I hink there is not a term for such situation. comorbidity is the condition that one person has more than one psychological disorder diagnosis. It might cover the condition but as far as I know, it doesn't talk about the relationship between more than one disorder. There might be many reasons for comorbidity, two disorders can as you said, lead to each other or have similar byological dispositions. most of people with psychological disorders have more than one diagnosis. There are many discussions about comorbidity and it's implications on effectiveness of our diagnostic tools. for reference, I found this article by Kendall and Clarkin(1992):
Kendall, P. C., & Clarkin, J. F. (1992). Introduction to special section: Comorbidity and treatment implications. Journal of Consulting and Clinical Psychology, 60(6), 833.
If you are talking about interacting with someone with a disorder, some behaviours such as violence by a person with a disorder can lead to PTSD but although I don't know it for sure, it won't be different from any PTSD?