Are MDD and Our Genes Linked?

What kind of influence do genes have on occurrences of major depressive disorder (MDD)?  How do we figure out the links and how do we adapt our treatments to best help patients?

First, we have to acknowledge the base question that this, and many other investigations into the causes of mental health issues, comes down to: Nature versus nurture.  Biology versus environment.  Hardwired—or acquired?  What about both?

Environmental Factors

It is strongly believed that environment plays a large part in mental development, particularly in childhood.  A negative environment