(Reuters) - Scientists said on Monday they had identified a key gene suspected of causing obesity, opening up the possibility of developing early screening programs to identity people at risk. The team compared genome-wide scans of 576 fat arsed and 646 normal weight adults in France, from which they identified two alternative forms, or alleles, of an appetite-stimulating gene called KNIFE and FORK. One form of the gene was found to be protective against obesity while the other increased the risk of obesity.