The diagnostic term 'mental retardation' is finally being eliminated in the upcoming international classifications of diseases and disorders. The term 'mental retardation' was introduced by the American Association on Mental Retardation in 1961 and soon afterwards was adopted by the American Psychiatric Association (APA) in its Diagnostic and Statistical Manual for Mental Disorders (DSM-5).[1,2] Mental retardation replaced older terms such as feeblemindedness, idiocy, and mental subnormality that had become pejorative. Now, over 5 decades later, the term 'mental retardation' is being eliminated for similar reasons.

The APA's fifth revision of its DSM-5[3] and the WHO in the 11th edition of the International Classification of Diseases (lCD-11) will revise their terminology.[4] This is consistent with the abandonment of the term by medical and educational professions and advocacy groups over recent years. The International Association for the Scientific Study of Mental Deficiency (IASSMD) has long been designated the International Association for the Scientific Study of Intellectual Disability (IASSID). The Journal of Mental Deficiency Research is now The Journal of Intellectual Disability Research and the federal advisory group The United States President's Committee on Mental Retardation is now designated The President's Committee for Persons With Intellectual Disabilities. In the United States, a federal statute (Public Law 111-256, Rosa's law) replaces the term 'mental retardation' with 'intellectual disability'[5] and requires that person first language be used when referring to those affected in all federal laws. Rosa's law is indicative of the sentiment for change. Rosa Marcellino, an 8-year-old girl with Down Syndrome from Maryland, was taunted frequently and pejoratively called 'retard' in a demeaning manner. With support from her state representative and US Senator Barbara Mikulski, legislation was initiated leading to the change in the law. Such change is important not only to deal with the pejorative use of the term, but also to emphasize that these are people with neurodevelopmental disorders requiring intervention early in the developmental period.

The ICD-11 working group proposes replacing mental retardation with intellectual developmental disorders (IDDs), a term it defines as 'a group of developmental conditions characterized by significant impairment of cognitive functions, which are associated with limitations of learning, adaptive behavior and skills'.[4] The new term proposed for DSM-5 is intellectual disability (ID)/IDD. The new DSM-5 category is synonymous with the proposed ICD-11 diagnosis of IDDs, in that it refers to a health condition or disorder.[4] It is semantically similar to the term 'intellectual disability' as used by the American Association on Intellectual and Developmental Disabilities (AAIDD), where the term 'belongs within the general construct of disability that has evolved over the past 2 decades'.[6] In the ICD-11 proposal, IDD as a health condition or disorder refers to a 'syndromic grouping or meta-syndrome that is analogous to the construct of dementia (major neurocognitive disorder in DSM-5), which is characterized by a deficit in cognitive functioning prior to the acquisition of skills through learning'.[4] Thus, IDD is classified as a neurodevelopmental disorder of brain development and contrasted with the DSM-5 category 'Neurocognitive Disorder' (in DSM-IV, dementia), in which onset is in late life. In major neurocognitive disorder, there is loss of cognitive capacity and loss of acquired cognitive skills; degeneration is a feature. In IDD, there are deficits in the cognitive capacity beginning in the early developmental period. In contrast, the term 'intellectual disability' as used by the AAIDD is a functional disorder, explicitly based on the WHO International Classification of Functioning (ICF).

The Working Group on the Classification of Intellectual Disabilities for ICD-11 conducted extensive literature reviews using a mixed qualitative approach in reviewing them, and followed up in a series of meetings of experts to produce consensus-based recommendations combining prior expert knowledge and available evidence.[4] For DSM-5, the neurodevelopmental workgroup followed similar procedures with literature review and expert opinion to reach consensus. No field trials were conducted. DSM-5 will be released in May 2013, but ICD-11 is not scheduled for release until 2015.

Critical components of intelligence proposed in both DSM-5 and the ICD-11 are verbal comprehension, working memory, perceptual reasoning, and cognitive efficacy. The diagnosis in DSM-5 will emphasize both clinical judgment and standardized intelligence testing; however, less emphasis is expected to be placed on the IQ score, but greater emphasis will be placed on the adaptive reasoning in academic, social, and practical settings. The requirement for both intellectual deficits and adaptive deficits that fail to meet the standards for personal independence are proposed to remain in DSM-5, with greater emphasis on linking intellectual deficits to adaptive deficits through adaptive reasoning in the three domains listed.

The DSM-5 is not a multiaxial classification as was DSM-IVTR. Thus, the proposed diagnostic term 'intellectual disability/intellectual developmental disorder' will no longer be on Axis II, but instead listed along with other mental disorder diagnoses. Consistent with this change, a definition of intelligence is proposed for inclusion in the definition. This change is believed necessary to focus on ID/IDD as a clinical entity and facilitate the clinical interview. Both DSM-5 and the AAIDD refer to the mainstream science definition of intelligence. This consensus definition defines intelligence as a general mental ability that involves reasoning, problem solving, planning, thinking abstractly, comprehending complex ideas, judgment, academic learning, and learning from experience.[7] Moreover, as noted, the proposed plan in DSM-5 is to incorporate a focus on adaptive reasoning in three contexts: academic learning, social understanding, and practical understanding.[8] Schalock[9] refers to this approach as the multidimensionality approach to ID. It is one that is increasingly of interest in determining how best to operationally define ID from cognitive and adaptive perspectives.[10]

Mental retardation has long been divided into four levels of severity reflecting the extent of intellectual impairment: mild, moderate, severe, or profound. These levels of severity are proposed to remain unchanged in ICD-11.[4] In DSM-5, the proposal is to use specifiers instead of subtypes to designate the extent of adaptive dysfunction in academic, social, and practical domains. The AAIDD[6] using a disability model focuses instead on the extent of disability in various settings and considers the supports needed to normalize an individual's life to the extent it is possible.

All of the definitions of an ID (DSM, ICD, and AAIDD) include, and will continue to require, deficits in intellectual and adaptive function; however, each provides a different emphasis, so it is important to be familiar with each of them. In applying these definitions, it is important to remember that specific adaptive abilities often coexist with strengths in other adaptive skills or personal capabilities; therefore, adaptive strengths must be carefully considered in the treatment planning.

Changes proposed for DSM-5 are pertinent to forensic psychiatry in the United States, where the IQ test number has often been used inappropriately to define a person's overall ability in forensic cases without adequately considering adaptive intellectual functioning. Appropriate diagnosis of ID/IDD has become more important in the United States because of the 2002 Supreme Court decision in Atkins vs. Virginia. In that case, it was decided that the execution of people with mental retardation met the United States Constitution's Eighth Amendment criteria that forbid cruel and unusual punishments.[11,12] This decision has resulted in placing greater emphasis in assessment on both cognitive and adaptive capacities for people with an ID. Despite the Supreme Court finding in this test case, Atkins, whose initial IQ was 59, when retested after several years in prison scored above 70, making him again eligible for the death penalty under Virginia law. His case highlights the importance of measuring adaptive intelligence and functioning in making the diagnosis. Fortunately for Atkins, there was prosecutorial misconduct sufficient to prevent his execution; he was given life imprisonment. In forensic situations, a multidimensional[9] model as proposed for DSM-5 that considers adaptive intelligence in academic, social, and practical domains may be more appropriate than the DSM-IVTR definition. Moreover, credulity and gullibility in persons with an ID are pertinent psychological constructs to consider in both community settings and forensic cases. Those affected often are unaware of risk and in many circumstances may lack common sense.[13,14] Thus, greater emphasis on both cognitive deficits and adaptive reasoning is needed in forensic settings.

Finally, psychiatric disorders are three to four times higher in people with an ID diagnosis than in the general population.[2] When criteria are met, both diagnoses should be made. There is some concern that the elimination of the multiaxial classification and removal of Axis II in DSM-5 may result in the diagnosis of an ID being overlooked without the requirement to always consider an Axis II diagnosis. Thus, it is critical to remember when assessing patients with mental disorders that ID should be considered as potentially co-occurring. When assessing for psychiatric disorders in people with an ID, assessment procedures must be modified to take into account associated disorders, such as communication disorders, autism spectrum disorder, and motor, sensory, or other co-occurring conditions. Knowledgeable informants are essential during assessment to identify changes in irritability, mood regulation, increased aggression, eating problems, sleep problems, and changes in adaptive behavior at work, at home, and in the community settings. Moreover, the prognosis and outcome of mental disorder diagnoses may be influenced by the presence of ID.

Co-occurring diagnoses to consider are major depressive disorder, which may occur throughout the range of severity of ID, attention deficit hyperactivity disorder, bipolar disorders (with and without aggression), anxiety disorders, autism spectrum disorder, impulse control disorders, major neurocognitive disorder, and stereotypic movement disorder (with or without self-injurious behavior).[2] Self-injurious behavior requires prompt diagnostic attention and may warrant a separate diagnosis of stereotypic movement disorder. Individuals with severe ID are more likely to demonstrate self-injury, aggression, and disruptive behaviors. Finally, individuals with a diagnosis of ID with co-occurring mental disorders are at risk for suicide attempts and may die from them.[15] Thus, screening for suicidal thoughts is essential in the assessment process.