Fat Gene Found

Scientists have discovered a gene in mice that appears to make them fat when it malfunctions. They have also found a similar gene in humans.

Scientists have long known that the tendency to be fat, or obese, is caused at least in part by genes people inherit from their parents. Breeding experiments with mice have indicated that at least five different genes likely play a role in weight regulation and diet.

Researchers led by Jeffrey M. Friedman at Rockefeller University in New York City looked for one of those genes by studying a strain of mice that eat so much that they can grow five times as heavy as normal mice. The researchers compared the genetic material DNA in the fat mice to the DNA in normal mice. They found one gene that was consistently mutated, or altered, in fat mice but never in normal mice. They named the gene "ob", short for obese. The normal gene is active only in fat cells where it produces a protein similar to other hormones that circulate in the blood. The mutated gene in the fat mice fails to produce the protein. The researchers published their findings in the December 1, 1994, issue of Nature.

Scientists believe the protein travels from fat cells through the bloodstream to the brain. In the brain it suppresses appetite and increases metabolism, the rate at which the body burns fuel. When enough fat cells produce enough of the protein, a mouse feels satisfied and does not eat any more. But when the gene is mutated and produces either no protein or a faulty version of it, the brain never gets the "satisfied" message, and the mouse continues to eat more than it needs.

Once the researchers isolated the gene in mice, they searched for a similar gene in humans. They found a section of DNA on chromosome 7 in humans that closely resembles the ob gene in mice. They have not yet shown that this gene plays any role in weight control or if it is mutated in fat humans. According to the Washington Post, Friedman is conducting experiments that could provide that information in the future.

Scientists believe that the discovery of the ob gene could one day lead to treatments for obesity. If they could develop a drug that would mimic the action of the healthy gene, fat people might be able to take it to dampen their appetite and increase their metabolism. But the researchers emphasized that any such drug is many years away. Also, genetics is clearly not the only cause of obesity in humans. The Rockefeller researchers said other research has indicated that genes account for anywhere from 60% to 90% of obesity. But genetics cannot explain why the number of people in the United States who are more than 20% over their ideal weight has increased from 25% of the population to almost 35% in the past 10 years. It is commonly recognized that people overeat for a variety of reasons, including relief from boredom, stress and unhappiness. For now, diet and exercise are the only proven ways to control weight.

Sources

"Born to Be Fat: Will an Obesity Gene Tilt the Scales Toward Social Acceptance?" Rick Weiss. Washington Post Health, December 6, 1994, page 10.

"Research Links Obesity in Humans to Flaw in a Gene." Natalie Angier. New York Times, December 1, 1994, page A1.

"Researchers Find Gene in Mice That Controls Fat." John Schwartz. Washington Post, December 1, 1994, page A1.