Attention-Deficit Hyperactivity Disorder - Risk Factors

Read our guide to learn more about the symptoms, prevalence and diagnosis of ADHD.

Causes

Brain Structure

Research using advanced imaging techniques shows there is a difference in the size of certain parts of the brain in children with ADHD compared to children who do not have ADHD. The areas showing change include the prefrontal cortex, the caudate nucleus and globus pallidus, and the cerebellum.

Brain Chemicals

Abnormal activity of certain brain chemicals in the prefrontal cortex may contribute to ADHD. The chemicals dopamine and norepinephrine are of special interest. Dopamine and norepinephrine are neurotransmitters (chemical messengers in the brain) that affect both mental and emotional functioning. They also play a role in the "reward response." This response occurs when a person experiences pleasure in response to certain stimuli (such as food or love). Studies suggest that increased levels of the brain chemicals glutamate, glutamine, and GABA -- collectively called Glx -- interact with the pathways that transport dopamine and norepinephrine.

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Nerve Pathways

Another area of interest is a network of nerves called the basal-ganglia thalamocortical pathways. Abnormalities along this neural route have been associated with ADHD, Tourette syndrome, and obsessive-compulsive disorders, all of which share certain symptoms.

Genetic Factors

Genetic factors most likely play a role in ADHD. The relatives of ADHD children (both boys and girls) have much higher rates of ADHD, antisocial, mood, anxiety, and substance abuse disorders than the families of non-ADHD children. Some twin studies report that up to 90% of children with a diagnosis of ADHD shared it with their twin.

Most of the research on the underlying genetic mechanisms targets the neurotransmitter dopamine. Variations in genes that regulate specific dopamine receptors have been identified in a high proportion of people with addictions and ADHD.

Review Date: 01/27/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).