'Sumo' rats at the National Institute of Nutrition in Hyderabad are the focus of a new joint project for scientists from India and the US.

The rats, believed to contain hitherto undiscovered obesity genes, weigh as much as 1.4 kg -- about four times the normal size.

The Indo-US study hopes to identify those genes that make the 'sumo' rat extraordinarily fat, says a report in Nature Medicine.

External link: Nature Medicine

The work on isolating and cloning the novel obesity gene will be done partly at NIN and partly by US collaborators led by Jeffrey Friedman at Rockefeller University in New York.

"If, as we believe, this is a new obesity gene, it could have major implications," says Nappan Veettil Giridharan, deputy director of NIN, the key scientist responsible for developing the 'sumo' rats.

The NIN maintains a colony of about 400 'sumo' rats. Like other rodent models, the 'sumo' rats serve as good paradigms for human disorders such as diabetes and infertility.

These rats also develop cataracts and tumors and their infertility is fully reversible by diet restriction. The rats have kinky tails, not seen in any other obese models.