Lesson 1: Clinical Disorders – Part C
PART C
Suspected Causes (Etiology) of Schizophrenia
To date, no single cause of schizophrenia is known. It is believed by many health care professionals, that schizophrenia may result from a combination of genetic, behavioural, and other factors. Scientists do not yet understand all these factors, but with the advance of biomedical research, it is believed that several key genes that, when damaged, contribute to schizophrenia. Current estimations indicate that between 50 and 100 genes are involved in schizophrenia -- specifically those on chromosomes 6 and 13.
Research data confirms that schizophrenia runs in families. People who have a close relative with schizophrenia are more likely to develop the disorder than people who have no relatives with the illness. For instance, a monozygotic (identical) twin of a person with schizophrenia has the highest risk, 40 to 50 percent, of developing the illness. Please see Chart 6.1 for more information (Clarke, 2001).
Chart 6.1
Developing Schizophrenia and Relationship Links
| Relationship | Percent Likelihood of Developing Schizophrenia |
| Identical (monozygotic) twin |
40-50%
|
| Fraternal (dizygotic twin) twin |
12-15%
|
| Both parents have schizophrenia |
40-50%
|
| One parent has schizophrenia |
11-13%
|
| Sibling |
~ 10%
|
| Grandparent, aunt, or uncle |
~ 4%
|
| Niece or nephew |
~ 3%
|
|
No relation |
~ 1-2% |
In addition to genetic predisposition, factors such as prenatal difficulties (e.g., 
intrauterine starvation, viral infections, perinatal complications, various non-specific stressors) seem to influence the development of schizophrenia. One movie worth watching, A Beautiful Mind, is based on the true life story of John Nash, a Nobel Prize recipient who suffered from schizophrenia.
The following case study summarizes a well-documented report of four identical sisters (quadruplets) with schizophrenia. To protect the family’s privacy, in his report Dr. David Rosenthal used the pseudonyms Myra, Nora, Iris, and Hester for the sisters, Henry and Gertrude for the parents, and Genain for their last name. Dr. Rosenthal studied the quadruplets in detail at the National Institute for Mental Health. He has written a book, The Genain Quadruplets, New York: Basic Books, 1963 that provides much detail. A more recent review of psychological studies of these individuals may be found in the article by Mirsky et al, Psychiatric Research, September 1984.