31Neurodevelopmental
Disorders
The neurodevelopmental  disorders are a group of co nditions with onset in the
developmental period. The diso rders typically manifest early in development, often be-
fore the child enters grade school, and are characterized by developmental deficits that
produce impairments of person al, social, academic, or occupational functioning. The
range of developmental deficits varies from very  specific limitations of  learning or control
of executive functions to glob al impairments of social skills  or intelligence. The neurode-
velopmental disorders frequent ly co-occur; for example, in dividuals with autism spec-
trum disorder often have intellectual disability (intellectual developmental disorder), and
many children with attention-deficit/hyperactivity disorder (ADHD) also have a specific
learning disorder. For some diso rders, the clinical presentation includes symptoms of ex-
cess as well as deficits and delays in achiev ing expected milestones. For example, autism
spectrum disorder is diagnose d only when the characteristic deficits of social communi-
cation are accompanied by excessively repetitive  behaviors, restricted interests, and insis-
tence on sameness. 
Intellectual disability (intel lectual developmental disorder) is characterized by deficits
in general mental abilities, such as reasoning, problem solving, planning, abstract thinking,
judgment, academic learning, and learning from experience. The deficits result in impair-
ments of adaptive functioning, such that the individual fails to meet standards of personal
independence and social responsibility in one or more aspects of daily life, including com-
munication, social participation, academic or occupational functionin g, and personal inde-
pendence at home or in community settings . Global developmental delay, as its name
implies, is diagnosed when an individual fa ils to meet expected developmental milestones