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Interrelated Schizophrenic Psychoses in Fraternal Twins

Arch Gen Psychiatry. 1964;10(4):423-430. doi:10.1001/archpsyc.1964.01720220101016.
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The onset of psychoses in both identical twins, often with a striking similarity in symptomatology, time of onset, and severity of illness is an impressive phenomenon that has often been recorded as common,15,23,28 and occasionally described.3,11,19,29,30,31 We wish to report a similar occurrence in a set of fraternal twins who, despite differences in appearance, had been raised in a manner usual only among identical twins and who had continued to live syncytially until a few weeks before one became overtly psychotic at the age of 26.

Interest in schizophrenia in twins has until recently focused primarily upon the high concordance among identical twins in contrast to the lower concordance among fraternal twins and siblings. Luxenburger,20 Rosanoff,23 Essen-Moller,7 Kallmann,15 Slater,28 and others have documented such findings. Kallmann reported the most distinctive difference, a concordance of 86% in identical twins in comparison with


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