Both.

My brain chemistry is all kinds of messed up. So a big chunk of it is my genetics. Mental illness runs in my family; both of my parents suffer from depression and my sister is so bipolar they might as well create a new category of it for her.

But then also because my family needed someone with emotional strength, I pretty much became the "rock". I created a "false self" that was always helping, being the emotional support for others and ignoring my own feelings.

Combining my own brain chemistry problems with the "false self" and bingo! Major Depressive Disorder. Joy!