Fetal brain development of twins assessed in utero by ultrasound: implications for schizophrenia.

There is evidence that some forms of schizophrenia are due to alterations of in utero brain development. Given the concordance rate for schizophrenia in monozygotic twins is approx. 45%, it is not clear how a shared genetic predisposition for schizophrenia and a shared in utero environment might selectively lead to schizophrenia in one but not the other twin in a monozygotic twin pair. This study was undertaken to test the hypothesis that there is a difference in brain development between twins in a monozygotic twin pair that may contribute to the observed concordance rates for schizophrenia. Fetal ultrasound measures of brain (biparietal diameter, head circumference, ventricular width) and body size (femur length, abdominal circumference) obtained during the second trimester of fetal development were retrospectively analyzed in 41 monozygotic and 103 dizygotic twin pairs. In monozygotic twin pairs, there was a significant difference in measures of biparietal diameter, head circumference, and ventricular width, as well as in femur length and abdominal circumference, between twins. There was a similar difference in dizygotic twin pairs. These results indicate that in monozygotic twins, brain development is not identical. This difference in brain development may contribute to the observed concordance rates in monozygotic twins with schizophrenia.