Mental Retardation
Mental retardation is significantly subaverage intellectual functioning present from birth or early infancy, causing limitations in the ability to conduct normal activities of daily living.
Mental retardation is not a specific medical disorder like pneumonia or strep throat, and it is not a mental health disorder. A person with mental retardation has significantly below average intellectual functioning that limits his ability to cope with two or more activities of normal daily living (adaptive skills). These activities include the ability to communicate; live at home; take care of oneself, including making decisions; participate in leisure, social, school, and work activities; and be aware of personal health and safety.
People with mental retardation have varying degrees of impairment. While recognizing each person's individuality, doctors find it helpful to classify a person's level of functioning. Intellectual functioning levels can be based on the results of intelligence quotient (IQ) tests or on the level of support a person requires. Support is categorized as intermittent, limited, extensive, or pervasive. Intermittent means occasional support; limited means support such as a day program in a sheltered workshop; extensive means daily, ongoing support; pervasive means a high level of support for all activities of daily living, possibly including full-time nursing care.
Based only on IQ test scores, about 3% of the total population are considered to have mental retardation. However, if classification is based on the need for support, only about 1% of people have significant retardation.
 See the table Levels of Mental Retardation.
Causes
A wide variety of medical and environmental conditions can cause mental retardation. Some are genetic; some are present before or at the time of conception; others occur during pregnancy, during birth, or after birth. The common factor is that something interferes with the growth and development of the brain. However, doctors can identify a specific cause in only about one third of people with mild mental retardation and in two thirds of people with moderate to profound mental retardation.
 See the sidebar Some Causes of Mental Retardation.
Symptoms
Some children with mental retardation have abnormalities apparent at birth or shortly thereafter. These abnormalities may be physical as well as neurologic and may include unusual facial features, a head that is too large or too small, deformities of the hands or feet, and various other abnormalities. Sometimes such children have an outwardly normal appearance but have other signs of serious illness, such as seizures, lethargy, vomiting, abnormal urine odor, and failure to feed and grow normally. During their first year, many children with more severe mental retardation have delayed development of motor skills, being slow to roll, sit, and stand.
However, most children with mental retardation do not develop symptoms that are noticeable until the preschool period. Symptoms become apparent at a younger age in those more severely affected. Usually, the first problem parents notice is a delay in language development. Children with mental retardation are slower to use words, put words together, and speak in complete sentences. Their social development is sometimes slow, because of cognitive impairment and language deficiencies. Children with mental retardation may be slow to learn to dress and feed themselves. Some parents may not consider the possibility of retardation until the child is in school or preschool and is unable to keep up with age-appropriate expectations.
Children with mental retardation are somewhat more likely than other children to have behavioral problems, such as explosive outbursts, temper tantrums, and physically aggressive behavior. These behaviors are often related to specific frustrating situations compounded by an impaired ability to communicate and control impulses. Older children may be gullible and easily taken advantage of or led into minor misbehavior.
About 10 to 40% of people with mental retardation also have a mental health disorder (dual diagnosis). In particular, depression is common, especially in children who are aware that they are different from their peers or who are maligned and mistreated because of their disability.
Diagnosis
Many children are evaluated by teams of professionals, including a pediatric neurologist or developmental pediatrician, a psychologist, speech pathologist, occupational or physical therapist, special educator, social worker, or nurse.
Doctors evaluate a child suspected of having mental retardation by testing intellectual functioning and looking for a cause. Even though mental retardation is usually irreversible, identifying a disorder that caused the retardation may allow doctors to predict the child's future course, plan any interventions that can increase the child's level of functioning, and counsel parents on the risk of having another child with that disorder.
Newborns with physical abnormalities or other symptoms suggestive of a condition associated with mental retardation often need laboratory tests to help detect metabolic and genetic disorders. Imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI), may be performed to look for structural problems within the brain.
Some children who are delayed in learning language and mastering social skills have conditions other than mental retardation. Because hearing problems interfere with language and social development, a hearing evaluation is typically performed. Emotional problems and learning disorders also can be mistaken for mental retardation. Children who have been severely deprived of normal love and attention (see Section 23, Chapter 288) for long periods of time may appear retarded. A child with delays in sitting or walking (gross motor skills) or in manipulating objects (fine motor skills) may have a neurologic disorder not associated with mental retardation.
Because mild developmental problems are not always noticed by parents, doctors routinely perform developmental screening tests during well-child visits. Doctors use simple tests, such as the Denver Developmental Screening Test, to quickly evaluate the child's cognitive, verbal, and motor skills. Questions can be asked of the parents to help the doctor determine the child's level of functioning. Children who perform significantly below their age level on these screening tests are referred for formal testing.
Formal testing has three components: interviews with parents, observations of the child, and norm-referenced tests. Some tests, such as the Wechsler Intelligence Scale for Children-III (WISC-III), measure intellectual ability. Other tests, such as the Vineland Adaptive Behavior Scales, assess areas such as communication, daily living skills, social abilities, and motor skills. Generally, these formal tests accurately compare a child's intellectual and social abilities with those of others his age. However, children of different cultural backgrounds, non-English speaking families, and very low socioeconomic status are more likely to perform poorly on these tests. Because of this, a diagnosis of mental retardation requires that the doctor integrate the test data with information obtained from parents and direct observations of the child. A diagnosis of mental retardation is appropriate only when both intellectual and adaptive skills are significantly below average.
Prevention and Prognosis
Prevention mainly applies to genetic and infectious disorders and to accidental injuries. Doctors may recommend genetic testing for people with a family member or other child with a known inherited disorder, particularly ones related to mental retardation, such as phenylketonuria, Tay-Sachs disease, or fragile X syndrome. Identification of a gene for an inherited disorder allows genetic counselors to help parents evaluate the risk of having an affected child. Women who plan to get pregnant should receive necessary vaccinations, particularly against rubella. Women who are at risk for infectious disorders that may be harmful to a fetus, such as rubella and HIV, should be tested for these before getting pregnant.
Proper prenatal care lowers the risk of having a child with mental retardation. Folic acid, a vitamin supplement, taken before conception and early in pregnancy can help prevent certain kinds of brain abnormalities. Advances in the practices of labor and delivery and in the care of premature infants have helped to reduce the rate of mental retardation related to prematurity.
Certain tests, such as ultrasound, amniocentesis, chorionic villus sampling, and various blood tests, can be performed during pregnancy to identify conditions that often result in mental retardation. Amniocentesis or chorionic villus sampling is often used for women at high risk of having a baby with Down syndrome. A few conditions, such as hydrocephalus and severe Rh incompatibility (see Section 22, Chapter 258), may be treated during pregnancy. Most conditions, however, cannot be treated, and early recognition can serve only to prepare the parents and allow them to consider the option of abortion.
Because mental retardation sometimes coexists with serious physical problems, the life expectancy of children with mental retardation may be shortened, depending on the specific condition. In general, the more severe the retardation and the more physical problems the child has, the shorter the life expectancy. However, a child with mild mental retardation has a relatively normal life expectancy.
Treatment
The child with mental retardation is best cared for by a multidisciplinary team consisting of the primary care doctor, social workers, speech and physical therapists, psychologists, educators, and others. Together with the family, these people develop a comprehensive, individualized program for the child, which is begun as soon as the diagnosis of mental retardation is suspected. The parents and siblings of the child also need emotional support, and the whole family should be an integral part of the program.
The full array of a child's strengths and weaknesses must be considered in determining what kind of support is needed. Factors such as physical disabilities, personality problems, mental illness, and interpersonal skills all help determine how much support is needed.
All children with mental retardation benefit from education. The Federal Individuals with Disabilities Education Act requires public schools to provide free and appropriate education to children and adolescents with mental retardation or other developmental disorders. Education must be provided in the least restrictive, most inclusive setting possible--where the children have every opportunity to interact with non-disabled peers as well as equal access to community resources.
A child with mental retardation usually does best living at home. However, some families cannot provide care at home, especially for children with severe, complex disabilities. This decision is difficult and requires extensive discussion between the family and their entire support team. Having a child with severe disabilities at home can be disruptive and requires dedicated care that many parents may not be able to provide. The family may need psychologic support. A social worker can organize services to assist the family. Help can be provided by day care centers, housekeepers, child caregivers, and respite care facilities. Most adults with mental retardation live in community-based residences that provide services appropriate to the person's needs, with work and recreational opportunities.
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