Classification and diagnosis

This chapter is divided in two parts. The first part describes the process of recent developments in the classification of Mental Retardation. It emphasizes the work of the World Health Organization (WHO) International Advisory Group for the revision of classification and diagnostic criteria of Mental Retardation in the International Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10; World Health Organization 1992a, 1992b) (WHO-IAGRMR), the Intellectual Disability section of the World Psychiatric Association (WPA-SPID), and the terminology adopted in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition by the American Psychiatric Association (APA) (DSM-5; American Psychiatric Association, 2013). Though the new International Classification of Diseases, Eleventh Edition (ICD-11) is not released at the time this book goes to print, we have described the debate that has taken place and the expected terminology to be finally adopted (World Health Organization, 2011). The second part of this chapter deals with the issue of diagnosis, including arguments for inclusion or not of certain criteria. The importance of taking into consideration the adaptive function in addition to symptoms and behaviors is discussed, as well as the diagnostic challenges for comorbid situations of intellectual disabilities and autism spectrum disorders or different behavioral phenotypes.