Researchers have discovered genes linking a person's circadian clock with their eating schedule, according to a recent study.

The urge to eat a meal or snack typically comes at a few, predictable times during the waking part of the day. But for those with a rare syndrome, hunger comes at unwanted hours, interrupts sleep and causes overeating.

Scientists from the Salk Institute for Biological Studies have discovered a pair of genes that normally keeps eating schedules in sync with daily sleep rhythms, and, when mutated, may play a role in so-called night eating syndrome. They found that in mice with mutations in one of the genes, eating patterns are shifted, leading to unusual mealtimes and weight gain.

"We really never expected that we would be able to decouple the sleep-wake cycle and the eating cycle, especially with a simple mutation," Satchidananda Panda, senior study author and an associate professor in Salk's Regulatory Biology Laboratory, said in a statement. "It opens up a whole lot of future questions about how these cycles are regulated."

For the study, Salk scientists joined forces with a Chinese team led by Ying Xu of Nanjing University to test whether mutations in the equivalent area of PER1 would have the same effect as those in PER2 that caused the sleep disorder.

They bred mice to lack the mouse period genes, and added in a human PER1 or PER2 with a mutation in the phosphorylation site. As expected, mice with a mutated PER2 had sleep defects, dozing off earlier than usual. The same wasn't true for PER1 mutations though.

"In the mice without PER1, there was no obvious defect in their sleep-wake cycles," Panda said. "Instead, when we looked at their metabolism, we suddenly saw drastic changes."

Mice with the PER1 phosphorylation defects ate earlier than other mice -- causing them to wake up and snack before their sleep cycle was over -- and ate more food throughout their normal waking period. 

"For a long time, people discounted night eating syndrome as not real," Panda said. "These results in mice suggest that it could actually be a genetic basis for the syndrome."

The researchers haven't yet tested, however, whether any humans with night eating syndrome have mutations in PER1.

The findings were recently published in the journal Cell Reports.