The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5; American Psychiatric Association, 2013) defines an intellectual disability as “a disorder with onset during the developmental period that includes both intellectual and adaptive functioning deficits in conceptual, social, and practical domains” (p. 33). In other words, it is a disorder that forms before age 18 that affects a person’s intellectual development and ability to effectively use life skills. The term intellectual disability has replaced the term mental retardation in this edition of the DSM-5. Intellectual disabilities may occur alone or as a part of genetic syndromes or other developmental disabilities (see below) such as Down syndrome, Prader-Willi Syndrome, or autism spectrum disorder (ASD).