mental retardation

Mental retardation

A developmental disability characterized by significantly subaverage general intellectual functioning, with concurrent deficits in adaptive behavior. The causes are many and include both genetic and environmental factors as well as interactions between the two. In most cases the diagnosis is not formally made until children have entered into school settings. In the preschool years, the diagnosis is more likely to be established by evidence of delayed maturation in the areas of sensory-motor, adaptive, cognitive, social, and verbal behaviors. By definition, evidence of mental retardation must exist prior to adulthood, where vocational limitation may be evident, but the need for supervision or support may persist beyond the usual age of social emancipation.

From the aspect of etiology, mental retardation can be classified by prenatal, perinatal, or postnatal onset. Prenatal causes include genetic disorders, syndromal disorders, and developmental disorders of brain formation. Upward of 700 genetic causes have been suggested as associated with the development of mental retardation. Many environmental influences on the developing fetus, for example, infection, and other unknown errors of development may account for mental retardation.

Perinatal causes include complications at birth, extreme prematurity, infections, and other neonatal disorders. Postnatal causes include trauma, infections, demyelinating and degenerative disorders, consequences of seizure disorders, toxic-metabolic disorders, malnutrition, and environmental deprivation. Often no specific cause can be identified for the mental retardation of a particular individual.

Individuals with mental retardation are typically subclassified in terms of the manifest severity of cognitive disability as reflected by the ratio of mental age to chronological age, or intelligence quotient (IQ). Subaverage intellectual functioning is defined as an IQ score of at least two standard deviations below the mean, or approximately 70 to 75 or below. Mild, moderate, severe, and profound degrees of mental retardation refer to two, three, four, or five standard deviations below the normal IQ for the general population.

Limitations in adaptive behavior must also be demonstrable in order to satisfy diagnostic criteria for mental retardation. This criterion is important because certain artistic or other gifts may not be revealed by formal IQ testing, and different levels of learning difficulty may be accentuated by the demands of specific environments. Outside such environments, an individual may navigate a normal course in life.

A specific genetic or other cause of mental retardation may also predispose to other medical or neurologic conditions. In these circumstances, the comorbid medical conditions may increase the likelihood of emotional or behavioral problems, or contribute to the challenges with which a given child must contend. Thus, the identification of cause can be important in planning for the medical, educational, and treatment needs of a particular individual.

Considerable progress has been made in both prevention and treatment. Diet is a method of treatment following early detection of phenylketonuria; warnings regarding alcohol consumption during pregnancy, lead exposure in infancy, and disease immunization and therapy are measures for prevention of retardation. Advances in prenatal, obstetrical, and neonatal care and genetic counseling have had the effect of reducing the incidence or the severity of various conditions. Energetic training and the application of psychosocial techniques have resulted in improved social performance and adaptive behavior in many persons with mental retardation.

mental retardation