NEW YORK - Some children get severely obese because they lack particular chunks of DNA, which kicks their hunger into overdrive, researchers report.

The British researchers checked the DNA of 300 children who'd become very fat, on the order of 220 pounds by age 10. They looked for deletions or extra copies of DNA segments.

They found evidence that several rare deletions may promote obesity, including one kind they studied further and found in less than 1 percent of about 1,200 severely obese children.

That deletion, on chromosome 16, apparently causes trouble because it removes a gene that the brain needs to respond to the appetite-controlling hormone leptin, said Dr. Sadaf Farooqi of Cambridge University.

In her study, children with a chromosome 16 DNA deletion "have a very strong drive to eat," said Farooqi, who co-led the research. "They're very, very hungry; they always want to eat."

The work, reported online yesterday by the journal Nature, already has produced a real-world payoff. Farooqi said that four children with the chromosome 16 deletion had drawn the attention of British child-welfare authorities, who blamed the parents for overfeeding them.

"We were able to intervene" and get the parents of two children off the hook, and the other two cases are under discussion, she said.