Dysfunctional families do not necessarily have mental illness but they can certainly aggravate those individuals who do have a propensity toward mental illness. Families that have members with mental illness certainly are affected by that and it can cause them to be depressed but not necessarily cause the mental illness of MDD.

On the other hand trauma has a more likely chance of inducing MI in those predisposed towards it. What causes trauma in one person may not cause it in another. I believe it is a individual biochemical reaction. They are finding out that almost anything can cause a persons body chemistry to fluctuate, the food you eat, when & where you were born, environment, stress....again it is all individualized.