Cellular degradation is a process in which cells become too unstable in an organism, resulting in its ultimate death. The clone of Carson Beckett, which Michael Kenmore created, suffered from cellular degradation. However, a sort of medicine was created by Michael to support the clone cells from deteriorating. Jennifer Keller was eventually able to replicate this treatment. (SGA: "The Kindred, Part 2", "The Seed")
The Asgard also suffered from cellular degradation, leading to their eventual demise. (SG1: "Unending")
However the Pegasus Asgard have been able to either slow down or temporarily repair their genetic damage. (SGA: "The Lost Tribe")