03/16/2026
What are Intellectual &
Developmental Disabilities (IDD)?
Intellectual & Developmental Disabilities is a term used when a person has certain limitations in mental functioning and in skills such as communicating, taking care of him or herself, and social skills. These limitations will cause a child to learn and develop more slowly than a typical child. Children with IDD may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating. They are likely to have trouble learning in school. They will learn, but it will take them longer. There may be some things they cannot learn.
What Causes these Disabilities?
The most common are causes of IDD are::
*Genetic conditions. Sometimes IDD 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).
* Problems during pregnancy. IDD can result when a baby does not develop inside the mother properly. For example, there may be a problem with the way the baby's cells divide as it grows. A woman who drinks alcohol or gets an infection like rubella during pregnancy may also have a baby with IDD.
* Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, he or she may have IDD.
* Health problems. Diseases like whooping cough, the measles, or meningitis can cause IDD. These disabilities can also be caused by extreme malnutrition (not eating right), not getting enough medical care, or by being exposed to poisons like lead or mercury.
IDD is not a disease. You can't catch it from anyone. IDD is also not a type of mental illness, like depression. There is no cure for IDD. However, most children with IDD can learn to do many things. It just takes them more time and effort than other children.
How are Intellectual and/or
Developmental Disabilities
Diagnosed?
IDD is diagnosed by looking at two main things. These are:
the ability of a person's brain to learn, think, solve problems, and make sense of the world (called IQ or intellectual functioning); and
whether the person has the skills he or she needs to live independently (called adaptive behavior or adaptive functioning).
Intellectual functioning, or IQ, is usually measured by a test called an IQ test. The average score is 100. People scoring below 70 to 75 are thought to have IDD. To measure adaptive behavior, professionals look at what a child can do in comparison to other children of his or her age. Certain skills are important to adaptive behavior. These are:
* daily living skills, such as getting dressed, going to the bathroom, and feeding one's self;
* communication skills, such as understanding what is said and being able to answer;
* social skills with peers, family members, adults, and others.
Providing services to help individuals with IDD has led to a new understanding of how we define these disabilities. After the initial diagnosis of IDD is made, we look at a person's strengths and weaknesses. We also look at how much support or help the person needs to get along at home, in school, and in the community. This approach gives a realistic picture of each individual. It also recognizes that the "picture" can change. As the person grows and learns, his or her ability to get along in the world grows as well.
What Are the Signs of Intellectual & Developmental Disabilities?
There are many signs of IDD. For example, children with these disabilities may:
* sit up, crawl, or walk later than other children;
* learn to talk later, or have trouble speaking,
* find it hard to remember things,
* not understand how to pay for things,
* have trouble understanding social rules,
* have trouble seeing the consequences of their actions,
* have trouble solving problems, and/or
* have trouble thinking logically
