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.
Intellectual disability is a neurodevelopmental disorder Definition of Developmental Disorders Developmental disorders are better called neurodevelopmental disorders. Neurodevelopmental disorders are neurologically based conditions that can interfere with the acquisition, retention, or... read more .
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 Children and Adolescents Several important mental health disorders, such as depression, anxiety disorders, and eating disorders, often start during childhood and adolescence. Some disorders, such as autism, start only... 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: Interpersonal skills, functional communication, social judgment, and awareness of others' thoughts and feelings
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.
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
Inherited disorders (such as phenylketonuria Phenylketonuria (PKU) Phenylketonuria is a disorder of amino acid metabolism that occurs in infants born without the ability to normally break down an amino acid called phenylalanine. Phenylalanine, which is toxic... read more , Tay-Sachs disease Tay-Sachs Disease and Sandhoff Disease Tay-Sachs disease and Sandhoff disease are types of lysosomal storage disorder called sphingolipidoses and are caused by a buildup of gangliosides in the tissues in the brain. These diseases... read more , neurofibromatosis Neurofibromatosis Neurofibromatosis is a group of genetic disorders in which many soft, fleshy growths of nerve tissue (neurofibromas) form under the skin and in other parts of the body, and flat spots that are... read more
, hypothyroidism Hypothyroidism in the Newborn Hypothyroidism is decreased production of thyroid hormone. Hypothyroidism in the newborn may occur if there is a structural problem with the thyroid gland. Symptoms may include delayed growth... read more , and Fragile X syndrome Fragile X Syndrome Fragile X syndrome is a genetic abnormality on the X chromosome that leads to intellectual disability and behavior problems. Chromosomes are structures within cells that contain DNA and many... read more )
Some causes that can occur during pregnancy include
Infections with human immunodeficiency virus Human Immunodeficiency Virus (HIV) Infection in Children and Adolescents Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and makes people more vulnerable to other infections and some cancers... read more , cytomegalovirus Cytomegalovirus (CMV) Infection in Newborns Cytomegalovirus is a common virus that usually causes few or no problems but can cause serious illness in infants who are infected before birth or around the time of birth. Cytomegalovirus infection... read more , herpes simplex virus Herpes Simplex Virus (HSV) Infection in Newborns Herpes simplex virus infection usually causes only annoying, recurring blisters in healthy adults but can cause severe infection in newborns. Newborns may become infected at birth or after birth... read more
, toxoplasmosis Toxoplasmosis in Newborns Toxoplasmosis is infection with the parasite Toxoplasma gondii. It usually does not cause problems in healthy adults, but it can cause serious illness in newborns and in people with a... read more , rubella Rubella in Newborns Rubella is a typically mild childhood viral infection that may, however, have devastating consequences for infants infected before birth. Rubella is caused by a virus. The fetus or newborn may... read more , or Zika virus Zika Virus Infection Zika virus infection is a mosquito-borne viral infection that typically causes no symptoms but can cause fever, rash, joint pain, or infection of the membrane that covers the white of the eye... read more 
Toxins (such as lead and methylmercury)
Drugs Drug Use 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 (such as phenytoin, valproate, isotretinoin, and cancer chemotherapy drugs)
Abnormal brain development Overview of Brain and Spinal Cord Birth Defects Birth defects of the brain and spinal cord can occur in early or late fetal development. Typical symptoms include intellectual disability, paralysis, incontinence, or loss of sensation in some... read more (such as porencephalic cyst, gray matter heterotopia, and encephalocele)
Preeclampsia Preeclampsia and Eclampsia Preeclampsia is new high blood pressure or worsening of existing high blood pressure that is accompanied by excess protein in the urine and that develops after the 20th week of pregnancy. Eclampsia... read more and multiple births Multiple Births The term multiple births refers to the presence of more than one fetus in the uterus. The number of twin, triplet, and other multiple births has been increasing during the last two decades.... read more (such as twins or triplets)
Some causes that can occur during birth include
Insufficient oxygen (hypoxia)
Some causes that can occur after birth include
Severe head injury
Undernutrition of the child
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.
About 20 to 35% of people with ID also have a mental health disorder Overview of Mental Health Disorders Children and Adolescents Several important mental health disorders, such as depression, anxiety disorders, and eating disorders, often start during childhood and adolescence. Some disorders, such as autism, start only... read more . In particular, anxiety Overview of Anxiety Disorders in Children and Adolescents Anxiety disorders are characterized by fear, worry, or dread that greatly impairs the ability to function and is out of proportion to the circumstances. There are many types of anxiety disorders... read more and depression Depression and Mood Dysregulation Disorder in Children and Adolescents Depression includes a feeling of sadness (or, in children and adolescents, irritability), and/or loss of interest in activities. In major depression, these symptoms last 2 weeks or more and... read more are common, especially in children who are aware that they are different from their peers or who are bullied and mistreated because of their disability.
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.
From birth on, growth and development Childhood Development Between the ages of 1 and 13, children's physical, intellectual, and emotional capabilities expand tremendously. Children progress from barely tottering to running, jumping, and playing organized... read more , including cognitive ability, are routinely assessed at well-child visits.
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 Screening for chromosomal abnormalities 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 
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 
, 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 , 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 
, 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 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 functional 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.
Imaging tests, such as magnetic resonance imaging (MRI) Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more 
, may be done to look for structural problems within the brain. An electroencephalogram (EEG) Electroencephalography Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more 
records the brain's electrical activity and is used to evaluate a child for possible seizures. X-rays of bones can also help rule out suspected causes of ID.
Genetic tests, such as chromosomal microarray analysis, may help identify disorders. Doctors may recommend genetic testing for people who have a family member or other child with a known inherited disorder, particularly ones related to ID, such as phenylketonuria Phenylketonuria (PKU) Phenylketonuria is a disorder of amino acid metabolism that occurs in infants born without the ability to normally break down an amino acid called phenylalanine. Phenylalanine, which is toxic... read more , Tay-Sachs disease Tay-Sachs Disease and Sandhoff Disease Tay-Sachs disease and Sandhoff disease are types of lysosomal storage disorder called sphingolipidoses and are caused by a buildup of gangliosides in the tissues in the brain. These diseases... read more , or Fragile X syndrome Fragile X Syndrome Fragile X syndrome is a genetic abnormality on the X chromosome that leads to intellectual disability and behavior problems. Chromosomes are structures within cells that contain DNA and many... read more . Identification of a gene for an inherited disorder allows genetic counselors to help parents evaluate the risk of having an affected child.
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 impairment refers to any degree of hearing loss, mild to severe, and can occur when there is a problem with a part of the ear, including the inner, middle, and outer ears, or the nerves... read more 
is typically done.
Emotional problems and learning disorders Learning Disorders Learning disorders involve an inability to acquire, retain, or broadly use specific skills or information, resulting from deficiencies in attention, memory, or reasoning and affecting academic... read more also can be mistaken for ID. Children who have been severely deprived of normal love and attention ( see Overview of Child Neglect and Abuse Overview of Child Neglect and Abuse Child maltreatment includes all types of abuse and neglect of a child under the age of 18 by a parent, caregiver, or another person in a custodial role (for example, clergy, coach, or teacher)... read more 
) for long periods of time may seem to have ID. 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 ID.
Prognosis for 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 more 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.
Women who plan to get pregnant should receive necessary vaccinations Overview of Immunization Immunization (vaccination) helps the body defend itself against diseases caused by certain bacteria or viruses. Immunity (the ability of the body to defend itself against diseases caused by... read more , particularly against rubella Prevention Rubella is a contagious viral infection that typically causes mild symptoms, such as joint pain and a rash, but can cause severe birth defects if the mother becomes infected with rubella during... read more 
. Women who are at risk of infectious diseases that may be harmful to a fetus, such as rubella Rubella Rubella is a contagious viral infection that typically causes mild symptoms, such as joint pain and a rash, but can cause severe birth defects if the mother becomes infected with rubella during... read more and human immunodeficiency virus Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more 
(HIV), should be tested before getting pregnant.
Proper prenatal care lowers the risk of having a child with ID. Folate (folic acid) Vitamins 
, a vitamin supplement taken before conception and early in pregnancy, can help prevent certain kinds of brain abnormalities, especially 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 .
Advances in the practices of labor and delivery and in the care of premature infants have helped to reduce the rate of ID related to prematurity Preterm (Premature) Newborns A preterm newborn is a baby delivered before 37 weeks of gestation. Depending on when they are born, preterm newborns have underdeveloped organs, which may not be ready to function outside of... read more .
A few conditions, such as hydrocephalus Hydrocephalus Hydrocephalus is an accumulation of extra fluid in the normal spaces within the brain (ventricles) and/or between the inner and middle layers of tissues that cover the brain (the subarachnoid... read more 
and severe Rh incompatibility Hemolytic Disease of the Fetus and Newborn Rh incompatibility occurs when a pregnant woman has Rh-negative blood and the fetus has Rh-positive blood. Rh incompatibility can result in destruction of the fetus’s red blood cells, sometimes... read more , 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 Abortion Induced abortion is the intentional ending of a pregnancy by surgery or drugs. A pregnancy may be ended by surgically removing the contents of the uterus or by taking certain drugs. Complications... read more .
Treatment of Intellectual Disability
Multidisciplinary support
A child with ID is best cared for by a multidisciplinary team consisting of the following:
Primary care doctor
Social workers
Speech pathologists
Audiologists
Neurologists or developmental pediatricians
Psychologists
Nutritionists
Teachers
Orthopedists
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 needs 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.
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.
More Information
The following are English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
Individuals with Disabilities Education Act (IDEA): A United States law that makes available free appropriate public education to eligible children with disabilities and ensures special education and related services to those children
March of Dimes: An organization aiming to improve the health of mothers and babies through research, advocacy, and education
Americans with Disability Act: A United States law that prohibits discrimination based on disability
Section 504 of the Rehabilitation Act: A United States law that guarantees certain rights to people who have disabilities
Drugs Mentioned In This Article
| Generic Name | Select Brand Names |
|---|---|
phenytoin |
Dilantin, Dilantin Infatabs, Dilantin-125, Phenytek |
folic acid |
Folacin , Folicet, Q-TABS |
