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 disability1 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.2
"IDD" is the term often used to describe situations in which intellectual disability and other disabilities are present.3
It might be helpful to think about IDDs in terms of the body parts or systems they affect or how they occur. For example4:
- 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,5Down 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.
For more information about disabilities included in IDEA, visit http://nichcy.org/disability/categories 
. For information about SSA and disabilities, visit https://www.ssa.gov/planners/disability/.
- Centers for Disease Control and Prevention. (n.d.). Intellectual disability fact sheet. Retrieved August 9, 2012, from http://www.cdc.gov/ncbddd/actearly/pdf/parents_pdfs/IntellectualDisability.pdf (PDF - 64 KB)
- American Association on Intellectual and Developmental Disabilities (n.d.). Retrieved September 14, 2012, from http://www.aaidd.org/content_100.cfm?navID=21
- American Association on Intellectual and Developmental Disabilities (n.d.). Retrieved September 14, 2012, from http://www.aaidd.org/content_104.cfm?navID=22
- National Dissemination Center for Children with Disabilities (NICHCY). (2011). NICHCY disability fact sheet #8: Intellectual disabilities. Retrieved August 9, 2012, from http://nichcy.org/disability/specific/intellectual
- Centers for Disease Control and Prevention. (May 18, 2012). Cerebral palsy: Facts about cerebral palsy. Retrieved August 12, 2012, from http://www.cdc.gov/ncbddd/cp/facts.html
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