Neurodevelopmental disorders

Neurodevelopmental disorders are a group of disorders characterised by impairments of social, academic, or occupational functioning. By definition, the onset of all disorders listed under this category must be in early development, usually prior to school age. Grouped broadly, neurodevelopmental disorders are classified in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association, 2013) under the following six categories:

• intellectual disability

• neurodevelopmental communication disorders

• autism spectrum disorder (ASD)

• attention deficit hyperactivity disorder

• neurodevelopmental motor disorders

• specific learning disorder.

Intellectual disability has many causes and is heterogeneous in presentation. Neurodevelopmental intellectual disabilities include intellectual developmental disorder, which is characterised by deficits in intellectual and adaptive functioning (when compared to an individual's peers). The DSM-5 and International Statistical Classification of Diseases and Related Health Problems 2010 Edition (ICD-10; WHO, 2011) codes, respectively, for intellectual development disorder are 319 and F70–F73. Clinical assessment in addition to standardised intelligence testing is required to confirm deficit, and severity is rated on a four-point scale defined by differences in conceptual, social, and practical domains. Global developmental delay (GDD; 315.8 [F88]) is the diagnosis provided for children under the age of 5 years where assessment of functioning is unreliable and standardised testing is difficult. Nevertheless, development is considered delayed across all aforementioned areas and overall adaptive functioning is poor. Reassessment after a period of time to confirm diagnosis is required. Children who have sensory or physical impairments (such as vision or hearing loss, or a concurrent mental disorder) that render assessment of intelligence difficult may be diagnosed with unspecified intellectual disability (intellectual development disorder; 319 [F79]). However, this diagnosis is used only rarely and would also be in addition to poor adaptive functioning skills relative to similarly impaired peers. Due to the varying predictive validity of current assessments for children, particularly those under the age of 5, reassessment is required.

Neurodevelopmental communication disorders comprise deficits in speech (expressive means of communication), language (a structured system of communication including spoken and written words, sign language, pictures, or symbols) and communication (a method of having impact on another individual via verbal or non-verbal methods).