Disclaimer: I'm no expert in any of this, but I've listened to podcasts about such things by other people ;), and I don't care enough to battle with citations.
With that out of the way, from what I understand even genetic conditions like mental illness are often expressed due to environment.
I know that I'm likely on the ADHD spectrum and that I have a natural level of anxiety. I also know that as a JW those things were nearly crippling. I always had suicidal ideations as well. Since disassociating, no more ideations, not a one, my social anxiety is down to a dull roar and I've gone into lots of new situations, and I focus much better. I did things to work on all of that prior to disassociating, but it practically went away afterward.
BPD isn't actually something that is diagnosed in much of the population anyway, but I think that in general JWs do bring out mental illness in various ways.