Number of older siblings of individuals diagnosed with schizophrenia

One of the most consistent epidemiological findings in schizophrenia resear ch is the small excess of late winter/early spring births. There is also ev idence that schizophrenia is associated with urban birth and with later bir th order. One interpretation of these three findings is that respiratory vi ral infections brought into the household by children in crowded areas coul d disrupt foetal brain development and predispose to schizophrenia in later life. To further explore this hypothesis, case register data were used to assess if schizophrenics with a greater number of older siblings are more l ikely to be born in urban areas and during late winter/early spring months. Data from the Dublin and Three County Case Register were compiled relating to 2969 patients with schizophrenia and 5904 patients with neurosis. We us ed logistic regression analysis to determine if the number of older sibling s differentiated schizophrenia from neurosis after controlling for the effe cts of gender, urban/rural birth, season of birth and sibship size, and to examine whether any interactions existed. The number of older siblings did not predict a diagnosis of schizophrenia o ver neurosis. There was no interaction between number of older siblings and urban birth, between number of older siblings and spring birth, or between number of older siblings, season of birth and urban birth. These data do n ot support the hypothesis that schizophrenia, by comparison with neurosis, is associated with an increased number of older siblings or that there is a n interaction between number of older siblings, urban birth or season of bi rth. (C) 2001 Elsevier Science B.V. All rights reserved.