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Developmental disabilities

Intellectual and developmental disabilities (IDDs) are a primary focus of the NICHD’s research support. IDDs include a variety of different types of disabilities and disorders, including those that affect the nervous system, metabolism, and cell function and survival.

The NICHD supports and conducts research to understand the causes and effects of IDDs and to help identify effective therapies for these disorders. The NICHD invests heavily in supporting many areas of IDD research, including the genetic and developmental causes of IDDs; the ways that IDDs affect learning, communication, cognition, and memory; interactions of the family and community with individuals with IDDs; and the effect of individual factors on social interactions, behavior, and emotions.

What are Intellectual and Developmental Disabilities (IDDs)?
Intellectual and developmental disabilities (IDDs) are disorders that are usually present at birth and that negatively affect the trajectory of the individual’s physical, intellectual, and/or emotional development. Many of these conditions affect multiple body parts or systems.

Intellectual disability starts any time before a child turns 18 and is characterized by problems with both:

  • Intellectual functioning or intelligence, which include the ability to learn, reason, problem solve, and other skills; and
  • Adaptive behavior, which includes everyday social and life skills.

The term "developmental disabilities" is a broader category of often lifelong disability that can be intellectual, physical, or both.

"IDD" is the term often used to describe situations in which intellectual disability and other disabilities are present.

It might be helpful to think about IDDs in terms of the body parts or systems they affect or how they occur. For example:
Nervous system. These disorders affect how the brain, spinal cord, and nervous system function, which can affect intelligence and learning. These conditions can also cause other problems such as behavioral disorders, speech or language difficulties, seizures, and trouble with movement. Cerebral palsy,5 Down syndrome, Fragile X syndrome, and autism spectrum disorders (ASDs) are examples of IDDs related to problems with the nervous system.
Sensory system. These disorders affect the senses (sight, hearing, touch, taste, and smell) or how the brain processes or interprets information from the senses. Preterm infants and infants exposed to infections, such as cytomegalovirus, may have problems with their eyesight and/or hearing. In addition, being touched or held can be difficult for people with ASDs.
Metabolism. These disorders affect how the body uses food and other materials for energy and growth. For example, how the body breaks down food during digestion is a metabolic process. Problems with these processes can upset the balance of materials available for the body to function properly. Too much of one thing, or too little of another can cause problems with overall body and brain function. Phenylketonuria (PKU) and congenital hypothyroidism are examples of metabolic conditions that can lead to IDDs.
Degenerative. Individuals with degenerative disorders may seem or be normal at birth and may develop normally for a time, but then they begin to lose skills, abilities, and functions because of the condition. In some cases, the problem may not be detected until the child is an adolescent or adult and starts to show signs of loss of function. Some degenerative disorders result from other conditions, such as untreated problems of metabolism.

The exact definition of IDD, as well as the different types or categories of IDD, may vary depending on the source of the information.

For example, within the context of education and the Individuals with Disabilities Education Act (IDEA), a law that aims to ensure educational services to children with disabilities throughout the nation, the definition of IDD and the types of conditions that are considered IDD might be different from the definitions and categories used by the Social Security Administration (SSA) to provide services and support for those with disabilities. These definitions and categories might also be different from those used by health care providers and researchers.

How many people are affected/at risk for IDDs?
The exact number of people affected by intellectual and developmental disabilities (IDDs) is unknown. This is because IDDs cover a wide range of conditions, many of which are diagnosed several years after birth, rather than in newborns.

Current estimates suggest that 2% to 3% of children in the United States have some form of intellectual disability.1

According to the Centers for Disease Control and Prevention (CDC), about 1 in 33 newborns (or 3%) in the United States are born with conditions related to problems in prenatal development.2

For current statistics on the number of children born with specific types of these conditions, visit the CDC Data and Statistics webpage on birth defects.

(1) American Academy of Pediatrics. (2012). Health issues: Intellectual disability. Retrieved August 9, 2012, from External Web Site Policy
(2) Centers for Disease Control and Prevention. (2008). Update on overall prevalence of major birth defects-Atlanta, Georgia, 1978-2005. Morbidity and Mortality Weekly Report, 57, 1-5. Retrieved August 9, 2012, from

What causes IDDs?
Intellectual and developmental disabilities (IDDs) have a variety of causes. Some possible causes include (but are not limited to):1,2,3

  • Genetic mutations, additions, or deletions: for example, most cases of Rett syndrome are caused by a change in the Methly-CpG-binding Protein 2 (MECP2) gene
  • Chromosome abnormalities, such as an extra chromosome or a missing chromosome: for example, Down syndrome [link to topic] results from having an extra copy or part of a copy of chromosome 21
  • Exposure to certain substances while in the womb: for example, exposure to alcohol while in the womb can result in fetal alcohol spectrum disorder
  • Infections during pregnancy: for example, infants whose mothers had cytomegalovirus during pregnancy may have hearing, vision, and neurological problems
  • Problems during childbirth: for example, an umbilical cord that gets wrapped around a baby’s neck during delivery could cut off the supply of blood and oxygen to the brain resulting in IDDs
  • Traumatic Brain Injury (TBI)
  • Preterm birth

(1) American Academy of Pediatrics. (July 30, 2012). Health issues: Outlook for children with intellectual disabilities. Retrieved August 9, 2012, from External Web Site Policy
(2) National Dissemination Center for Children with Disabilities (NICHCY). (January, 2011). NICHCY disability fact sheet #8: Intellectual disabilities. Retrieved August 9, 2012, from External Web Site Policy
(3) American Academy of Pediatrics. (July 30, 2012). Health issues: Intellectual disability. Retrieved August 9, 2012, from External Web Site Policy

How do health care providers diagnose IDDs?
The diagnosis of an intellectual disability is typically made through a test of intelligence or cognition, often assed by the range of scores on an Intelligence Quotient (IQ) test.1 This type of test will help the health care provider examine the ability of a person to learn, think, solve problems, and make sense of the world.2 Average IQ test score is around 100, while 85% of children with an intellectual disability score in the range of 55 to 70.3 More severe cases of intellectual disability generally have lower IQ scores.

Clinicians will also observe a child’s behavior for signs of a disability and assess adaptive behavior. Adaptive behaviors include coping skills and other behaviors that show how a child interacts with other people.2 Health care providers can use this information to assess whether the individual has the skills needed to live and interact well with others.

Some conditions that lead to IDDs may be diagnosed with a blood test, ultrasound, or another method, depending upon the condition. These tests may be conducted after birth or during pregnancy.

Newborn screening relies on testing blood samples taken from newborns while they are still in the hospital to help identify certain serious or life-threatening conditions, including some that lead to IDDs. Most tests use a few drops of blood obtained by pricking the infant’s heel. If a screening test suggests a problem, the infant’s doctor will follow up with further testing.4

To learn more about newborn screening, visit the Newborn Screening Translational Research Network website at or the Centers for Disease Control and Prevention webpage at

Prenatal Screening. Health care providers recommend that certain pregnant women, including those who are older than 35 years of age and those with a family history of certain conditions, have their fetuses tested for conditions that cause IDD prenatally, while the fetus is still in the womb. There are two main types of prenatal tests.

Amniocentesis. Amniocentesis (pronounced am-nee-oh-sen-TEE-sis) is a test that is usually performed to determine whether a fetus has a genetic disorder. In this test, a doctor takes a small amount of fluid from the womb using a long needle. The fluid, called amniotic (pronounced am-nee-OT-ik) fluid, contains cells that have genetic material that is the same as the fetus’s genetic material. A laboratory grows the cells and then examines their genetic material for any problems. Some IDDs that can be detected with amniocentesis are Down syndrome and certain types of muscular dystrophy.

Because amniocentesis can cause a miscarriage in about 1 out of 200 cases, it is usually only recommended for pregnancies in which the risk of genetic disorders or other problems is high.

Chorionic Villus Sampling (CVS) 5,6. This test extracts cells from inside the womb to determine whether the fetus has a genetic disorder. Using a long needle, the doctor takes cells from the chorionic villi (pronounced KOHR-ee-on-ik VILL-i), which are tissues in the placenta, the organ in the womb that nourishes the fetus. The genetic material in the chorionic villus cells is identical to that of the fetal cells.

Like amniocentesis, CVS can be used to test for chromosomal disorders such as Down syndrome and other genetic problems. CVS can be done earlier in pregnancy than amniocentesis, but it is also associated with a higher risk of miscarriage—about 1 in 100 cases. Health care providers usually only recommend CVS in women who are at high risk for a condition or IDD.

(1) American Academy of Pediatrics. (July 30, 2012). Health issues: Outlook for children with intellectual disabilities. Retrieved August 9, 2012, from External Web Site Policy
(2) National Dissemination Center for Children with Disabilities (NICHCY). (January, 2011). NICHCY disability fact sheet #8: Intellectual disabilities. Retrieved August 9, 2012, from External Web Site Policy
(3) American Academy of Pediatrics. (July 30, 2012). Health issues: Intellectual disability. Retrieved August 9, 2012, from External Web Site Policy
(4) National Library of Medicine, Medline Plus. (2012). On newborn screening. Retrieved August 25, 2012, from
(5) Simpson, J. L., & Otano, L. (2007). Prenatal genetic diagnosis. In S. G. Gabbe, J. R. Niebyl, & J. L. Simpson (Eds.), Obstetrics: Normal and problem pregnancies (5th ed.). New York, NY: Churchill Livingstone.
(6) American College of Obstetricians and Gynecologists. (2007). Invasive prenatal testing for aneuploidy. Washington, DC: Author. Retrieve September 14, 2014 from

What are treatments for IDDs?
Many intellectual and developmental disabilities (IDDs) have no cure, but there are often ways to treat their symptoms. For example:

  • Children with Down syndrome, fragile X syndrome, Rett syndrome, and other IDDs can often benefit from therapeutic speech therapy, occupational therapy, and exercises to improve their gross- and fine-motor skills. They might also be helped by special education and attention at school and by the efforts of parents, educators, and health care practitioners to encourage social contact and communication. In addition, for children with Down syndrome, surgery can help correct heart defects that may be present.
  • A variety of treatment options are available to help with the symptoms of autism spectrum disorders. Options may include behavioral, occupational, physical, and speech-language therapy. In addition, educational specialists can help guide the child’s school experiences.
  • Treatment for hypothyroidism, or underactive thyroid, includes daily oral hormone treatment.
  • The most effective treatment for phenylketonuria (PKU) is a special diet that carefully limits intake of the amino acid phenylalanine. People with PKU who begin this diet at birth or shortly thereafter develop normally and usually have no symptoms of PKU. It is important that individuals with PKU stay on the special diet through adolescence and that women with PKU continue the diet before and during pregnancy to promote the best health outcomes.

This information was developed by the National Institutes of Health, National Institute of Child Health and Human Development.

National Institute of Child Health and Human Development. Developmental Disabilities. Available at: Accessed February 7, 2014.

The information in this document is for general educational purposes only. It is not intended to substitute for personalized professional advice. Although the information was obtained from sources believed to be reliable, MedLink Corporation, its representatives, and the providers of the information do not guarantee its accuracy and disclaim responsibility for adverse consequences resulting from its use. For further information, consult a physician and the organization referred to herein.

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