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Attention-Deficit/Hyperactivity Disorder: Causes of ADHD

The exact causes of ADHD are not known.

Experts do know that ADHD has a strong genetic component. In addition, they think that genes that control the levels or functioning of certain chemicals in the brain called neurotransmitters seem to be different in those with ADHD.

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In some cases, though, there is no genetic link to ADHD, but other common behaviors,  such as smoking or drinking during pregnancy, as well as other obstetrical complications have been linked to ADHD in children.

Babies with low birth weight may have an increased risk of ADHD. The same is true for children who have had head injuries, particularly an injury to the frontal lobe. Young children who are exposed to lead or other environmental toxins such as PCBs or pesticides early in life may also have a higher risk of ADHD.

ADHD always begins in childhood before age 12. For some people, though, ADHD is not diagnosed until adulthood. That means adults who are newly diagnosed have actually had ADHD for years, and have had to endure symptoms as they've matured. In addition, research shows that between 30% and 70% of children with ADHD continue to have symptoms of the disorder when they become adults.

What is the genetic connection to ADHD?

ADHD tends to run in families. Studies have shown certain genetic characteristics that occur with high frequency in families where one or more family member has ADHD. Also, if one or both parents have ADHD, their children are more likely to develop the condition. And at least one-third of all fathers or mothers who had ADHD in their youth have children with ADHD.

What brain changes occur with ADHD?

Studies show that children and adults with ADHD tend to have abnormal functioning, or dysregulation, of certain brain chemicals known as neurotransmitters. There also tends to be abnormal functioning in the nerve pathways that regulate behavior. In addition, children with ADHD may have certain parts of the brain that are smaller or less active than they are in children who don't have ADHD.

Recent studies show that the brain chemical, dopamine, may play a role in ADHD. Dopamine is an important chemical that carries signals between nerves in the brain. It is linked to many functions, including movement, sleep, mood, attention, and learning.

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