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Existing evidence suggests that genetic risk factors are critical to the development of attention deficit/hyperactivity disorder. Experts at Duke University Medical Center say that identification of the genes responsible is the first step towards earlier detection, prevention and, in the future, better treatments for AD/HD.

Allison Ashley-Koch, Ph.D., is a geneticist at the Duke Center for Human Genetics. She says AD/HD is believed to be one of the most heritable of all psychiatric conditions.

Siblings of individuals with AD/HD are about four times more likely to develop AD/HD than individuals with no family history of the disorder, she said. Similarly, many parents of individuals with AD/HD also suffer symptoms. However, adults often fail to recognize their own symptoms until after their child is diagnosed.

"It's estimated that up to 90 percent of the risk for developing AD/HD stems from genetic factors," Ashley-Koch said.

"AD/HD is a complex disorder likely influenced by many genes – some more important than others," she continued. "We expect these genes interact with each other and with environmental factors to trigger the development of AD/HD."

To tease out key AD/HD genes and important gene-gene and gene-environment interactions, the Duke Center for Human Genetics is enrolling children with AD/HD between the ages of 5 and 12 in a genetic study.

The research team collects detailed family, medical and environmental risk factor histories. Participants are also asked to complete a series of psychological and behavioral assessments. Blood samples are collected from the children with AD/HD and their parents, whenever possible. Samples may also be collected from siblings and other relatives, regardless of whether or not they show signs of AD/HD.

The team will follow study participants over time as their symptoms evolve, Ashley-Koch said. "We hope to not only identify candidate genes that predispose people to AD/HD, but also to identify genes that may differentiate distinct forms of the condition."

Three subtypes of AD/HD are recognized, she said. Some people exhibit primarily inattentive symptoms while others exhibit primarily hyperactive-impulsive symptoms. Still others struggle with both.

In addition, psychological conditions – such as anxiety, depression or oppositional defiance disorder -- often overlap with AD/HD symptoms, adding another layer of complexity, Ashley-Koch said.

"People with AD/HD can follow different trajectories over time," Ashley-Koch said. For example, a child may start out hyperactive, but then grow out of that particular symptom. "Separate genetic risk factors may underlie different aspects of the disorder."

The AD/HD study represents a collaboration between the Duke Center for Human Genetics, the Duke AD/HD Clinic and the University of North Carolina-Greensboro. To learn more about the genetics of AD/HD and ongoing studies, please contact the CHG at adhd@chg.duhs.duke.edu or toll-free at 1-866-DUK-ADHD (1-866-385-2343).