(May 01, 2006) -- It's known that lead exposure poses serious health risks, including cognitive function problems.

But new research suggests that certain children are more likely to develop attention-deficit hyperactivity disorder (ADHD) when exposed to lead in their environment.

The study found that youngsters with a specific genetic variation in a dopamine receptor, dubbed DRD4-7, had more problems with tasks that required attention and flexibility. The researchers also found that boys exposed to lead were at greater risk of attention problems than girls.

"Lead exposure leads to problems with attention and executive function. And certain kids are going to be more affected by the adverse effects of lead," said study author Dr. Tanya Froehlich, a developmental, behavioral and pediatric specialist at Cincinnati Children's Hospital Medical Center.

Froehlich was expected to present the findings Monday at the Pediatric Academic Societies annual meeting, in San Francisco.

An estimated 3 percent to 5 percent of American children -- 2 million -- have ADHD. Symptoms include the inability to pay attention, hyperactivity and impulsive behavior. The exact cause of ADHD isn't known, but there are numerous theories as to what contributes to its development. Environmental factors, such as lead exposure, have long been suspected of being a contributing factor, according to the National Institute of Mental Health.

Since lead exposure can contribute to problems with attention and executive function -- the ability to plan and organize behavior -- and people with ADHD also have problems with attention and executive function, the researchers thought there might be some genetic connection.

So, they looked at the dopamine receptor gene DRD4, because it had been previously associated with children with ADHD, Froehlich said.

In a group of 172 boys and girls, the researchers looked at the DRD4 gene and tested the children for lead at 60 months of age. Then at 66 months, the children were given ADHD tests.

Eight percent of the children were diagnosed with ADHD, but about one-quarter of the children showed symptoms of ADHD.

The researchers found two types of DRD4 variations -- a low-risk and a high-risk one. Children with the high-risk variation were more likely to have ADHD symptoms, such as problems with spatial working memory (the ability to keep information in mind while performing a complex task) and ";attentional flexibility" (the ability to change when you get new information or encounter an obstacle). Exposure to lead didn't seem to increase the symptoms in this group, however.

But in the low-risk group, whose members were less likely to have attention problems to start with, lead exposure significantly impaired their spatial working memory and attentional flexibility, the study found.

"In an environment contaminated with lead, a genetic variation that was protective becomes disadvantageous," Froehlich said.

The researchers also found that boys were more likely to suffer from lead's adverse effects. And, Froehlich noted, boys have higher rates of ADHD. "This could be one of the reasons why," she said.

Dr. Karen Ballaban-Gil, a pediatric neurologist at Montefiore Medical Center in New York City, said, "Lead exposure may have more cognitive consequences in a susceptible subset of the population."

"Parents need to be very vigilant about looking for homes that are free of lead. And it's not just houses -- lead can be in toys or ceramics, especially those bought outside of the U.S.," she said, adding that simple lead tests are available in stores.

"The most important thing is to prevent lead exposure in the first place," Froehlich said.

More information

To learn more about the effects of lead and steps you can take to minimize exposure, visit the U.S. Environmental Protection Agency.

Source: HealthDay News

Last updated: 05/06

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