Quote Originally Posted by Rpgirl_yuna
I have read articles saying that they are are from the EXACT same experiment Seph was in. But with one minor change they are the ones that started the geostigma THEY control hence the scene in the trailer that has Kadaj talking to the kids and Denzel with normal eyes and then it snaps to a photo of him with the Geostigma.
[spoilers]They didn't start Geostigma, nor can they control it. Geostigma is the side effects of an inner conflict between JENOVA's Cells and one's Spirit Energy as the two fight for dominance of the body. The battle produces too much strain for a body to take, however, causing extreme fatigue, sores, and open wounds.[/spoilers]