I think I found the one that takes the cake...
I have a cousin who's family is... rather religious. When she was younger I'm pretty sure she was mostly normal. My older sister and her were close when they were teens and they hung out with friends, did normal teen stuff. Then when she was in her 20's, I'm not really sure, but I think she may have suffered some sort of traumatic experience. This is around the time she started to become super religious. Whenever I would visit them, she could hardly go more than 5 minutes talking about anything before she had to change the subject to God. She spent about 3-5 hours a DAY at church. One day she invited me to go to her church, which as a curious and open minded atheist, I had no problem with doing. You've heard of people speaking in tongues? She was doing that over 10 years ago. And not just in church (where they all started doing that at the end), but at home, even at the dinner table. Her parents would just roll their eyes at her whenever she did this like they thought she was just being silly.
They moved away for awhile and just recently moved back closer to where I can visit them again. When I saw her again for the first time in about 8 years, and I'm not kidding... but she looked like a female version of Hagrid. She gained about 100 lbs, she was dressed all in black and her long messy hair was covering her face. She wasn't speaking in tongues any longer. No, she's far being that point now. She not only changed her name to Faith, but claims to be a completely different person than she was the last time I saw her (pointing to old pictures of herself and saying "that person doesn't live here anymore). At the dinner table, one of her questions to me was "Do you believe in God???" I had no problem with answering truthfully. Her response, in her quiet shaky voice, "Well, I AM God". "ok, if you say so" I said and just smiled. Later on she asked me about atheists, "is it true that they eat babies???" "Umm, I'm pretty sure I've never eaten a baby..."
Sometimes in the middle of the night and I would hear her screaming at her parents accusing them that they were trying to kill her, saying that she knew about the times they would sneak into her room with a knife when she's asleep. Of course nothing like that ever happened. I think she has just slipped so far that she has lost all touch with reality.
To be fair, her parents finally recognize that there is something wrong with her and they are getting her help now. But the medication really only helps to alleviate the hallucinations. She still is incapable of working, hasn't had a job in over a decade. Doesn't do anything but stay in her room all day. Sometimes she leaves to eat or smoke. She's in her 40's now and I worry about what's going to happen to her when her parents are no longer able to take care of her. They're in their 70's.
They are extremely patient and good people. They've helped me out with a lot. They have always been religious and so have their other two older children, who both have normal families of their own. Only their youngest has taken it to such an extreme that she is not able to function. From my point of view, I can't help but think that their overacceptance of her religiosity is what led to her mind rotting as much as it has over the last half of her life.