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A study by researchers at Oregon Health & Science University proved a link between lead and ADHD.

(The Oregonian/OregonLive)

Lead, even in amounts well below levels considered safe for children, is directly associated with attention deficit hyperactivity disorder, a new study found.

Researchers at Oregon Health & Science University studied nearly 400 children between the ages of 6 and 17 years old, including half who were diagnosed with ADHD. They found that those with a certain gene mutation and ADHD had more severe symptoms. The gene appears to protect against lead damage.

Past research has associated lead with ADHD but this study, published in Psychological Science, confirms a tie between the two, said Joel Nigg, lead investigator and director of OHSU's ADHD program.

"One of the myths about ADHD is that this is just a genetic condition," Nigg said. "While we know genes play a role, we're proving that environmental pollutants are part of the story."

Lead is a neurotoxin that poses a particular threat to children and fetuses, causing learning and attention problems and lower IQs. At high levels, lead can cause seizures, coma or death. Though U.S. environmental regulations have reduced the amount of lead in the environment, for example in paint and gasoline, children can still be exposed by drinking water from aging lead pipes and by exposure to lead paint and dirt in school yards and to some imported toys and costume jewelry.

Though the Centers for Disease Control and Prevention has not established a safe lead level in children, the agency considers anything above 5 micrograms per deciliter of blood, or 50 parts per million, too high.

In Oregon, about 12,000 children younger than 6 are tested each year. Between 80 and 100 have levels higher than 5 micrograms per deciliter.

The children in the study had a little less than 1 microgram per deciliter or 10 parts per million, similar to the population average, Nigg said.

The children in the study were in Michigan, which has surveyed a random sample of residents for the gene, HFE C282Y. The study group had the same proportion of kids with the gene - 10 percent. That and their lead level made them a representative sample in terms of their genetics and exposure, Nigg said.

Although some ADHD research involving lead has been based on surveys, the children in the study went through detailed evaluations for the disorder. That included parent-teacher ratings, interviews, observations and psychological tests. The data were reviewed by a licensed psychiatrist and child psychologist who were unaware of the children's lead levels or the purpose of the study.

"The diagnosis was bulletproof," Nigg said.

The evaluations confirmed that children with ADHD, the mutated gene and small amounts of lead exposure had more severe symptoms.

"These kids are more hyperactive and more impulsive," Nigg said. They'd be more likely to fidget in their seats or blurt something out in class and more likely to seem immature in their self control."

The gene does not cause ADHD, Nigg said. Children can have the mutated gene and not ADHD. A number of things have to go wrong, but this study shows that lead is one factor and that the effect depends in part on this gene, Nigg said.

He does not recommend that parents at this point in the research have children with ADHD tested for the gene mutation. He also said parents of children who are healthy and do not have ADHD should not worry about the gene unless there is a family history of lead poisoning.

But he advised parents with children with ADHD to get them tested for lead levels.

Eliminating all lead from the environment would require replacing old houses and school buildings.

"You'd have to spend a lot of money," Nigg said.

He said the study shows that eventually scientists will be able to identify children who are the most sensitive to lead exposure. It also offers hope that as scientists better understand ADHD, they'll have a better chance of preventing it in the future by identifying other environmental influences.

"The longer-term hope is that we will be able to prevent ADHD," Nigg said. "This is a piece of that picture."

-- Lynne Terry