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Recent reports that some influenza epidemics may be followed by a transient increase in the births of schizophrenic patients have led to the hypothesis that maternal viral infections contribute to the aetiology of schizophrenia. It is well known that respiratory viral infections are frequently brought into the home by young children. We tested the predictions that the risk of schizophrenia is decreased in first-born children, and increased in individuals who had siblings of a young age while in utero, using data from a Swedish family study. Our results are consistent with these predictions. In particular, having siblings three to four years older was associated with a significantly increased risk of schizophrenia, even after allowing for birth order, sibship size, and other potential confounders. If replicated, these results provide indirect support for the maternal viral infection hypothesis, although there are alternative explanations. [ABSTRACT FROM AUTHOR]

Background: To understand the relationship between parenting and psychopathology in offspring, it is critical to clarify the determinants of parenting behaviour itself., Methods: A 16-item version of the Parental Bonding Instrument (PBI) was administered to parents of epidemiologically sampled adult female-female twin pairs, who reported on the parenting they provided to their twins, and to the twins themselves who reported on the parenting they and their co-twin had received (N = 828 twin families). Using a mixed-model regression, we examined the impact on parenting, as retrospectively reported by parents and twins, of six variable domains: demographic factors, family characteristics, parental symptoms and personality, parental psychopathology, child vulnerability and childhood temperament., Results: The PBI yielded three factors: warmth (W), protectiveness (P) and authoritarianism (A). W was most strongly predicted by parental personality and psychopathology, parental marital quality, and child temperament. P and A were both most strongly predicted by parental educational level and religious fundamentalism. In addition, P was predicted by neurotic/anxious traits in both parent and child. For a number of variables that predicted W, the strength of the association was stronger when twins were reporting than when parents were reporting., Conclusions: Parenting is a complex, multi-determined set of behaviours that is influenced by parental personality, psychopathology, values and marital quality and by a range of child characteristics. W appears to be strongly influenced by parental and childhood temperament and vulnerability to psychiatric illness while P and A are more strongly influenced by 'sociological' factors such as religious affiliation and educational status.