The classes run from one to five, one being the most severe and five being the least, based on how the protien is or isn't created, and what the problem is. Mutation is only one part of the Cf puzzle, but it can't be ignored either.
Ry was a W1282x , a type one, and a Deltaf508 , a type two.
People with 4 and 5 tend to have less digestive problems, or be pancreatic sufficient.