How similar are the brains of twins? I am currently reading undergraduate essays on biological dysfunction and schizophrenia. The students put a lot of weight in the fact that studies of monozygotic twins show only a 50% rate of concordance. How similar, in terms of anatomical structure and connectivity, are the brains of monozygotic twins?
Biondi et al. (1998) compared MR images of monozygotic twins and found that while the brains of monozygotic twins are not identical, they are similar. Relevant for understanding the concordance rate of schizophrenia in  monozygotic twins, Suddath et al. (1990) examined MR images of monozygotic twins who where discordant for schizophrenia. They found that the schizophrenic twin had enlarge cerebral ventricles and subtle anatomical abnormalities although the study seems to lack a control group of either both schizophrenic, both normal, or discordant on some other disease.