My god! Worf's trip back in time might have infected the Klingons on K-7!!! Perhaps that is what started the change! That in one timeline, it was created by Klingon geneticists, but when Worf went back in time to K-7 and carried the disease that started the change, he himself caused it! That is why Klingon science was unable to find a cure... they were looking in all the wrong places!
I can just imagine Klingon doctors and scientists trying to find out the cause of infection... checking Tribbles, quadrotriticale, humans... of course Worf was long gone back to the future. If the plague of forehead-wrinkling had occurred around the geneticists, they would have had a clue about what was going on and had a fair chance if stopping it. This would also explain the popular fan theory that the Tribbles were the cause of the klingon forehead-wrinkling. They weren't, but the Klingon doctors THOUGHT they were...