ADHD Causes

The pathogenesis (cause) of ADHD has not been totally defined. One theory springs from observations regarding variations in functional brain-imaging studies between those with and without symptoms. Similar variations have been shown in studies of the structure of the brain of affected and nonaffected 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 a 92% probability of the same diagnosis in the twin sibling. When comparing nonidentical twin sibling subjects, the probability falls to 33%. Overall population incidence is 3%-10%.

Genes that control the relative levels of chemicals in the brain called neurotransmitters seem to be different in ADHD, and levels of these neurotransmitters are out of normal balance.

• MRI and other imaging studies suggest that these imbalances occur in parts of the brain that control certain types of movement and executive functions.



• These areas of the brain may be smaller and/or less active in people with ADHD.

The six major tasks of executive function that are most commonly distorted with ADHD are the following:

• shifting from one mindset or strategy to another (that is, flexibility);



• organization (for example, anticipating both needs and problems);



• planning (for example, goal setting);



• working memory (that is, receiving, storing, then retrieving information within short-term memory);



• separating emotions from reason; and



• regulating speech and movements appropriately.