Adult schizotypal personality characteristics and prenatal influenza in a Finnish birth cohort.

Recent evidence suggests that schizophrenia may result from a disruption of normal brain development during a critical, prenatal risk period in the 6th month of gestation. The phenotypic diagnostic manifestation of a basic genetic-neurodevelopmental disorder may consist of characteristics approximated by the DSM-IV diagnosis of "schizotypal personality disorder" (SPD). We identified male conscripts in Finland who, as fetuses, were exposed to the 1969 Hong Kong Influenza epidemic, along with a group of controls born during a relatively low year (1971) for infectious epidemics. It was hypothesized that among fetuses exposed to the influenza epidemic in their 6th month of gestation, we would observe an increased frequency of elevated (upper quartile) scores on a schizotypal personality characteristics (SPC) scale as compared to controls. A significantly higher proportion of the 6th month index exposed subjects (39%) had "elevated" SPC scale scores as compared to their controls (26%) (p<0.003). Further analyses revealed that these differences were accounted for by those exposed to the influenza epidemic in week 23 (51% vs. 24%) of the 6th month (p<0.005). Exploratory analyses for the other months did not reveal any significant differences. Implications and limitations of the week 23 findings are discussed.