BC, I used to work in psychiatry, with young chronic schizophrenics.
I recall reading years ago of a multi-centre study done on
schizophrenia rates.  As I recall it, they agreed on a set of
definative hard symptoms (eg hallucinations plus others) and then
measured them in a number of countries that did include developing
countries and was not just western cultures. (That's why I remember
the study because I was fascinated on how they identified the
syptoms in such diverse cultures.)  The symptoms were apparent at
about the same rate in all the cultures, although how these people
fitted into their cultures varied considerably (eg many of the so
called "village idiots" and "weirdos" may have been schizophrenics
supported and well tolerated in the local community).

There are degrees of schizophrenia, ranging from chronic to a single
psychotic episode. There is good evidence for a biochemical basis
and a genetic factor, possibly an inherited pre-disposition.  Unlike
other genetic conditions (such as Downs sydrome which Kathy D
mentioned), schizophrenia does not manifest until late teens/early
adulthood and is not necessarily a threat to survival.

I remain skeptical about infant formula as a cause. Particularly when
the blame is narrowed down to a single ingredient that can now be
manufactured commercially and added to formula.  I am suspicious.

Ros Escott BAppSc IBCLC
Tasmania, Australia