Structural brain abnormalities have consistently been found in people with schizophrenia and can get worse as the disease progresses. More pronounced changes in brain volume are linked to worse outcomes but cause and effect in this relationship are unclear and there is the added complication of medication use which may also affect brain volume. Studies of twins, both identical and non-identical can shed light on the role played by genetics in schizophrenia. A Dutch study with 92 participants looked at 9 pairs of identical twins and 10 pairs of non-identical twins where one twin had schizophrenia and the other didn't. The results were compared with 14 pairs of identical and 13 pairs of non-identical twins none of whom had schizophrenia. In the pairs of twins where one twin had schizophrenia even the unaffected twin (the co-twin) showed a significant decrease over time in whole brain and frontal and temporal lobe volumes. At least 51% of the correlation between brain-volume loss and schizophrenia could be explained by genetic factors that are also directly implicated in the disease. None of the co-twins were taking anti-psychotic medication so this could not have been to blame for the loss of brain volume.
Brans, Rachel G. H. ... [et al] - Heritability of changes in brain volume over time in twin pairs discordant for schizophrenia Archives of General Psychiatry November 2008, 65(11), 1259-1268