Winter births have been repeatedly shown to produce an excess of later-diagnosed schizophrenics. Viral infections, in view of their seasonality, have been prominent among the proposed explanations of the winter birth findings. As part of a larger project, we proposed to follow-up a Helsinki cohort of 6,097 consecutive deliveries which occurred during the 1957 type-A2 influenza epidemic. These individuals, 27 years of age at the time of the search, would be followed-up in the Finnish Psychiatric Registers for any evidence of mental illness, including schizophrenia. It was hypothesized that those whose mothers suffered a perinatal influenza infection would evidence an elevated risk of schizophrenia as compared to those whose mothers were free of an infection. In addition, it was hypothesized that among those who experienced an influenza infections, the schizophrenia diagnoses would be concentrated among those who were genetically predisposed among those with a parental schizophrenia diagnosis. It is the specific aim of this proposal to undertake a pilot study to determine the feasibility of pursuing the larger study proposed above. The pilot study will test the hypothesis that systematic examination of the records of Helsinki mental hospitals will reveal an unusual bulge of cases of schizophrenia among those born at or near the time of the 1957 type-A2 influenza epidemic. No study to date has directly examined, in a large population, the possible effects of a perinatal influenza infection on mental illness. If relations are found, the implications for primary prevention will be valuable.
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