The relationship of twinning to the familial-sporadic distinction in schizophrenia.

Cerebral ventricular enlargement in schizophrenia may occur more often in the absence of a family history of the disorder, suggesting that it is related to some non-genetic component of aetiology. This paper shows the finding to be much more apparent in a group of twins than in a similar group of singletons. Previous studies have shown twins in general to have larger cerebral ventricles than non-twins; we suggest that it is the greater susceptibility of twins to obstetric complications that is responsible for both the larger cerebral ventricles found in normal twins, and the very marked increase in ventricular size found in family history negative schizophrenic twins. We go on to consider evidence relating to a possible increased susceptibility of twins to develop schizophrenia.