I urge you to understand "cause" as a trigger. I know there is some genetic basis to depression, but this is usually triggered by events. For me, I believe because I've learned to keep my feelings inside me since my childhood. But I've become very depressed by outer events like social isolation and being ostracized and being in a different culture (cultural shock I guess).

I asked this question to follow it with another question which is: what do you think might help alleviate/reduce your depression symptoms?

For me right now finding a partner and job would probably make me feel better. I think I would still have the base tendency to be depressed, but at least I would have a reason or the motivation to not to surrender to depression. I am speculating, though, and might be wrong