@suntan12- I was always under the impression that schizophrenia was hereditary, as well. In my psychology class, we studied mental disorders at great length. The way that I understand it is that we may have a biological predisposition to the disease but it is not necessarily hereditary.
Another way to look at it is to compare it to substance abuse. Someone might be born with a predisposition to substance abuse or have that “addictive gene”. They may go their whole lives without drinking or doing drugs. However, they might try alcohol one time and then develop an addiction for it. They have ignited that gene.
Other studies have shown that mental disorders do run in families but that the severity may not be the same. Meaning, a parent might have severe schizophrenia with psychotic episodes and the child may just suffer from depression or anxiety.