Module 12: Mental Retardation (Intellectual Disability)

Intellectually Disabled Child and MotherMental Retardation (Intellectual Disability)

Mental retardation (MR), increasingly referred to as intellectual disability, can result from a variety of causes: congenital malformations, genetic, teratogenic, infectious, toxic, and perinatal factors, and postnatal complications. In one-quarter to one half of cases, it is impossible to attribute a particular child’s or adolescent’s MR to a single cause; in half of the children and adolescents for whom causal factors are known, there is more than one such factor (e.g., early bacterial meningitis and lack of intellectual stimulation in the home). The milder the MR, the more difficult it typically is to identify a specific etiology.

MR is defined as significant limitations in both intelligence and adaptive behavior, with onset before age 18. MR is characterized by significantly sub-average intellectual functioning (an intelligence quotient [IQ] of approximately 70 to 75 or below), existing concurrently with related limitations as expected for age and by the individual’s cultural group in two or more of the following applicable adaptive skill areas: communication, self-care, home living, social skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety. Mental retardation reflects the “fit” between the capabilities of individuals and the structure and expectations of their environment. A valid assessment considers cultural and linguistic diversity as well as differences in communications and behavioral factors.1, 2

The life functioning of a child or teen with MR will generally improve if she has adequate and appropriate support, or resources and strategies that promote her interests and welfare. To improve functioning, a child or teen may need intermittent, limited, extensive, or pervasive support depending on the severity of MR; the level of support needed varies from individual to individual and over time. Support should focus on personal needs and aspirations instead of deficits. Primary care providers need to work together with children and adolescents with MR and their families to establish goals and to ensure that these children, teens, and families have the support they need to achieve these goals.3

Key Facts:

  • Mental retardation is estimated to affect between 1 and 3 percent of the general population in the United States. It is approximately 1.5 times more common in males than females.4
  • Nearly 569,000 children ages 6 to 21 have some level of intellectual disability that qualifies them for special education services in school.5
  • Chromosomal mutations, such as Down syndrome and fragile X syndrome, and prenatal exposure to toxins, such as fetal alcohol spectrum disorder, are responsible for 30 percent of all identified cases of MR.6
  • The etiology of MR is known in approximately three-quarters of children and adolescents with severe MR and about half of children and adolescents with mild MR.4


  1. Schalock, R. L., Luckasson, R. A., & Shogren, K. A. (2007). The renaming of mental retardation: Understanding the change to the term intellectual disability. Intellectual and Developmental Disabilities, 45 (2), 116-124.
  2. American Psychiatric Association. (2000). Diagnostic and Statistical Manual of Mental Disorders (4th ed.). Washington, D.C.: American Psychiatric Association.
  3. Thompson, J. R., Hughes, C., Schalock, R. L., Silverman, W., Tassé, M. J., Bryant, B., et al. (2002). Integrating supports in assessment and planning. Mental Retardation, 40 (5), 390-405.
  4. Sadock, B. J., & Sadock, V. A. (2009). Kaplan and Sadock's Concise Textbook of Child and Adolescent Psychiatry. Philadelphia, PA: Lippincott Williams & Wilkins.
  5. Office of Special Education and Rehabilitative Services, Office of Special Education Programs. (2009). 28th annual report to Congress on the implementation of the Individuals with Disabilities Education Act, 2006, vol. 1. Washington, D.C.: U.S. Department of Education.
  6. Dulcan, M. K. (2009). Dulcan's Textbook of Child and Adolescent Psychiatry. Arlington, VA: American Psychiatric Publishing, Inc.

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