There is a long lsit of culture , palces, etcc where depression is non-existent... so we know depresion is purely a social factor.. that indeed changes your body adn the level of neurotransmittor...

On the other hand schizofrenia is considered to be universal.. there are records of peole behaving as such in a lot of different places...but in this case the general thinking is that it is a problem of brain functioning.. this means that the origin could be pure DNA or more probably some problem in the DNA-protein network or even some interaction with the envronment at an early stage that can produce this illness (or a bad DNA-protein circuit) very easily...

And regarding the bi-polar deficient disorder I just love your comment.

A pleasure

I therefore claim to show, not how men think in myths, but how myths operate in men's minds without their being aware of the fact. Levi-Strauss, Claude