Etiology and Assessment

Abstract

Intellectual disability is a general term that describes intellectual capacity and adaptive functioning. There are many causes and many co-occurring conditions. To appreciate and respect the uniqueness of each individual and to choose appropriate interventions, it is critical that, if possible, the cause for intellectual disability be identified or the conditions that led to or sustain it be recognized. This chapter begins with an overview followed by an approach to understanding causation, a description of how etiology is determined, consideration of the neurobiological/environmental interface, a discussion of the evaluation process to determine causes and conditions related to diagnoses, and a discussion of risk factors. Intellectual disability is an intellectual, cognitive, and developmental disability that profoundly affects an individual’s functioning and adaptation to everyday life. Intellect refers to mental ability or capacity, the power of thought, and the ability to reason and solve problems. Mental capacity is distinguished from perception, emotions, and feelings. Intelligence refers to facility and quickness in understanding and problem solving. In intellectual disability, there is reduced mental capacity. Cognition refers to the use or handling of knowledge through mental activities associated with thinking, learning, and memory, which are necessary processes to acquire knowledge. In intellectual disability, there are cognitive disabilities that vary depending on the individual syndrome. The extent of intellectual disability varies among syndromes, and there may be variations within a syndrome. Both cognition and intellect are linked to cortical brain function. Intellectual disability is a developmental disability with onset during the developmental period. Thus, there are delays in meeting developmental mile stones in motor, fine motor, language, and psychosocial areas. Finally, there are difficulties in adaptive function and in the mastery of developmental tasks as a result of intellectual, cognitive, and developmental disabilities. A focus on the etiology of intellectual disability is needed for research, clinical, and administrative purposes. This chapter will review the multiple causes of intellectual disability, considering the interface between genetic, neurobiologic, and environmental factors and causation. It emphasizes the importance of a comprehensive evaluation and provides guidelines for conducting an evaluation. Associated mental, emotional, and behavioral disorders are discussed in chapter 6.