Mental Retardation: Overview and Diagnosis

William Otis Walker; Chris Plauché Johnson

doi:10.1542/pir.27-6-204

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William Otis Walker Jr, MD*
Chris Plauché Johnson, MEd, MD†

^*Director, Neurodevelopmental/Birth Defects Clinics, Children’s Hospital and Regional Medical Center, The University of Washington, Seattle, Wash
^†Professor, Department of Pediatrics, University of Texas Health Science Center at San Antonio, Texas

Note: This is part 1 of a 2-part article. Part 2 will appear in July 2006.

Objectives

After completing this article, readers should be able to:

Contrast the current criteria used by the American Association on Mental Retardation and the American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV-TR) to establish a diagnosis of mental retardation.
Characterize the relationship between the age of presentation and the severity level of mental retardation.
Recognize the importance of obtaining a detailed family history (three generations) as part of the etiologic evaluation of mental retardation.
Know the mechanism of inheritance for Fragile X.
List age-appropriate instruments for the measurement of intelligence and adaptive skills.

Introduction

Mental retardation (MR) is one of the more common developmental disabilities. It can be idiopathic and challenging to recognize in normal-appearing children who have developmental delays. Conversely, MR can be easily recognized when the child presents with dysmorphic features associated with a known genetic MR disorder. Mental retardation currently is defined by the American Association on Mental Retardation (AAMR) as “significantly sub-average general intellectual functioning accompanied by significant limitations in adaptive functioning in a least two of the following skills areas: communication, self-care, social skills, self-direction, academic skills, work, leisure, health and/or safety. These limitations manifest themselves before 18 years of age.” (1) Recognizing that a numerical value alone may be neither precise nor adequate to distinguish between the abilities of a child whose intelligence quotient (IQ) is 71 and one whose IQ is 69, the AAMR defines the upper limit of subaverage general intellectual functioning as “70 to 75” when there are also significant concerns regarding adaptive abilities. The American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders, 4th edition–Text Revision (DSM-IV-TR) definition of mental retardation differs from that of the AAMR in that its …