I would say you can write a story revolving around a disorder you don’t have, so long as you talk to, or read the account of, one person or multiple people who have that disorder, so you understand the ways people react to it. I wrote a short story revolving around a character in high school suffering from schizophrenia, but I made sure to listen to Ted Talks about it, and read up on it, I even did a research paper on it, before I wrote that story.