However, it is clear that bad parenting or a dysfunctional family is not one of the factors to develop schizophrenia. "Schizophrenia is caused by a genetic vulnerability coupled with environmental and psychosocial stressors, the so-called diathesis-stress model(http://www.schizophrenia.com/research/surg.general.2002.htm)". Complications prior to birth, or after birth, contribute to the likelihood of getting schizophrenia. Also, the underclass is more prone to developing schizophrenia than the upperclass, because the underclass is associated with more stresses.
"The twin studies showed that if one identical twin has schizophrenia, then there is a 30-50% chance that the other twin will have it as well. If a fraternal twin has schizophrenia, then there is a 15% chance that the other twin will have it as well. (This is the same percentage as any brother and sister)(http://www.thetech.org/genetics/ask.php?id=112)".
In closing, the book, Divided Minds: Twin Sisters and Their Journey Through Schizophrenia, by Pamela Spiro Wagner and Carolyn S. Spiro, M.D., give an account of what it is like to be twins where one suffers from schizophrenia and the other does not. "Told in the alternating voices of the sisters, Divided Minds is a heartbreaking account of the far reaches of madness as well as the depths of ambivalence and love between twins. It is a true and unusually frank story of identical twins with very different identities and wildly different experiences of the world around them. It is one of the most compelling histories of two such siblings in the canon of writing on mental illness" (http://books.google.com/books?id=C347R0goaa0C&dq=divided+minds:+twin+sisters'+journey+through+schizophrenia&source=gbs_summary_s&cad=0).