Degeneration

Noun

1. The process or state of growing worse, or the state of having become worse.
2. That condition of a tissue or an organ in which its vitality has become either diminished or perverted; a substitution of a lower for a higher form of structure.

   "fatty degeneration of the liver"

3. Gradual deterioration, from natural causes, of any class of animals or plants or any particular organ or organs; hereditary degradation of type.
4. A thing that has degenerated.