels of functional and intellectual impairment can often learn the skills needed to live independently and hold outside jobs. People with a great level of impairment may require supervised community living in group homes or other residential settings.
Family therapy can help relatives of people with mental retardation develop coping skills. It can also help parents deal with feelings of guilt or anger. A supportive, warm home environment is essential to help people with mental retardation reach their full potential.
Prognosis
People with mild to moderate mental retardation are frequently able to achieve some self-sufficiency and to lead happy and fulfilling lives. To reach these goals, they need appropriate and consistent educational, community, social, family, and vocational supports. The outlook is less promising for those with severe to profound retardation. Studies have shown that these people have a shortened life expectancy. The diseases that are usually associated with severe retardation may cause a shorter life span. People with Down syndrome will develop the brain changes that characterize Alzheimer’s disease in later life and may develop the clinical symptoms of this disease as well.
Prevention
Immunization against diseases such as measles and Hib prevents many of the illnesses that can cause mental retardation. In addition, all children should undergo routine developmental screening as part of their pediatric care. Screening is particularly critical for those children who may be neglected or undernourished or may live in disease-producing conditions. Newborn screening and immediate treatment for PKU and hyperthyroidism can usually catch these disorders early enough to prevent adverse intellectual and developmental effects.
Good prenatal care can also be preventive. Pregnant women should be educated about the risks of alcohol consumption and the need to maintain good nutrition during pregnancy. Tests such as amniocent-esis and ultrasonography can determine whether a fetus is developing normally.
See alsoChildhood disintegrative disorder; Pica.
Resources
BOOKS
American Psychiatric Association. “Mental Retardation.” Diagnostic and Statistical Manual of Mental Disorders, 4th ed., text rev. Washington D.C.: American Psychiatric Press, 2000.
Jaffe, Jerome H., MD. “Mental Retardation.” Comprehensive Textbook of Psychiatry, Benjamin J. Sadock, MD, and Virginia A. Sadock, MD, eds. 7th ed. Philadelphia, PA: Lippincott Williams and Wilkins, 2000.
Julian, John N. “Mental Retardation.” Psychiatry Update and Board Preparation, Thomas A. Stern, MD, and John B. Herman, MD, eds. New York: McGraw Hill, 2000.
PERIODICALS
Bozikas, Vasilis, MD, and others. “Gabapentin for Behavioral Dyscontrol with Mental Retardation.” American Journal Psychiatry (June 2001): 965–66.
Margolese, Howard C., MD, and others. “Olanzapine-Induced Neuroleptic Malignant Syndrome with Mental Retardation.” American Journal Psychiatry (July 1999): 1115A–1116.
ORGANIZATIONS
American Association on Intellectual and Developmental Disabilities (AAIDD) (formerly the American Association on Mental Retardation, or AAMR). 444 North Capitol Street, NW, Washington, DC 20001. Telephone: (800) 424-3688. Web site: http://www.aamr.org
The Arc of the United States (formerly Association of Retarded Citizens of the United States). 1010 Wayne Avenue, Silver Spring, MD 20910. Telephone: (301) 565-3842. Web site: http://thearc.org
National Information Center for Children and Youth and Disabilities. P.O. Box 1492, Washington, DC 20013. Telephone: (800) 695-0285. Web site: http://www.nichcy.org
Paula Anne Ford-Martin, MS
Emily Jane Willingham, PhD