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Attention-Deficit/Hyperactivity Disorder (ADHD) is a cluster of behaviors that emerge in childhood. To be diagnosed as ADHD one has to demonstrate inattention with hyperactivity or impulsivity. These behaviors have to be noted before seven years of age and last greater than six months. Also these behaviors have to present in two or more settings, such as home and school and cause impairment in social, academic and occupational pursuits.
Approximately three to five percent of school-age children are affected with ADHD and it develops in boys three times as often as in girls. Also, ADHD tends to be a chronic disease and most children continue to have symptoms as adults.
In contrast to most psychiatric conditions, ADHD has only been recognized recently. In 1902, the British physician George Still published the first descriptions of inattentiveness and hyperactivity in children with normal intellect. He attributed these behaviors to a lack of "inhibitory volition," which simply stated is will power. He postulated that brain damage was the culprit for this lack of will power.
The concept of brain damage as a cause of childhood inattention and activity was furthered by observations of children who recovered from the encephalitis (a viral infection of the brain) pandemic after World War I. Some of the children who recovered from these infections had behavior symptoms that resembled Still's findings. It was thought that the encephalitis caused some residual damage to the brain and was responsible for the children's behaviors. Thus, these children were termed suffering from "minimal brain damage."
However, in the late 1960s, the number of children diagnosed with minimal brain damage increased, and physicians could not find evidence of any brain damage in the majority of these children. Thus, the diagnosis changed to "hyperkinetic syndrome" to emphasize the symptoms rather than hypothesized cause. Later, specific criteria were outlined, and hyperkinetic syndrome evolved to "Attention Deficit Disorder" (ADD) to reflect these criteria. Due to that hyperactivity was noted in varying degrees in ADD patients, the diagnosis was changed to the current term, "Attention-Deficit/Hyperactivity Disorder."
Recent study of ADHD has revealed a genetic link in that if a family member has ADHD then the other family members have an increased risk of developing ADHD. Genetic studies have not implicated a specific gene as a cause, but most genes that have an association with ADHD help regulate the distribution of the neurotransmitter dopamine in various areas of the brain that are thought to regulate attention, planning and executing tasks, and impulsivity.
One of the more interesting hypotheses that has arisen as a result of these genetic discoveries is the concept that ADHD is much older than one hundred years and its existence could have served an adaptive function in human society. Hyperactivity, restlessness, and impulsivity are traits that would serve an explorer well. These traits may have served the general purpose of human migration and settlement. In sedentary contemporary society, these traits are not necessarily a boon and can cause havoc to individuals. Quelling this disruption is the goal of management of ADHD.