Gene studies are getting closer to finding gene markers, and research is ongoing. According to one therapist who stays up on the scientific literature, chances are strong that if you have bipolar disorder there will have been someone in the past 5 generations statistically who also had a mood disorder (not necessarily bipolar). The problem is that few of us have that much family information, and older generations generally weren't diagnosed because that just wasn't done.

I'm the first person in my family to be diagnosed, but there are some odd stories about my grandmother that could perhaps point that direction, but there is no way to really know.