There is a hereditary component. All the women on my mother's side of the family have/had different forms of depression, although none will admit to it. I had never shared with my mother what was going on with me until 8 years after I was diagnosed. It wasn't that I was denying it, I just didn't have any relationship with my mother.
My psychiatrist talked me into telling her and when I did, with my psychiatrist, I mentioned it was hereditary. My mother's response was classic mom... "you didn't get that from me. My mother and sister are bipolar, but I'm fine." Yeah, right.