Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by executive dysfunction occasioning symptoms of inattention, hyperactivity, impulsivity and emotional dysregulation that are excessive and pervasive, impairing in multiple contexts, and developmentally-inappropriate. ADHD symptoms arise from executive dysfunction, and emotional dysregulation is often considered a core symptom. Impairments resulting from deficits in self-regulation such as time management, inhibition, and sustained attention can include poor professional performance, relationship difficulties, and numerous health risks, collectively predisposing to a diminished quality of life and a direct average reduction in life expectancy of 13 years. The disorder costs society hundreds of billions of US dollars each year, worldwide. It is associated with other neurodevelopmental and mental disorders as well as non-psychiatric disorders, which can cause additional impairment. While people with ADHD often struggle to initiate work and persist on tasks with delayed consequences, this may not be evident in contexts they find intrinsically interesting and immediately rewarding, potentiating hyperfocus (a more colloquial term) or perseverative responding. This mental state is often hard to disengage from and is related to risks such as for internet addiction and types of offending behaviour. ADHD represents the extreme lower end of the continuous dimensional trait (bell curve) of executive functioning and self-regulation, which is supported by twin, brain imaging and molecular genetic studies. The precise causes of ADHD are unknown in most individual cases. Meta-analyses of studies of twins, families and molecular genetics have shown that the disorder is primarily genetic with a heritability rate of 70-80%, where risk factors are highly accumulative. The environmental risks are not related to social or familial factors; they exert their effects very early in life, in the prenatal or early postnatal period. However, in rare cases, ADHD can be caused by a single event including traumatic brain injury, exposure to biohazards during pregnancy, or a major genetic mutation. There is no biologically distinct adult-onset ADHD except for when ADHD occurs after traumatic brain injury. Source: Wikipedia (en)