Concept of Childhood Mental Retardation

Childhood Disorders: Mental Retardation

Concept of Mental Retardation

Following are the basic concepts of mental retardation and the psychiatric approaches to it:

·   Mental retardation is not a single, specific disorder. The term refers to a behavioral syndrome, describing the level of a per-son’s functioning in defined domains. It does not have a single cause, mechanism, course, or prognosis and does not neces-sarily last a lifetime.

·   Mental retardation is not a unitary concept. Persons diagnosed as having mental retardation do not constitute a homogeneous group but represent a wide spectrum of abilities, clinical pres-entations and behavioral patterns.

·   Persons with mental retardation do not have unique person-alities or behavioral patterns that are specific to mental retar-dation, although certain patterns may be frequently seen in certain mental retardation-associated syndromes.

·   Maladaptive behaviors should not automatically be seen as part of the retardation or an expression of “organicity”. As in all individuals, these behaviors may be related to life experi-ences; they can also be a symptom of mental illness comorbid with the mental retardation.

·   Mental disorders seen in persons with mental retardation are the same as those in the general population.

Some common misconceptions about mental retardation are that it is a specific and lifelong disorder with unique person-ality pattern, and that comorbid mental disorders existing with mental retardation are different from those encountered in other individuals. Although mental retardation is listed as a mental disorder in the Diagnostic and Statistical Manual of Mental Dis-orders, Fourth Edition, Text Revision (DSM-IV-TR) (American Psychiatric Association, 2000), it is not a unique nosological en-tity. Instead, diagnosis of mental retardation refers to the level of a person’s intellectual and adaptive functioning below a cutoff point that is not even natural but is arbitrarily chosen in rela-tion to the average level of functioning of the population at large. Its chief function is administrative, defining a group of persons who are in need of support and educational services. Thus, men-tal retardation does not have a single cause, mechanism, course, or prognosis. It has to be differentiated from the diagnosis (if known) of the underlying medical condition.

Epidemiology of Mental Retardation

Prevalence

The results of epidemiological studies of mental retardation de-pend on two major factors: the definition of mental retardation that is used and how the results are ascertained. There have been various models for estimating the prevalence of mental retarda-tion. A model based on IQ score alone used the expected statisti-cal distribution of intelligence levels. The past definition based only on an IQ that was one standard deviation or greater below the mean implied that almost 15% of the population could be clas-sified as having mental retardation. With the introduction of the diagnostic criterion of impairment in adaptive behavior and an IQ cutoff at two standard deviations below the mean (approximately 70), the prevalence of mental retardation was commonly thought to be 3% of the population. More recent population-based studies, using multiple methods of ascertainment and a current definition of mental retardation, suggest that the prevalence might be closer to 1%. In the study of McLaren and Bryson (1987), the preva-lence of mild mental retardation was 0.37 to 0.59%, whereas the prevalence of moderate, severe and profound retardation was 0.3 to 0.4%. When age is considered, the highest prevalence is in the school-age group, when the child cannot meet the expectations of academic learning. United States Department of Education indi-cated the prevalence of mental retardation among school-age chil-dren (6–17 years of age) to be 1.14%, with variations reported by different states (Massey and McDermott, 1995). Conversely, some persons who are diagnosed with mild mental retardation when of school age lose that diagnosis in adulthood when their good adap-tive skills are more relevant than their academic achievement.