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Developmental disability is an umbrella term that includes several types of lifelong and often severe disabilities that occur before the age of 22. Some developmental disabilities are largely physical in nature, such as osteogenesis imperfecta, cerebral palsy, and dwarfism. Others involve both physical and intellectual disability, such as Down syndrome and fetal alcohol syndrome. Others are intellectual disorders, such as autism spectrum disorder. Developmental disabilities that affect cognitive function are identified as intellectual disability (Centers for Disease Control and Prevention [CDC], n.d.-h; Schalock et al., 2012).

Intellectual disability is not a single disorder. Rather, the term is used to describe general symptoms of neurologic dysfunction (Shea, 2012). An intellectual disability is a developmental disability that occurs before the age of 18 and involves impaired intellectual functioning, a limited ability to function in daily life, and an impaired ability to learn, reason, and problem-solve. Additionally, intellectual disability is characterized by limited adaptive behavior, including a range of everyday social and practical skills (CDC, n.d.-e; Schalock et al., 2012).

Definitions of intellectual and developmental disabilities (IDDs) differ somewhat from one source to the other.

Intellectual disability is broadly related to thought processes and is characterized by significant limitations in intellectual functioning and adaptive behavior. These can be categorized as follows (Schalock et al., 2012):

  • Conceptual skills: These are the language and literacy skills used to manage money and time, understand number concepts, and be self-directive.

  • Social skills: These include interpersonal skills and self-esteem, as well as an understanding of concepts like social responsibility and social problem-solving; the ability to follow rules, obey laws, and avoid being victimized; and a lack of gullibility and naïveté (in other words, a healthy sense of wariness).

  • Practical skills: These include skills needed to carry out activities of daily living (personal care), occupational skills, skills to access healthcare, skills to travel or use transportation, the ability to maintain schedules and routines, money skills, the ability to use the telephone, and safety skills.

By definition, intellectual disability occurs any time before the age of 18. However, it is often diagnosed or observed soon after birth or during early childhood—although it is not diagnosed in some children until they are in school. Children with intellectual disability tend to have difficulty learning to speak, walk, dress, and eat without assistance, and have difficulty learning in school. Children with intellectual disability may be slower or fail in achieving developmental milestones expected of children (CDC, n.d.-b). Children and adults with intellectual disability often have difficulty letting others know their needs and wants, and many are unable to take care of themselves.

Although these disabilities are lifelong, functioning of many people with intellectual disability can be enhanced through appropriate supports, including early interventions (Schalock et al., 2012). There are varying degrees of intellectual disability, from mild to profound. Many people with intellectual disability can and do ...

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