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ADHD is "Real"
[August, 2007] Attention-deficit/hyperactivity disorder (ADHD) is an identifiable disease linked to changes in production of the brain chemical dopamine, two new reports suggest. Dopamine is a chemical substance, called a neurotransmitter, found in the brain that regulates movement, balance, and walking. ![]() ADHD is the most prevalent psychiatric disorder among children. "Despite decades of research, the specific neurobiological mechanisms underlying this disorder still remain unclear," the study authors write. "Genetic, clinical, and imaging studies point to a disruption of the brain dopamine system, which is corroborated by the clinical effectiveness of stimulant drugs (methylphenidate hydrochloride and amphetamine), which increase extracellular dopamine in the brain." What is the genetic component?In the first report, researchers found that a version of the dopamine receptor gene may help cause ADHD, but may also improve the disease's outcome. "If you have a certain variant of this gene, you have a greatly increased risk of having ADHD," says head researcher, Dr. Philip Shaw, from the Child Psychiatry Branch at the US National Institute of Mental Health. Dr. Shaw also states, "The kids who had the risk gene tended to get better. They also tended to be a little bit more intelligent." Not all children with the gene variant had ADHD. But it was present in one-quarter to one-fifth of children with ADHD. This is higher than the general population, of which one-fifth to one-sixth has the genetic variant. Gene Linked to Brain ScansDr. Shaw's team discovered the genetic variability by comparing 105 children with ADHD to 103 children who did not have the disorder. The children, who averaged 10 years of age, had magnetic resonance imaging (MRI) brain scans and DNA testing. Also, 67 of the children with ADHD were evaluated six years later. The gene variant was found in the dopamine D4 receptor gene (DRD4), associated with ADHD. This form of the gene is also linked with thinner tissues in certain areas of the brain that control attention. In the children followed for six years, those who had the gene variant present had better outcomes and regained healthy tissue thickness in the affected brain region. This finding may help explain how ADHD tends to improve with age, notes the research team. Dr. Shaw states, "This is a very important study as it adds increasing evidence that ADHD is a heritable [can be inherited] disease with genetically determined neurobiological underpinnings and adds further evidence that this is a valid mental disorder, often requiring neurobiological interventions [such as] pharmacological treatment." Surprising Dopamine ResultsIn the second study, led by Dr. Nora D. Volkow, of the US National Institute on Drug Abuse, researchers discovered that, in contrast to common belief, ADHD is associated with lowered dopamine production, instead of higher production. The study found that adults with ADHD who received the drug methylphenidate (Ritalin) had a blunted response to the medication. Dr. Volkow noted that "Individuals with ADHD have a decreased function of the brain dopamine system. ADHD, clearly, is associated with a biochemical dysfunction." This knowledge is important because it defends against the myth that ADHD is a disorder created in order "to sell medication," Dr. Volkow reports. This research supports the premise that stimulant medications, such as Ritalin, are beneficial because they increase the dopamine function in the brain, researchers say. Both reports were published in a recent issue of the Archives of General Psychiatry. Risk of Substance Abuse HigherDr. Volkow also notes that drugs such as nicotine, cocaine, and methamphetamine also improve dopamine function. "This may be the reason why individuals that have ADHD are at a much greater risk of abusing substances than the general population, because drugs of abuse increase dopamine brain function, and they will 'feel better,'" Dr. Volkow said. Always consult your physician for more information. |
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