Is midnight snacking keeping you up late at night and keeping you off your diet? A faulty gene may be to blame, researchers said.

They found that mice with a mutation in a gene called "Clock" controlling circadian rhythms -- a member of a class of genes called clock genes -- develop symptoms similar to those seen in many overweight people, such as diabetes, high cholesterol and a tendency to gain weight.

Their findings, published in Friday's issue of the journal Science, suggests that a brain system that controls the cycles of sleep and waking may also help regulate appetite and metabolism.

Dr. Fred Turek and colleagues at Northwestern University in Illinois and the Howard Hughes Medical Institute found mice with a mutant version of the Clock gene tended to overeat, become overweight, and have high levels of blood glucose and cholesterol.

Their mutant mice were more active during times when rodents usually sleep. They had unusual levels of leptin and ghrelin, both hormones involved in appetite.

When fed a normal diet, they gained about as much weight as normal mice fed a high-fat diet. When they got fat-laden food, the mutant mice gained even more weight and showed metabolic irregularities.

"We don't know too much about how clocks control eating and metabolism in normal individuals, but now we have shown that weight gain and abnormalities in metabolism, including diabetes, result if this internal timepiece is malfunctioning," said Dr. Joseph Bass, an assistant professor of medicine and neurobiology at Northwestern.

"The body clock is clearly controlling the elaborate brain signaling system that regulates appetite."

Other studies involving leptin and appetite in mice have not translated directly to humans, but the researchers said the findings were always useful in understanding human disease and biology.

"Is it possible that sleep loss or a change in circadian rhythms might exacerbate problems in regulating appetite?" Bass asked.

"It may be a question of not only how much you eat but what time of day you eat and how that affects the body. Are you eating at a time of day when your system is internally aligned to metabolize the food?"