Schizophrenia Not Linked to Prenatal Exposure to Influenza
"I think this is an excellent paper. The investigators use the Danish
Registry Data which has been developed over decades which is just now bearing
fruit for schizophrenia research", Ezra Susser, MD, DrPH, tells WebMD.
"They looked at things rarely examined in schizophrenia research: birth
order, sibship size, space between siblings. As far as the small interval
between siblings, you can't make too much of the findings yet but they're
"They tested the influenza hypothesis in a much better way than previous
studies," he says. Susser, the head of the Epidemiology of Brain Disorders
program at the New York State Psychiatric Institute and Columbia University,
was not associated with the Westergaard research.
Other experts aren't so sure. "This study casts further doubt that
influenza is an important infection in causing later cases of schizophrenia.
However, I take serious exception to the conclusion that in utero infections
are not important," E. Fuller Torrey, MD, tells WebMD. "Increasingly
research, including our own, has shown that infections both in utero or in
early childhood may well play a role in later development of both schizophrenia
and bipolar disorder." Torrey, who also is not associated with the study,
is from the developmental neurovirology laboratory of the Stanley Research
Foundation for Research in Schizophrenia and Bipolar Disorder in Bethesda,
"It's important to stress that there is no database in the world as good
as the database they are using, which consists of the entire population of
Denmark, to answer the kinds of questions they're asking", says Torrey.
"However, the big problem with these influenza studies is that it doesn't
tell you whether the mother [of the schizophrenia patient] actually had it or
not. You're not going to be able to measure what's going on in utero by
measuring the incidence of maternal symptoms or infections in the
community." He suggests there may be women who have influenza but do not
report it to the medical authorities or perhaps are asymptomatic or only mildly
Torrey adds, "Pregnancy is like a black box. It's conceivable that
there's a whole series of things going on, including infections, and we only
have the vaguest idea of what's going on. We can only measure the most extreme
ends of the spectrum."
- It is unknown what causes schizophrenia, but scientific theories suggest
there is a genetic component, possibly combined with an exposure to infections
either in the womb or during early childhood.
- A new study finds that having a lot of siblings, especially ones that are
closely spaced, is associated with a higher risk of schizophrenia.
- This finding adds evidence to the hypothesis than an infection during early
childhood is somehow related to schizophrenia, since a family with many, close
siblings will likely have more exposure to infections.