Mental retardation is a developmental disability that first appears in children under the age of 18 and, in most cases, persists throughout adulthood. A person is considered mentally retarded if he or she has an intellectual functioning level well below average and significant limitations in two or more adaptive skill areas. Intellectual functioning level is defined by standardizedtests that measure the ability to reason in terms of mental age (intelligencequotient or IQ). Mental retardation is defined as IQ score below 70-75. Adaptive skills are the skills needed for daily life and 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 work skills. Mental retardation occurs in 2.5-3% of the general population, and about 6-7.5 million mentally retarded individuals live in the United States alone.
In general, mentally retarded children reach developmental milestones such aswalking and talking much later than the general population. Symptoms may appear at birth or later in childhood, depending on the cause. Some cases of mild mental retardation are not diagnosed before the child enters preschool. 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 Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) classifies four different degrees of mental retardation:mild, moderate, severe, and profound. These categories are based on the individual's functioning level.
Approximately 85% of the mentally retarded population is in the mildly retarded category. Their IQ score ranges from 50-75, and they can often acquire academic skills up to the 6th grade level. They can become fairly self-sufficient and, in some cases, live independently with community and social support.
About 10% of the mentally retarded population is considered moderately retarded with IQ scores ranging from 35-55. 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 a supervised environment such as a group home.
About 3-4% of the mentally retarded population is severely retarded with IQ scores of 20-40. They may master very basic self-care skills and some communication skills. Many are able to live in a group home.
Only 1-2% of the mentally retarded population is classified as profoundly retarded with IQ scores under 20-25. They may be able to develop basic self-careand communication skills with appropriate support and training and need a high level of structure and supervision. Their retardation is often caused by an accompanying neurological disorder.
The American Association on Mental Retardation (AAMR) has developed another widely accepted diagnostic classification system for mental retardation that focuses on the capabilities of the retarded individual rather than on the limitations. The categories describe the level of support required. They are: intermittent support, limited support, extensive support, and pervasive support. Intermittent support, for example, is support needed only occasionally, perhaps during times of stress or crisis. It is the type of supporttypically required for most mildly retarded individuals. At the other end ofthe spectrum, pervasive support, or life-long, daily support for most adaptive areas, would be required for profoundly retarded individuals.
Aggression, self-injury, and mood disorders are sometimes associated with thedisability. The severity of the symptoms and the age at which they first appear depend on the cause. If retardation is caused by genetics in the form ofan inherited disorder, 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 35% of cases, the cause of mental retardation cannot be found. Biological and environmental factors include inherited abnormality of the genes, such as fragile X syndrome; single gene defects such as phenylketonuria (PKU);and accidents or mutations in genetic development such as the development ofan extra chromosome 18 (trisomy 18) and Down syndrome. Environmental factorsinclude cigarette smoking and drug abuse during pregnancy and fetal alcoholsyndrome (which affects one in 600 children in the United States and is caused by excessive alcohol intake in the first twelve weeks (trimester) of pregnancy. Some studies have shown that even mo! derate alcohol use during pregnancy may cause learning disabilities in children.
Maternal infections and illnesses such as glandular disorders, rubella, toxoplasmosis, and cytomegalovirus infection may cause mental retardation. When the mother has high blood pressure (hypertension) or blood poisoning (toxemia),the flow of oxygen to the fetus may be reduced, causing brain damage and mental retardation.
Birth defects that cause physical deformities of the head, brain, and centralnervous system frequently cause mental retardation. Neural tube defect, forexample, is a birth defect in which the neural tube that forms the spinal cord does not close completely. This defect may cause children to develop an accumulation of cerebrospinal fluid on the brain (hydrocephalus). Hydrocephaluscan cause learning impairment by putting pressure on the brain.
Hyperthyroidism, whooping cough, chickenpox, measles, and Hib disease (a bacterial infection) 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) cause swelling that, in turn, maycause brain damage and mental retardation. Traumatic brain injury caused by ablow or a violent shake to the head may also cause brain damage and mental retardation in children.
Ignored or neglected infants who are not provided the mental and physical stimulation required for normal development may suffer irreversible learning impairments. Children who live in poverty and suffer from malnutrition, unhealthy living conditions, and improper or inadequate medical care are at a higherrisk. Exposure to lead can also cause mental retardation. Many children havedeveloped lead poisoning by eating the flaking lead-based paint often found in older buildings.
Federal legislation entitles mentally retarded children to free testing and appropriate, individualized education and skills training within the school system from ages 3-21. For children under the age of three, many states have established early intervention programs that assess, recommend, and begin treatment programs. Many day schools are available to help train retarded childrenin basic skills such as bathing and feeding themselves. Extracurricular activities and social programs are also important in helping retarded children and adolescents 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 retardation. Mildly retarded individuals can often acquire the skills needed to live independently andhold an outside job. Moderate to profoundly retarded individuals usually require supervised community living.
Family therapy can help relatives of the mentally retarded develop coping skills. It can also help parents deal with feelings of guilt or anger. A supportive, warm home environment is essential to help the mentally retarded reach their full potential.
Individuals with mild to moderate mental retardation are frequently able to achieve some self-sufficiency and to lead happy and fulfilling lives. To reachthese 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 individuals have a shortened life expectancy. The diseases that are usually associated with severe retardation may cause the shorter life span. People with Down syndrome will develop the brain changes that characterize Alzheimer's diseasein later life and may develop the clinical symptoms of this disease as well.