Intellectual Disability (Mental Retardation)

The approach to genetic testing in the evaluation of intellectual disability is changing with the introduction of newer techniques, such as microarray testing.After reading this article, readers should be able to:Intellectual disability is a general term for what has previously been described as mental retardation. ID is a lifelong condition characterized by significant impairment of cognitive and adaptive development owing to abnormalities of brain structure or function. ID is not a single entity, but rather a general symptom of neurologic dysfunction. At this time, the terminology used with respect to intellectual disability (ID) (mental retardation [MR]) is shifting. The term mental retardation is still in use in many settings, including by some clinicians, and is found in legal and public policies that determine eligibility for support; however, the use of the term intellectual disability as a direct substitute for mental retardation is increasing. The American Association on Mental Retardation has been renamed the American Association on Intellectual and Developmental Disabilities (AAIDD), while emphasizing that the definition of ID is exactly the same as that for MR. The chief reason for the change is that the term mental retardation is perceived as being pejorative; this semantic change does not reflect a reframing of the condition.It is anticipated the next iteration of the Diagnostic and Statistical Manual of Mental Disorders (DSM) will use a different term in place of MR; within this article, the term used is ID.There are two commonly used formal definitions for ID/MR. The definition for MR in the fourth edition of the DSM (DSM-IV) and the AAIDD definition for ID are worded slightly differently, but are essentially the same. Both base the definition on three coexisting features: (1) significantly subaverage intellectual functioning accompanied by (2) deficits or impairments in adaptive skills with (3) onset before 18 years of age.Degrees of MR (ID) are described within the DSM-IV. The correlating adjectives (mild, moderate, severe, profound) often are used in summarizing test results, and it is helpful to understand what they represent. Within the DSM, the ranges are given as intelligence quotient (IQ) numbers, which are based on the mean population IQ of 100, and 1 SD equals 15 points on commonly used assessments. A score of fewer than 70 points, ie, more than 2 SDs below the mean, represents ID. Mild ID is defined when the IQ falls 2 to 3 SDs below the mean (55 to 70). In moderate ID, the IQ is 3 to 4 SDs below the mean (40 to 55); in severe ID, the IQ is 4 to 5 SDs below the mean (25 to 40); and in profound ID the IQ is more than 5 SDs below the mean (below 25).The AAIDD definition of ID does not reference these categories. The emphasis within that framework is on the level of support needed by an individual in addition to limitations to cognition and adaptive functioning. A tool for classification that can be applied as an alternative is the International Classification of Functioning, Disability, and Health developed by the World Health Organization, which includes body function and structure, activities, social participation, and environmental factors.The descriptor borderline, as in borderline intelligence, or borderline ID/MR, is used sometimes to describe the situation where the IQ falls 1.5 to 2.0 SDs below the mean (70.0 to 77.5). Persons with that profile may have significant differences in function, especially in academics, but are not generally regarded as having ID.By convention, for all levels of ID, reduced IQ must be accompanied by deficits in adaptive functions, which include conceptual, social, and practical skills. Conceptual skills include language, literacy, and numeracy achievement, as well as understanding of time and money. Social skills include social judgment, interpersonal skills, and social problem solving. Practical skills include personal care and other activities of daily living, occupational skills, ability to negotiate the world safely and access transportation, and so forth.Clinicians vary with respect to application of the term ID (or MR) depending on the age of the individual. Some prefer to use the term developmental delay or global developmental delay for children younger than 5 years and reserve ID or MR for older children. For some, that usage appears to be a matter of convention, whereas for others it is a reflection of the need to have confidence in the developmental trajectory of a child before applying the latter terms. There has been a definition given to global developmental delay by the American Academy of Neurology and the Practice Committee of the Children Neurology Society, which has further complicated the understanding of terminology. Within that definition, a child must have significant delay (2 SDs or more below the mean on age-appropriate, standardized, norm-referenced testing) in any two or more areas of development, which means the term would apply to many children who do not go on to meet criteria for ID. Finally, many health care practitioners and families continue to use developmental delay rather than ID or MR on the basis of its being perceived as a more positive and less stigmatizing term.An individual with ID has delayed development, that is, the pattern and sequence follow a typical order but at a slower rate and with limitations with respect to the final level of achievement. This pattern is different from atypical development, in which children exhibit behaviors that fall outside of the normal, or expected, range of development. Children with autistic spectrum disorders develop atypically, and have qualitative differences in their ways of communicating and relating socially. They may or may not also show delayed development or ID.Estimates of the prevalence of ID vary from 1% to 3%, with the higher numbers likely representing cohorts defined only by IQ. Reports of actual measured prevalence vary with differences in the populations studied, case definitions, and study design. Most individuals with ID have IQs that fall in the mild range. ID is found more commonly in boys than in girls in a 1.4:1.0 ratio. Based on current population figures and using a 1% prevalence, there are currently more than 6 million American children and more than 600,000 Canadian children with ID.The age at identification typically reflects the degree of severity; that is, severely affected children typically are identified earlier because they fail to meet expected milestones in the first 2 years of life. Children with mild ID may not be identified until they have been in school for several years. Gross motor development frequently is within normal expectations in children who eventually are given a diagnosis of ID, whereas receptive language delay will virtually always be present. (In preschool children, receptive language is the best predictor of intelligence.) Some children with ID will be identified because of associated medical conditions, such as genetic syndromes.When ID has been identified, it is important to attempt to identify the cause (Table 1). Although it is not a common occurrence, there are situations in which a condition will be identified that will be treatable, such as certain inborn errors of metabolism. Identification of cause also may lead to recognition of associated health risks (eg, immune deficiency associated with 22q11 deletion syndrome) or have genetic implications for the affected individual and his family (eg, fragile X syndrome). Identification of a cause can also be helpful in allowing a family to understand the child and to plan for the future, and can assist families in accessing support systems, some of which are organized around specific etiologic conditions.In some cases, identification of the cause will be straightforward. In many children, however, no specific etiology will be identified. In those situations, the hunt for causation should be understood as an ongoing process because newer technologies may reveal answers that were not obtainable earlier. An excellent example of this evolution has been the impact of advanced genetic testing, such as microarray, on helping our understanding of the causes of ID.The literature varies widely with respect to the reported success rate for identifying the cause of developmental delay or ID. Some studies report yields in the neighborhood of 10% and others as as that a of of cause generally etiology based on including and or often is to when is can be that the is that may or may not be and that the latter is associated rather than identifying the etiology of the problem and the cause of the brain causes and genetic differences are the common causes of ID. X is the common to cause ID. The in 1 in boys and 1 in to and in some for 1% to of the in boys with ID. with fragile X typically have moderate ID, but the cognitive varies from disability to severe ID with or also can have fragile X X has the but their cognitive and typically are of girls with fragile X will have borderline intellectual function or mild with fragile X often have of a with a and They also may have such as and with and in boys with fragile X can include a and or and behaviors associated with spectrum such as and to with fragile X may or may not show such as may have in or social language including and spectrum and spectrum common cause of ID is or which the common A study found that the prevalence of in American children and years in (3) Intellectual function varies in with have a mild to moderate degree of ID. Some with have severe ID and also may have which further their adaptive common ID is affected are to as having spectrum The impact of varies and does not reflect the degree of in a however, current any The and are that but there also to be significant individual such as the age and social and to other The cognitive impact of is best defined in the population to have the on the basis of coexisting differences in and of include a a and and is that in to 2.0 in the Most children with have mild ID, some have and some will have moderate ID. function in children with is often further by coexisting and and social and the in the cause of a ID, by genetic The should include a family on identifying other including and who have conditions, as well as a of and The medical of neurologic and other and and a of and of the pattern and developmental trajectory are may be to a genetic (eg, and found in should be because to cause may be found in any of that may associated with ID include (eg, or and A neurologic may reveal or The should be by specific testing of and as of the for cause and because of the higher prevalence of is not for is because such as or abnormalities may assist with they may a or (eg, syndrome). the can support for pattern recognition using such as the in or for with a as with the the profile can its when at in with the and For children with often have a with in and language and in the and do not the cause of a ID, further should be to the with the emphasis on genetic for age or further by the or for and lead should be is not likely to be helpful there is further in the to a This is that in and the at some for such as in the that the need to disorders include developmental or and level of function, family severe and severe to profound levels of is not and should be for situations in which there is a of normal does not an genetic because the is normal in at of children with abnormalities and ID. The of has to the of what approach to use for genetic of the child with ID. approach for children with ID and a and has been to a and for fragile X For children with and normal on the and fragile X are normal, genetic evaluation with microarray not been approach to genetic testing is The of microarray in children with ID has been reported to be in and that of The of abnormalities with microarray has also been reported to with the of abnormalities abnormalities of and so Both the American of and The Canadian of in and that should be the for children with ID and should be of and in They that this testing should be only and that a there are to a common (eg, also that microarray is not the best is certain specific (eg, for which a in would be more can reveal and however, of the is not because these may be found in typically including family in some situations, and it is not always that the or is a genetic is in a child with ID, testing of and sometimes other family may be needed to in of the This testing may reveal genetic abnormalities in other family and also may reveal some cases, the family is of an genetic there are two or more affected with ID, and who are affected in a pattern that an a family of or a of genetic evaluation is In those situations, evaluation by a and advanced testing should be of any should not be until there has been with the family the child the implications of results, because may have and social in a child may have implications for other family For diagnosis of fragile X in a may the that in the family develop the fragile or fragile also can be genetic is the of in children with ID and normal has been reported to be in as many as of children in this (1) The are not typically such that they however, and may lead to more than on also or The is to an in this situation only on children with more severe of ID or may a cause by children will have specific that are of brain include such as or and especially can include such as or other on the neurologic For this should be is the as it will than there is no for the results, it is that the be 18 of because the may reveal that may be to identify earlier owing to of rather than also For the of is as in a in children with ID often significant or and the risks and always should be the cause of a ID be at the time of the it is important to may reveal that lead to such as the evolution of in in development, as well as in function or in may lead to such as in the of are to be for those with causes also is because for previously disorders with time (eg, for some children with ID are more likely to have 2 common for children with ID and their prevalence based on of the is important to health and development. there is coexisting for all can and should be including is not that with ID to for of however, understanding of the cognitive is more common in with ID and should be identified to direct Most with ID will have some of or a mental health at some in their is important to and for There is a that will the when is have a to in helping with ID, but they should not other and may a in Some individuals with mild ID can from cognitive and support from mental health in with ID should be common are from to to or to such as and in the definition of ID is the need for of intelligence as well as of adaptive function. is that be the language, and limitations of the individual being used should be those that have been widely and on a population that is an for the child being Most commonly used for are the intelligence Children 3 to years and 3 are with the and of 6 and years the for is often years and older can be with the There are a of other that may be used to individual including for children with language development. function can be by using such as the and the is in because of ID can have a impact on the child and The of intelligence testing with a age and is significantly the age of 4 years. that may intelligence test less of include the of an autistic as well as testing of a situation of significant environmental by impairment or motor impairments must be testing as should be by individuals who have with in individuals so should not be to a and testing will profile areas of and and should assist with and to The adaptive of the can be helpful for this An approach to and is important as Children and with ID from the support of a range of including occupational social and and and and and recognition of the that families in the success of their children is in the the of all children with including those with ID. The with Disabilities as the for Children all for to a public for all individuals with from age 3 to years that is to meet and for and In there is no this and individual have the understood to for with 15 of the of in for children before school are from that support or and widely with respect to and has been a from the of for individuals with ID. The for is of a of in the that all of the have and should be Most American and Canadian school use a of to include children and with ID in when and where The of this is still to because are and it is to for the many that can the of the in any school is of with of individuals who have mild ID within the and there can be no for any population of children from their The approach is to that and the of the individual children with ID are not best in a on activities and will have to their and skills by having at of their school in that are less conditions, such as or also may the need for does not to social especially in the and school years. Children with ID to and sometimes by as they the school years. that with and ID to can of children with ID they to be more likely to their others with identified and that children and with can those settings, such as are to be the best for a still can be in activities with other within the school with the has been a from as a for children in including those with ID. The of on in children with ID has not been well studied, but in studies of general populations of children, has been to and to children of with their with respect to and while to In the can for children with ID they have been in an and should be only when individual it such as when a is in the school is a time that can be in a more because has less impact on and owing to the and of to some be by the level of ID. 3 typical expectations for individuals with different levels of functioning. must be however, that individual and may these as will for and is important to the of expectations on and to individuals with ID, and must that may do it is to and develop his or and because these can have a positive impact on and of for skills is for for individuals with ID and should be an of their is at and of and use of Some children with ID will need to be with of may include language, systems, such as the or The of such as with the many that can support are alternative in the of the with Disabilities the of the of children with is to for and Although many individuals with ID will not or typical the they their and will assist in their of life. that must at the needed to within the and include and skills, personal skills, health care skills, and activities such as around the has been that of for with ID in with time skills, and these should be For those individuals with ID who have the needed should include skills for the and an of or An excellent for families and and health care is the developed by the in of of and based on a developed by the at the of at This a of skills that all should to and can be used to and skills are of for individuals with ID and should include the of social and and development is of the that should be to including those with ID. Health care can assist of in with children and with ID by helping to best to and with the the of in the of the with ID and his or family can also the care in understanding their of and to the and with ID are at for health and of health are For some these are by associated medical conditions, such as or however, and reduced access and use of health are more important often are not to include children and with ID, and may not be children develop often on of and other of associated with and reduced often is a Health care should be in that have been for such as with because the ranges on the reflect the actual population rather than the and include those who are and of should these in for families of individuals with ID to a family approach to and to for that can health areas have for children and with developmental such as the and these can an excellent of and for social development. with can be helpful in helping families with such and by helping health of individuals with ID is a In some cases, health is to to to typical In it may to health conditions, with or Some individuals with ID will not be of and or to can be of is often a time of for of children with ID. Most individuals with ID will go the of at the typical time, associated medical may such as in with some of such as Most individuals with ID negotiate with often is a for In who are able to their will be in and can be the and school commonly with is an of in a more typical that includes can be helpful to the there is significant change or of can the of and the of which also may assist with should at the risks and that substitute in this and any other situation must always on the of the individual for the are being of or with ID is is not a for or a substitute for of an individual with ID. There may be situations when an individual with ID will to as his or however, and in those situations it is that can be be an is more in the population with ID and often to be to the level of A for this is the for the for Children with Disabilities may need to understand that their children and with ID have typical is often a and should it The of is and use of where Social and can be helpful for and The that should not others others to in the areas that are by a are frequently the of or of their children and with ID. There is a at this time from on with ID to negotiate and as can for other of can be for with ID and those who support There are such as school and and eventually from school to however, can be such as the of school and or other in report or levels of at such as do with ID. A approach to and support often can such as from advanced the children and they will assist as well as time for and Children and with ID may from to and before the actual for to the school to meet and the excellent to support care and families around can be found the for have best around definition, ID is a condition that an individual the Persons with ID and their families should be to and to be that the that are needed to to the points for which they are are in is helpful for families and their to use those at the and the to next often is an important the school and typically is the or There are also of and of the need for or of that should be before they are the with ID the of where or will in the also will need and health can support families and with ID by to in the that can with these They can also to that the with ID has a and defined medical by of medical may have less direct in for with ID, and can by with such as the for Health of with Developmental or such as the for with care should for this especially are in a that still on the basis of perceived intellectual is not all have an to that including those with ID, an and health that the to and are always and that has the for a and at of development. can at the and levels by identifying areas where support or are needed and by with others to assist in those

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