Tufts OpenCourseware
Authors: John Morgan, Bonnie F. Zimble

Mental Retardation: Definitions

What is Mental Retardation and What Causes It?

Special Care in Dentistry
John Morgan, DDS
Tufts University School of Dental Medicine, 2008

Study Questions:

  1. What types of limitations are associated with mental retardation?
  2. Why is the term “mental retardation” often avoided? Why is its use sometimes necessary?
  3. Describe the four general causes of mental retardation.
  4. Describe the two types of functioning that are assessed when diagnosing mental retardation.

What is Mental Retardation?

Mental retardation 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 mental retardation may take longer to learn to speak, walk, and take care of their personal needs, such as dressing or eating. They are also likely to have trouble learning in school. They will learn, but it will take them longer. There may be some things they cannot learn.”      National Dissemination Center for Children with Disabilities.


For a more formal definition, and a great deal more information, please refer to the website run by The Arc, a long-standing national advocacy organization in the field of mental retardation. Their web site is at: http://www.thearc.org.  We will reference other The Arc online articles in this unit! 


Should we use the term “mental retardation?”

The Arc does not use the term “mental retardation” in their mission statement. Rather, they say that they ... 

“…work to include children and adults with cognitive, intellectual and developmental disabilities in every community.”

The term “mental retardation” is offensive to many people, and is best avoided whenever possible. However, as The ARC points out, in some states, the diagnosis and label “mental retardation” is needed to provide eligibility for special protections and services. For this reason, and for brevity, we will use the term “mental retardation” in this course.

What Causes Mental Retardation?

From the National Dissemination Center for Children with Disabilities 

“Doctors have found many causes of mental retardation.  The most common are: 

  • Genetic conditions.  Sometimes mental retardation is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons.  Examples of genetic conditions are:
  • Problems during pregnancy.  Mental retardation can result when a fetus does not develop properly in utero. For example, there may be a problem with the way the fetus'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 mental retardation.
  • Problems at birth.  If a baby has problems during labor and birth, causing anoxia, he or she may have mental retardation.
  • Health problems.  Diseases like whooping cough, the measles, or meningitis can cause mental retardation.  Mental retardation can also be caused by extreme malnutrition, insufficient medical care, or exposure to poisons like lead or mercury.

Mental retardation is not a disease.  Mental retardation is also not a type of mental illness, like depression.  While strategies for education, training and habilitation have been perfected through decades of research, there is no cure for mental retardation.”