What are Intellectual and Developmental Disabilities?
There are many kinds of intellectual disabilities—and many causes. Intellectual disability is the most common developmental disability.
What are intellectual and developmental disabilities?
Intellectual and developmental disabilities (IDD) refer to “a group of developmental conditions characterized by significant impairment of cognitive functions, which are associated with limitations of learning, adaptive behavior and skills”.1
Developmental disabilities (DD) are defined by the Centers for Disease Control and Prevention as “a group of conditions due to an impairment in physical, learning, language, or behavior areas. These conditions begin during the developmental period, may impact day-to-day functioning, and usually last throughout a person’s lifetime”.2
Intellectual disability is the most common developmental disability.
Intellectual disability (ID) is defined by the Centers for Disease Control and Prevention as “a term used when there are limits to a person’s ability to learn at an expected level and function in daily life.”3
According to the American Association of Intellectual and Developmental Disabilities (AAIDD), an individual has ID if he or she demonstrates, before the age of 22:
- Limited intellectual functioning, as indicated by an IQ around 70
- Significant limitations in two or more adaptive areas (skills that are needed to live, work, and play in the community, such as communication or self-care)4
What is an Intellectual Disability?
Intellectual Disability
What is intellectual disability? Learn about what qualifies as an intellectual disability. Learn about skills that people with intellectual disability offer.
How does IDD happen?
There are a number of medical conditions associated with a diagnosis of IDD. For some people, the cause is unknown.
The most common causes of intellectual disabilities are:
The most common causes of intellectual disabilities are:
Genetic Conditions
Sometimes an intellectual disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. Examples of genetic conditions are Down syndrome, Fragile X syndrome, and phenylketonuria (PKU
Complications during pregnancy
An intellectual disability can result when the baby does not develop inside the mother properly. For example, there may be a problem with the way the baby’s cells divide. A woman who drinks alcohol or gets an infection like rubella during pregnancy may also have a baby with an intellectual disability.
Problems during birth
If there are complications during labor and birth, such as a baby not getting enough oxygen, he or she may have an intellectual disability.
Diseases or toxic exposure
Diseases like whooping cough, the measles, or meningitis can cause ID. They can also be caused by extreme malnutrition, not getting appropriate medical care, or by being exposed to poisons like lead or mercury.
How Common are Intellectual and Developmental Disabilities?
In 2019 there were an estimated 107.62 million individuals with intellectual disabilities globally, forming about 2% of the global population.5
That equates to approximately 6.5 million people in the United States with an intellectual disability.
That equates to approximately 6.5 million people in the United States with an intellectual disability.
16.6% of the population in the United States has any developmental disability (That equates to approximately 55 million people).
This number includes attention deficit/hyperactivity disorder (ADHD), learning disability, Autism Spectrum Disorder (ASD), intellectual disability, and other developmental delay. 6
This number includes attention deficit/hyperactivity disorder (ADHD), learning disability, Autism Spectrum Disorder (ASD), intellectual disability, and other developmental delay. 6
Intellectual disability often occurs alongside other developmental disabilities, like ASD. Significantly higher numbers of Black children with ASD are also diagnosed with ID, compared with Hispanic or White children.7
Learn More
The language we use is important. Read more about the language to use when referring to people with IDD.
Easy Read is a format of presenting information that is accessible to all people. Creating and using easy read language is one additional way that we can reach as wide an audience as possible.
There are many forms of IDD. Read more about different disabilities.