Obese children whose overeating is nearly uncontrollable may be missing portions of DNA, a British study suggests.

Researchers from the University of Cambridge took DNA samples from 300 children who tipped the scales at 220 pounds by age 10 and compared their genomes to more than 7,000 healthy volunteers.

In rare cases, the children were missing part of chromosome 16, which normally tells the brain to stop eating in response to the hormone leptin, which controls appetite, the team reported in Sunday's online issue of the journal Nature.

Children with the chromosome 16 deletion were "very, very hungry," said Dr. Sadaf Farooqi of Cambridge, one of the study leaders. "They always want to eat."

Child abuse blamed at first

The findings suggest a particular gene on chromosome 16, called SH2B1, plays a key role in regulating weight and handling blood-sugar levels, Farooqi said.

So far, the findings have already helped in the cases of four children with the deletion. British child welfare authorities had blamed their parents for deliberately overfeeding them.

Researchers were able to intervene in two of the cases misattributed to abuse, and the other two are under discussion, Farooqi said.

The mutation likely affects fewer than one per cent of children, the researchers estimated.

It's the first evidence that mutations known as copy number variants — large chunks of DNA that are duplicated or deleted — may be linked to obesity, said Matt Hurles of the Wellcome Trust Sanger Institute, who also led the study.

Such mutations have also been shown to cause disorders such as autism.

The work offers "a gold mine of information" for scientists looking for obesity-related genes, said Eric Ravussin, an obesity expert at the Pennington Biomedical Research Center in Baton Rouge, La., who wasn't involved in the study.