When Dr. Sadaf Farooqi and colleagues discovered a genetic abnormality that caused severe obesity in a handful of children, she had no cure. Yet the scientist transformed four families' lives nonetheless.

The British parents had been living in fear of losing their children — the youngsters' severe obesity had been seen as a possible sign of abuse or neglect, and they had been put on the list of the country's social services department.

"They were being blamed for their children's condition," Farooqi said.

Farooqi told authorities that this abnormality — a DNA deletion — wiped out a key gene involved in the body's response to leptin, a hormone that controls appetite. The children were taken off the list.

Farooqi's study, published last month in Nature, affected only five of about 1,200 severely obese youngsters. But as more genes related to obesity are unearthed, and as rates of childhood obesity climb, courts, social services and parents increasingly will have to grapple with difficult social and legal questions:

Can extreme childhood obesity be considered abuse? How much of a child's weight can be blamed on the parents, and how much is out of their control?

A three-decade rise in childhood obesity rates has meant that related abuse and neglect cases are more often making their way into the courts. According to a 2008 report by the Child Welfare League of America, "California, Indiana, New Mexico, New York, Pennsylvania, and Texas have had to determine whether morbidly obese children whose parents are unable or unwilling to control their children's weight against medical orders are properly considered abused or neglected."

In 2007, North Carolina mother Joyce Painter was told she would lose her 255-pound, 7-year-old son if he did not show progress in his weight loss within two months.

And in June, South Carolina mother Jerri Gray lost custody of her son Alexander Draper after being charged with criminal neglect. The 14-year-old weighed 555 pounds. Gray is facing 15 years on two felony counts, the first U.S. felony case involving childhood obesity, said her lawyer, Grant Varner.

Such cases will require authorities to consider not only genetics but the helplessness parents can face in trying to regulate a child's behavior, especially that of a teen.

So far, genetic tests have played a limited role in cases of childhood obesity in which authorities have become involved (Draper has not been tested, Varner says). The tests are fairly new, expensive and assess only a few of the genes known so far to strongly influence obesity.

In any case, for all but a small number of people, genes tell only part of the obesity story.

"What genetics does is sort of set the range of weights for you," said James O. Hill, director of the Center for Human Nutrition at the University of Colorado in Denver. "If you're somebody who is genetically predisposed ... you may never be lean, but there's still a wide range of weights in there."

But today's environment is likely to push many kids to the higher end of their range, said Dr. Marc Jacobson, who sits on the American Academy of Pediatrics' obesity leadership work group. In 1955, he said, McDonald's fries were 210 calories, but the large portions more often consumed today are 500. A Coke was 6.5 ounces, versus 20 ounces in today's plastic bottles. No wonder, he said, that today U.S. kids have an obesity rate of 15 percent, and that another 15 percent are overweight.

"Food is available 24/7. Domino's delivers. We're not programmed for that kind of environment," Jacobson said. "We're programmed for an environment where food is scarce."

Some of the factors are hard for parents to control, especially if they live in disadvantaged communities, said ethicist Erika Blacksher, a research fellow at the Hastings Center.

"It's unfair to hold parents accountable for factors such as whether their neighborhoods have safe places for their children to play ... or when their neighborhoods don't have grocery stores that sell healthy foods," she said.