Molecular geneticist Shiva Singh, from The University of Western Ontario, has been working with psychiatrist Richard O'Reilly to determine the genetic sequencing of schizophrenia using identical or monozygotic twins.
Singh looked at about one million markers of identical twins (and their two parents) where only one twin had schizophrenia.
"The most informative feature of schizophrenia is that it sometimes runs in the family," says Singh, noting in the general population about one percent have schizophrenia.
"We started with the belief that monozygotic twins are genetically identical, so if one member of identical twins has schizophrenia, then the risk for the other twin should be 100 percent, if it's all due to genes. However, studies over the years have shown that the risk of the disease in both twins is only 50 percent." That means either the twins are genetically not identical or the familial disease involves non-genetic (random) effects.
Singh found about 12 per cent of DNA can vary across individuals, "Cells are dividing as we develop and differentiate. More importantly, these cells may lose or acquire additional DNA. The genome is not static," he added.
The study is published in this month's PLoS ONE.