Board Thread:Lore Discussion/@comment-5983727-20130112120518/@comment-3492791-20130123012241

It is stated during the Companion's questline that the strain they have is different than standard Lycanthropy, likely because it originates from the Glenmoral witches and not from Hircene.

SkyrimsLord13 wrote: Sinding's uncontrol was the result of him wearing Hircine's cursed ring

No. Sindling clearly states that he was unable to control his transformations before acquiring, or even knowing about the ring. He stole the ring because he had heard that it allowed one to control their transformations. Hircine didn't appreciate his artifacts being stolen and punished Sindling by making the ring do the exact opposite of its original intention, making transformations even more unpredictable.