Current clinical definition from Diagnostic and statistical manual of mental disorders DSM: A persistent pattern of inattention and/or hyperactivity/impulsivity that is more frequently display and more severe than is typically observed in individuals at a comparable level of development. There is only one ADHD and there are 3 subcategories of ADHD:

-Predominantly inattention presentation

-Predominantly hyperactive/impulsive presentation

-Presentation of hyperactive/impulsive and inattention.

The only variable in the disorder is in the severity of the symptomatic behaviours which is the directly resulting impairment in genetic and difficulties in brain development