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October 02, 2004
Twins and Brain size
A controlled study of brain structure in monozygotic twins concordant and discordant for schizophrenia.
Technologies such as magnetic resonance imaging (MRI) allow researchers to take pictures of the brain. Such imaging studies have found that there are brain abnormalities in those suffering from schizophrenia. These include changes in volume of the brain, larger ventricles and decreases in sizes of certain structures (eg hippocampus and amygdala). Where do such brain changes come from? The environment or genes (characteristics you are born with that you get from your parents).
Studies done with twins who have schizophrenia suggest that both genes and environment play a role in such brain abnormalities. This current study looked at the effect of genetic vulnerability to develop schizophrenia and the role of genetic and environmental factors in any brain abnormalities found. Unlike previous MRI studies, this study was able to include a good sized sample of 82 participants that included monozygotic (identical twins, same egg) twin pairs where both had schizophrenia (concordant) as well as twins where only one had schizophrenia (discordant). They also included control twin pairs without schizophrenia and discordant same-gender siblings and pairs of unrelated control subjects.
They found that MRI brain scans showed that similarities in brain volume increased as pair members were more closely related genetically (monozygotic twins > siblings > unrelated control subjects). Twins with schizophrenia, whether from concordant or discordant pairs, had smaller whole brain volumes than control twins. Also, the person with schizophrenia in the discordant pair had more abnormalities in certain parts of the brain (eg hippocampus, third and lateral ventricles).
From this, the researchers concluded that brain size is affected by genetics and a smaller brain may be because of a genetic vulnerability to develop schizophrenia. However, the environment also seems to be involved, since there were twins who had identical genes yet the one with schizophrenia showed abnormal brain structures.
A limitation of this study is that the control twins were allowed to have other psychiatric conditions which can also affect the brain. Also, the researchers did not get information on the role of environmental events such as birth complications which could explain the difference in the brain volumes. They were also unable to get information on medications which could also have played a role. In the future, including healthy dizygotic (different eggs) twin pairs would also provide more information about the role of genes and environment in schizophrenia.
This research was sponsored by a travel grant (Neeltje van Haren) of the Netherlands Organization of Scientific Research (NWO: R56–465), Wellcome Trust, and Stanley Medical Research Institute.Posted by Farzin at October 2, 2004 12:05 AM | TrackBack