Since identical (“monozygotic”) twins have indistinguishable sets of DNA, they are frequently used as patients for a broad range of research.  Many studies surrounding schizophrenia aim to achieve a better understanding of the effects of the prenatal or external postnatal environment on the twins.

            Prenatal influences on unborn twins were the focus of one case study regarding schizophrenia (Davies, Phelps, 1995).  The researchers used handedness as a way to determine whether the subjects were developed within a single embryonic membrane (opposite-hand preference) or separately (same-hand preference).  Davies and Phelps found that opposite-handed siblings had the same diagnosis for schizophrenia 60% of the time while same-handed twins only had similar diagnoses 32% (1995).  Their findings suggested that a viral infection within the shared prenatal environment could possibly be responsible for the highly similar status of this disorder in twins (Davies, Phelps, 1995). 

In 2003, Kunugi et. al looked at twins with contrasting diagnoses for schizophrenia.  The unaffected newborn weighed 2300 grams while the affected twin was born weighing 1620 gram, signifying prenatal underdevelopment of just this one twin (Kunugi, Urushibara, Murray, 2003).  MRI testing results showed the smaller baby having high-intensity signals in his brain’s white matter and enlarged ventricles.  The unaffected twin did not have these abnormalities (Kunugi et al., 2003). During early childhood, there were considerable variations between the twins with respect to sociability and intelligence (Kunugi et al., 2003).  A similar study in 2005 showed same-sexed twins with a birth weight less than or equal to 1999 grams and a head circumference less than or equal to 31.5 cm had connections with a later development of the disorder (Nilsson, Stalberg, Lichtenstein, 2005).  These birth characteristics are a result of decreased development within the womb (Nilsson et. al, 2005) and are put forward as independent from genetic causes.

Recently, a group of researchers worked with twins to compare their memory abilities.  Within the twin pairs, one was affected by schizophrenia and the other was not.  Both children of the pair performed considerably below average in the verbal working memory tasks but only the affected twin achieved poor results in the spatial working memory tasks (Pirkola, Tuulio-Henriksson, Glahn, 2005).  Therefore, a reduced spatial memory function may highlight a genetic liability to schizophrenia (Pirkola et al., 2005).

These are just a few of the studies revealing possible causes or connections to schizophrenia in identical twins.  Hopefully, as we gain information regarding these aspects of the disorder, we will find treatment and prevention methods to assist all sufferers of this disorder.