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Causes of Attention-Deficit/ Hyperactivity Disorder (ADHD)

It is becoming increasingly clear that the symptoms of ADHD are associated with low activity of various brain centers that normally serve to focus attention on specific tasks and screen-out distractions [ref]. One brain area in particular, called the dorsal anterior cingulated cortex, seems to be important in quieting down the mind's background thoughts when concentration is needed to perform a particular task [ref]. This area has been shown to have reduced activity in ADHD [ref].

Dopamine is a neurotransmitter that plays a central role in the functioning of these brain centers. Brain imaging studies have shown that the lower the dopamine activity in these areas, the greater the level of Inattention symptoms of ADHD [ref]. This would explain why the principle medictions for ADHD are ones that increase dopamine activity.

These impairments seem to be due in large part to genetic factors, which accout for over half of the risk of developing ADHD [ref]. Many of the genes implicated in the transmission of ADHD are related to the dopamine neurotransmitter system [ref].

Several environmental factors have also been shown to lead to ADHD. These include [ref]: toxins in the food or water supply like lead, mercury and PCBs; pregnancy and delivery complications including low birth weight and fetal exposure to alcohol and maternal smoking; and childhood abuse. Growing up in poverty also raises the risk of developing ADHD [ref], perhaps by increasing the chances of the above environmental risk factors. Of note, dietary patterns, such as consuming large amounts of sugar or additives, does not contribute to ADHD, and nor does watching large amounts of television [ref].

 

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Diagnosis

Course & Prevalence