by the way...

research into the genetic basis of mental disorders is highly problematic for a number of reasons...

firstly... inter-rater reliability is poor. that means that if you video-taped a person and asked clinicians to assess what mental disorder they had then there would be a GREAT DEAL of disagreement by the clinicians as to what disorder the person had.

the genetic research into the basis of schizophrenia relies on the people being diagnosed with it actually having it and the people who aren't diagnosed with it actually not having it.

the place to start with the genetic research is with linkage analysis. basically... take a family tree and look at the individuals on the family tree that are affected with the condition. this allows you to say whether it has a dominant genetic basis or a recessive genetic basis or whatever. basically... linkage analysis reveals that the genetic basis for schizophrenia isn't anywhere near as simple as that.

so people posit some complicated combinations of genes (where by genes now what is meant is values on a particular location of the chromosome).

probably the best study that has been done is the stuff that has focused on analyzing data from the icelandic genome project. how come? because they have kept extensive health records for every member of the population including diagnoses and... their genome.

so... great data to try and find the genetic basis.

the BEST candidate for the genetic basis of schizophrenia that emerged from that project was 3 particular values (in a certain combination) on 3 distinct places on the genome. sometimes 'genetic' is used to mean that (rather than mere location). so... what are the chances? About 15 percent of people without schizophrenia have those 3 values in that combination on those three places on their genome. About 7% of people with schizophrenia had those 3 values in that combination on those three places on their genome.

We need to remember the diagnosing bias in that you are much more likely to be diagnosed with schizophrenia if you have a family history because firstly, you are more likely to come to medical attention in virtue of your family history and because secondly, clinicians are more likely to diagnose you with schizophrenia if you have a family history BECAUSE CLINICIANS ANTECEDENTLY BELIVE THAT SCHIZOPHRENIA IS HERITABLE. If you had the same person present with the same symptoms and the clinician was told that bi-polar rather than schizophrenia was in your family history THEY WOULD MORE LIKELY DIAGNOSE YOU WITH BI-POLAR.

Another problem... The genetic basis of the icelandic population is very homogenious (read in-bred). That means that they aren't at all a representative genetic sample of human beings in general, and that means that it is highly questionable that those three values on those three loci have ANYTHING AT ALL TO DO WITH SCHIZOHPRENIA IN OTHER POPULATIONS. And remember... That even with that homogenious genetic sample of the population the correlation between those three values on those three gene loci were BARELY SIGNIFICANT.

And that... Seems to be about the best we can do.
I have to say that I have no faith whatsoever in their being any better genetic basis to be found.