Dear Dr. Beth,   Depression, alcoholism and other mental problems run in my family.  I have aunts, uncles, cousins and grandparents that suffer from various mental and substance abuse disorders.  Of course, not all of my family members suffer from these problems.  My question is this:  I want to get married and have children someday. I am really worried that one or more of my children will suffer from one of these illnesses and that makes me afraid to have children. How worried should I be?