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Intellectual Disability

By

Stephen Brian Sulkes

, MD, Golisano Children’s Hospital at Strong, University of Rochester School of Medicine and Dentistry

Last full review/revision May 2020
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Intellectual disability is significantly below average intellectual functioning present from birth or early infancy, causing limitations in the ability to conduct normal activities of daily living.

  • Intellectual disability can be genetic or the result of a disorder that interferes with brain development.

  • Most children with intellectual disability do not develop noticeable symptoms until they are in preschool.

  • The diagnosis is based on the results of formal testing.

  • Proper prenatal care lowers the risk of having a child with intellectual disability.

  • Support from many specialists, therapy, and special education help children achieve the highest level of functioning possible.

The previously used term mental retardation has acquired an undesirable social stigma, so health care practitioners have replaced it with the term intellectual disability.

Intellectual disability (ID) is not a specific medical disorder like pneumonia or strep throat, and it is not a mental health disorder Overview of Mental Health Disorders in Children The treatment section for bipolar disorder has been extensively revised with separate treatment sections for mania and for depression. In addition, information has been added throughout to address... read more . People with ID have significantly below average intellectual functioning that is severe enough to limit their ability to cope with one or more areas of normal daily living (adaptive skills) to such a degree that they require ongoing support. Adaptive skills may be categorized into several areas including

  • Conceptual area: Competence in memory, reading, writing, and math

  • Social area: Awareness of others' thoughts and feelings, interpersonal skills, and social judgment

  • Practical area: Personal care, task organization (for work or school), money management, and health and safety

People with intellectual disability have varying degrees of impairment, classified from mild to profound. Although fundamentally impairment is caused by the decreased intellectual functioning (typically measured by standardized intelligence tests), the impact on the person's life depends more on the amount of support the person requires. For example, a person who has only mild impairment on an intelligence test may have such poor adaptive skills that extensive support is required.

Support is categorized as

  • Intermittent: Occasional support needed

  • Limited: Support such as a day program in a sheltered workshop

  • Extensive: Daily, ongoing support

  • Pervasive: High level of support for all activities of daily living, possibly including extensive nursing care

Based only on IQ test scores, about 3% of the population has intellectual disability (an IQ of less than 70). If classification is based on the need for support, only about 1% of the population has severe intellectual disability.

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Causes of Intellectual Disability

A wide variety of medical and environmental conditions can cause intellectual disability. Some conditions are genetic. Some are present before or at the time of conception, and others occur during pregnancy, during birth, or after birth. The common factor is that something interferes with the growth and development of the brain. Even with recent advances in genetics, especially techniques of chromosome analysis, a specific cause of ID often cannot be identified.

Some causes that can occur before or at conception include

Some causes that can occur during pregnancy include

Some causes that can occur during birth include

Some causes that can occur after birth include

Symptoms of Intellectual Disability

Some children with intellectual disability may 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, malformations of the hands or feet, and various other abnormalities. Sometimes 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 ID have delayed development of motor skills, and are slow to roll, sit, and stand.

However, most children with ID 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 ID 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 ID may be slow to learn to dress and feed themselves. Some parents may not consider the possibility of cognitive impairment until the child is in school or preschool and is unable to keep up with age-appropriate expectations.

Children with ID are somewhat more likely than other children to have behavioral problems, such as explosive outbursts, temper tantrums, and physically aggressive or self-injurious 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.

Diagnosis of Intellectual Disability

  • Prenatal screening

  • Developmental screening

  • Formal intellectual and skills testing

  • Imaging tests

  • Genetic and other laboratory tests

Screening before birth (prenatal screening) can be done to determine whether the fetus has certain abnormalities, including certain genetic disorders, that may cause intellectual disability.

When doctors suspect intellectual disability, children are evaluated by teams of professionals, including early intervention or school staff, a primary care doctor, a pediatric neurologist or developmental pediatrician, a psychologist, speech pathologist, occupational or physical therapist, special educator, social worker, or nurse. These professionals evaluate a child suspected of having intellectual disability by testing intellectual functioning and looking for a cause.

Even though the cause of the child's ID may be irreversible, identifying a disorder that caused the disability may allow doctors to predict the child's future course, prevent further loss of skills, 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.

Prenatal screening

Certain tests, such as ultrasonography Ultrasonography Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more , amniocentesis Amniocentesis Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more , chorionic villus sampling Chorionic Villus Sampling Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more , and various blood tests such as quad screening Triple and quad screening Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more , can be done during pregnancy to identify conditions that often result in ID. Amniocentesis or chorionic villus sampling is often done for pregnant women over 35 years of age because they have an increased risk of having a baby with Down syndrome Down Syndrome (Trisomy 21) Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome 21... read more Down Syndrome (Trisomy 21) and for pregnant women who have a family history of metabolic disorders. The quad screen is a test done in most pregnant women. It is done to measure levels of four substances in a woman's blood. The results of this test help doctors evaluate whether the fetus has an increased risk of having certain conditions, such as Down syndrome, trisomy 18 Trisomy 18 Trisomy 18 is a chromosomal disorder caused by an extra chromosome 18 that results in intellectual disability and physical abnormalities. Trisomy 18 caused by an extra chromosome 18. Infants... read more Trisomy 18 , or neural tube defects Neural Tube Defects and Spina Bifida Neural tube defects are a certain type of birth defect of the brain, spine, and/or spinal cord. Neural tube defects can result in nerve damage, learning disabilities, paralysis, and death. The... read more .

Measuring the mother's blood level of alpha-fetoprotein Second-Trimester Screening Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more is a helpful screening test for neural tube defects Neural Tube Defects and Spina Bifida Neural tube defects are a certain type of birth defect of the brain, spine, and/or spinal cord. Neural tube defects can result in nerve damage, learning disabilities, paralysis, and death. The... read more , Down syndrome Down Syndrome (Trisomy 21) Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome 21... read more Down Syndrome (Trisomy 21) , and other abnormalities. Noninvasive prenatal screening (NIPS) detects small amounts of DNA from the fetus in the mother's blood and uses that to diagnose genetic disorders in the fetus such as trisomy 21 (Down syndrome), trisomy 13 Trisomy 13 Trisomy 13 is a chromosomal disorder caused by an extra chromosome 13 that results in severe intellectual disability and physical abnormalities. Trisomy 13 is caused by an extra chromosome 13... read more Trisomy 13 , or trisomy 18 Trisomy 18 Trisomy 18 is a chromosomal disorder caused by an extra chromosome 18 that results in intellectual disability and physical abnormalities. Trisomy 18 caused by an extra chromosome 18. Infants... read more Trisomy 18 and certain other chromosome disorders.

Developmental screening

Because mild developmental problems are not always noticed by parents, doctors routinely do developmental screening tests during well-child visits. Doctors use simple questionnaires, such as the Ages and Stages Questionnaires or Child Development Inventories, to quickly evaluate the child's cognitive, verbal, and motor skills. Parents can help the doctor determine the child's level of functioning by completing a Parents' Evaluation of Developmental Status (PEDS) test. Children who perform significantly below their age level on these screening tests are referred for formal testing.

Formal intellectual and skills testing

Formal testing has three components:

  • Interviews with parents

  • Observations of the child

  • Tests in which the child's performance is compared with scores of many children of the same age

Some tests, such as the Stanford-Binet Intelligence Test and the Wechsler Intelligence Scale for Children, are done to measure intellectual ability. Other tests, such as the Vineland Adaptive Behavior Scales, are done to 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 in the same age group (called norm-referenced tests). However, children of different cultural backgrounds, non–English-speaking families, and very low socioeconomic status are more likely to do poorly on these tests. For these reasons, a diagnosis of ID requires that the doctor integrate the test data with information obtained from parents and direct observations of the child. A diagnosis of ID is appropriate only when both intellectual and adaptive skills are significantly below average.

Identifying the cause

Newborns with physical abnormalities or other symptoms suggestive of a condition associated with intellectual disability often need certain tests.

Other urine and blood tests are done depending on what doctors suspect is the cause.

Some children who are delayed in learning language and mastering social skills have conditions other than ID. Because hearing problems interfere with language and social development, a hearing evaluation Screening and Diagnosis Hearing loss in newborns most commonly results from cytomegalovirus infection or genetic defects and in older children results from ear infections or earwax. If children do not respond to sounds... read more Screening and Diagnosis is typically done.

Prognosis of Intellectual Disability

A person with mild ID has a relatively normal life expectancy, and health care is improving long-term health outcomes for people with all types of intellectual disabilities. Many people with ID can support themselves, can live independently, and can be successfully employed with appropriate support.

Because intellectual disability sometimes coexists with serious physical problems, the life expectancy of people with ID may be shortened, depending on the specific condition. People with more severe intellectual disability are likely to require support for life. In general, the more severe the cognitive disability and the more physical problems the person has, the shorter the life expectancy.

Prevention of Intellectual Disability

Fetal alcohol spectrum disorders Alcohol during pregnancy More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy... read more is a highly common and totally preventable cause of intellectual disability. The March of Dimes and other groups concerned about the prevention of ID focus much of their efforts on alerting women to the seriously damaging effects of drinking alcohol during pregnancy.

Treatment of Intellectual Disability

  • Multidisciplinary support

A child with ID is best cared for by a multidisciplinary team consisting of the following:

Other professionals may also be part of the team if necessary. Together with the family, these people develop a comprehensive, individualized program for the child that is begun as soon as the diagnosis of ID is suspected. The parents and siblings of the child also need emotional support and sometimes counseling. The whole family should be an integral part of the program.

The full array of a person'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 are all taken into consideration. People with ID and coexisting mental health disorders such as depression may be given appropriate drugs in dosages similar to those given to those without ID. However, giving a child drugs without doing behavioral therapy and making environmental changes is usually not helpful.

All children with ID benefit from special education. The federal Individuals with Disabilities Education Act (IDEA) requires public schools to provide free and appropriate education to children and adolescents with ID or other developmental disorders. Education must be provided in the least restrictive, most inclusive setting possible—that is, a setting where the children have every opportunity to interact with nondisabled peers and have equal access to community resources. The Americans with Disability Act and Section 504 of the Rehabilitation Act also provide for accommodations in schools and other public settings.

Did You Know...

  • The federal Individuals with Disabilities Education Act (IDEA) requires public schools to provide free and appropriate education to children and adolescents with intellectual disability or other developmental disorders.

A child with intellectual disability usually does best living at home. However, some families cannot provide care at home, especially for children with severe, complex disabilities or behavior concerns. This decision is difficult and requires extensive discussion between the family and their entire support team. 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 care givers, and respite care facilities. Most adults with ID live in community-based residences that provide services appropriate to the person's needs, as well as work and recreational opportunities.

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Drugs Mentioned In This Article

Generic Name Select Brand Names
SOTRET
DILANTIN
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