Research has shown that schizophrenia is heredity and can runs in families. This suggests that genes play a significant role. The closer the genetic relationship the more likely the people are to share the disorder. Evidence from family studies by Gottesman showed that when bothparent are schizophrenic then there is a 46% chance of the child getting it, however, if only one parent had it, it dropped to 17%. This suggests that a genetic factor is involved.
MZ twins share 100% of their genes; DZ twins share 50% of their genes. If genes are a factor we would expect more identical twins to share the disorder than non-identical. Gottesman also looked at twin studies, he found that that the average concordance rate for monozygotic twins is 46% whereas is it only 14% in dizygotic twins. This was because MZ twins were more similar in their genetics. These results were also supported by a study by Cardno et al which used strict diagnostic criteria they showed concordance rate of 26.5% for MZ twins, but only 0% for DZ twins. This provides strong evidence for a genetic component.
However there are many issues with this kind of research MZ twins are very rare and of these only 1% would be expected to have schizophrenia, so sample size in these studies are usually small, because only a select number of families are used these studies would lack population validity, there would be issues with the findings as they will be generalised to the whole population but they are only based on a few people. Another issue when looking at twin studies is that it’s very difficult to separate the influence of nature v nurture, the fact that concordance rates are not 100% suggests schizophrenia cannot be explained by genes alone, it may that an individual has a pre-disposition to this disorder that simply makes them more vulnerable to schizophrenia. This suggests the genetic account cannot give a full explanation