To what degree does environment govern the severity of symptoms in schizophrenia?
I think reading about the genain quadruplets should give you a clear idea of the effect of environment on schizophrenia. Basically, the quadruplets had a genetic disposition to this disorder and all 4 siblings were admitted at some point or another to the National Institute of Mental Health as schizophrenic. However, there were differences in the severity of the disorder in all 4 siblings due to the way they were treated by their parents, showing that despite genetic dispositions to a disorder, environmental factors do affect the severity of it.