The cause of ADHD has not been fully defined. One theory springs from
observations in functional brain imagining studies between those with
and without symptoms. However, other authorities point out that similar
variations have been shown in studies of the structure of the brain of
affected and non-affected individuals. Animal studies have
demonstrated differences in the chemistry of brain transmitters
involved with judgment, impulse control, alertness, planning, and
mental flexibility.
A genetic predisposition has been demonstrated in (identical) twin and sibling studies. If one identical twin is diagnosed with ADHD, there is at 92% probability of diagnosis with the twin sibling. When comparing nonidentical twin sibling subjects, the probability falls to 33%. (Overall population incidence is 8%-10% in the U.S., as described above.)
A genetic predisposition has been demonstrated in (identical) twin and sibling studies. If one identical twin is diagnosed with ADHD, there is at 92% probability of diagnosis with the twin sibling. When comparing nonidentical twin sibling subjects, the probability falls to 33%. (Overall population incidence is 8%-10% in the U.S., as described above.)
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