Maternal influenza link to bipolar disorder refined

Research suggests that maternal influenza during pregnancy may increase the risk for bipolar disorder with psychotic features in offspring, rather than being associated with bipolar disorder per se.

“These results provide further evidence that parsing bipolar disorder case subjects into those with and those without psychotic symptoms may be another meaningful way to reduce the heterogeneity of this disorder in order to provide insight into particular neurobiological systems that may be disturbed,” say the researchers.

In their case–control study, maternal influenza exposure during pregnancy – overall or during specific trimesters – was not associated with bipolar disorder in offspring, at a nonsignificant odds ratio of 1.26.

However, study participants whose mothers were exposed had a significant 5.03-fold increased risk of bipolar disorder with psychotic features compared with participants whose mothers were not exposed, whereas there was no increase in the risk of nonpsychotic bipolar disorder.

There were a total of 85 patients with bipolar disorder (predominantly type I) in the study, identified from the Child Health and Development Study birth cohort, and 170 controls matched for variables including age and gender. In total, 63 mothers of these study participants had serological evidence of influenza exposure in samples taken during pregnancy.

The association between maternal influenza and psychotic bipolar disorder persisted after accounting for maternal race and psychiatric history, at a 4.87-fold increased risk, report Alan Brown (Columbia University College of Physicians and Surgeons, New York, USA) and co-workers in The American Journal of Psychiatry.

“Since prenatal influenza has been previously associated with schizophrenia, a disorder characterized in large part by psychotic episodes such as hallucinations and delusions, our results support the hypothesis that maternal influenza exposure may preferentially increase the risk for psychosis apart from traditional diagnostic categories,” they write.

The risk of psychotic bipolar disorder associated with maternal exposure during specific trimesters was nonsignificant, but was elevated for exposure during the first and second trimesters, at respective odds ratios of 3.4 and 4.0, but not the third trimester, at an odds ratio of 1.0.

“Although replication in independent samples is essential, these findings imply that prevention of influenza exposure during pregnancy may decrease the incidence of bipolar disorder with psychotic features in the population,” say Brown et al.

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