Family pedigree studies demonstrate that the risk of developing schizophrenia increases the more closely one is related to someone who already has the illness. For instance, first-degree relatives have a 10% risk whereas for first cousins the risk is reduced to 3%. (Kendler et al 1994)

However, this study can be criticised because it fails to take into account of the shared environment: after all, closely related people tend to live together. However, were genetic mechanisms not involved, it is hard to see why cousins, aunties and uncles should have a 3-fold greater risk, when they usually live away from the person with schizophrenia. Therefore, in general, pedigree studies have provided supportive, but not conclusive, evidence for the role of genetic factors.

A second approach to understanding the contribution of genetic mechanisms is by looking at adoption studies. If there were no genetic factors involved, then we would expect that the risk of developing schizophrenia would be much less in those children adopted away than the children continuing to live with their affected parent(s). In fact, Rosenthal (197

1) have shown that there is the same risk to children who have been adopted away from the affected parent, which provides strong evidence for the operation of a genetic mechanism.

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.

Furthermore, there have also been studies of the children of healthy people who were adopted by parents who themselves had schizophrenia (e.g. Wender et al, 1974). If genetic factors were important then we would predict that adoption by ill parents should not increase the risk. Wender’s results support this notion, indicating that growing up in proximity to a person with schizophrenia is not in itself a significant risk fa

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