what is the genesis of mental illness?

[reeay]

Usually you look at
biological predisposition + environmental factors (nature/nurture)

But for childhood disorders (e.g., autism) you may look at
biological predispositions + environmental factors + gestational/maternal health + exposure to toxicity in environment

There is no real understanding of what 'causes' mental illness, as there are just too many variables that impact a person's social, biological, and psychological health. Psychology is a very divided field with people from many different schools of thought. Depending upon what theoretical framework you work with, the explanation of causality may differ. The psychiatric (medical model) is just one school of thought that seems to dominate the field, unfortunately.