It does seem to run in some families, but many genes and circumstances may be involved and it can be very different for different people. In my own family, I could trace one line of my Mother's side back to the late 1700s and there were suicides in every single generation. Men over age 50, women under 30. Amazing when I was able to see that on paper in black and white. It explained a lot! The interesting thing is that this is the family line that seems to have autism too, although that is difficult to document. Many of the suicides may have been due to struggles with autism,
Yes, science has proven there is a likely link to depression in many families. We are still very early in the stages of learning about autism, depression, and understanding the physical/neurological/developmental, and biochemical basis for many diagnoses. Interesting, isn't it?