Describe and evaluate the possible factors to schizophrenia

The corresponding rate in DZ twins is only 10%, which is about the same as for siblings generally. All studies consistently reported concordance rates, which are higher for MZs than DZs.
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             Although twin studies provide strong evidence for the operation of genetic mechanisms, they also indicate that other, non-genetic, factors must be important. If schizophrenia were a wholly genetic disorder, we could expect a concordance rate of 100% in MZ pairs in whom one twin was already affected. But, as we have seen, the real rate is less than 50%, which indicates that additional factors must be involved, either to increase the vulnerability of the affected twin or to protect, in some way, the healthy twin.
             Some researchers claim to have found evidence for specific genes seem to be associated with schizophrenia. One example is the study by Sherrington et al (1988) which provided evidence of a link between schizophrenia and a gene located on chromosome 5. Unfortunately, other researchers have not been able to replicate the finding, suggesting that Sherrington's observations were either a false positive result, or were limited to the particular families in his study.
             Studies using the techniques of CT and MRI have shown that, in comparison with "normal" people, those with schizophrenia have smaller brains and larger cerebral ventricles. The differences are small, but have been found in many studies (Brown et al 1986). Post-mortem studies (Woodruff et al 1997) have also revealed evidence of subtle disturbances in the structure and organisation of brain cells, particularly in the regions of the temporal and frontal lobes.
             Structural abnormalities have been found more often in those with chronic symptoms, rather than acute symptoms of schizophrenia, lending support to the belief that there are two types of schizophrenia. However, the fact that many people with acute symptoms of schizophrenia later go on to develop chronic symptoms, which could indicate further degeneration of the brain rather than two distinct types of schizophrenia.