Ra. Machon et al., ADULT MAJOR AFFECTIVE-DISORDER AFTER PRENATAL EXPOSURE TO AN INFLUENZA EPIDEMIC, Archives of general psychiatry, 54(4), 1997, pp. 322-328
Background: We have previously reported an increase in schizophrenia d
iagnoses in a population exposed during the second trimester to the 19
57 influenza epidemic. These basic findings together with a fair numbe
r of replications have been interpreted as supporting a neurodevelopme
ntal contribution to the origins of schizophrenia. Recent neuroimaging
findings suggest that affective illness may also have a neurodevelopm
ental origin. We examined the hypothesis that exposure to an influenza
epidemic during the second trimester would increase the risk for adul
t major affective disorder. Methods: The subjects had been exposed as
fetuses to the type A(2)/Singapore influenza epidemic in greater Helsi
nki, Finland. Control subjects were born in the 6 years before the epi
demic. Results: We found a significant (P<.001) increase in the propor
tion of hospital diagnoses for major affective disorder for individual
s exposed to the influenza epidemic during their second trimester of f
etal development compared with control subjects (13% vs 2%). This seco
nd-trimester effect seems somewhat stronger in men (16% vs 2%) (P<.001
), although the rates of major affective disorder in women (8% vs 3%)
(P>.05) were similar. The second-trimester effect remained when we est
imated population-based rates (2.1 vs 0.6 per 1000) (P<.05) of major a
ffective disorder. Additional analyses revealed that the increase of m
ajor affective disorder among subjects in the index group who were exp
osed during the second trimester was due: to a significant (P<.002) el
evation of unipolar forms, although a similar though not significant (
P>.05) elevation was observed for the bipolar forms of major affective
disorder. Conclusions: These data are consistent with the hypothesis
concerning the possible neurodevelopmental contribution to the origins
of some forms of major affective disorder, especially unipolar depres
sive disorder. These encouraging findings, if replicated may suggest t
hat some mental disorders may stem, in part, from a disturbance in the
development of the fetal brain during the second trimester.