A Theory That Raises Questions
Tuesday, November 27, 2007
Over the past several decades, a steady stream of studies has documented that people born in winter and spring have an increased risk for schizophrenia, a serious mental illness characterized by disordered thinking, hallucinations and other psychotic symptoms.
Explanations for the increased risk have ranged from the astrological -- different signs of the zodiac have been associated with various mental problems -- to accounts that suggested the risk came from seasonal variations in sunlight.
In recent months and years, scientists have developed a different explanation: Studies show the increased risk of schizophrenia appears linked to maternal infections during the first and second trimesters of pregnancy -- especially flu infections. Since the flu peaks in the fall, this might explain why babies born in the winter and spring have the higher risk.
The research is both intriguing and troubling. For one thing, it suggests that the origins of diseases such as schizophrenia might start as early as the womb. Indeed, symptoms of schizophrenia, which typically emerge in late adolescence or early adulthood and affects about 1 percent of the population, may only be the very last stage in a long process.
"Often what we see in the form of schizophrenia, bipolar disorder and even some of the more neurological disorders like Alzheimer's disease [is] the end stage where people show symptoms," said Thomas Insel, director of the National Institute of Mental Health. "The best model is in Parkinson's disease: You don't show the symptoms until you have lost 80 percent of the neurons in the substantia nigra," an area of the brain that helps produce the neurotransmitter dopamine.
But if research into the links between early maternal infections and schizophrenia might one day provide researchers with clues about how to attack the disease before symptoms become apparent, it also raises difficult public health conundrums.
That's because the newest studies suggest the culprit may not be infections such as the flu per se, but pregnant mothers' immune reactions to such infections. Current guidelines recommend that pregnant women get a flu shot -- and the point of the flu vaccine is to set off an immune reaction. If the risk for schizophrenia is increased as a result of maternal antibodies, might protecting mom and baby from the flu raise the risk the child could get schizophrenia years down the road?
The research into the links between maternal flu and schizophrenia is still considered preliminary, which makes any policy conclusions premature, but scientists studying the connection are starting to worry. National guidelines issued by the Centers for Disease Control and Prevention recommend that pregnant women get flu shots.
"Obviously, the safe thing to do is to go with the experts, and the experts are the CDC," said Paul Patterson, a professor of biology at the California Institute of Technology and one of the leading researchers into the link between maternal infections and schizophrenia. "However, if it was my wife, I would not [want] her vaccinated."
Patterson said he would try to protect a pregnant family member from the flu by suggesting she keep away from infected people and by enforcing a regimen of regular hand-washing among all family members.
However, he conceded that such measures might not be as effective as flu shots and that women who get the flu because they don't get a flu shot might not only put their future children at increased risk for schizophrenia, but also incur numerous other risks from the illness. Careful prevention techniques, moreover, are unlikely to help pregnant women who have toddlers, because small children tend to bring home endless streams of viral infections.
Insel praised Patterson's research into the connection between infections and schizophrenia, but he warned against rushing to revise flu shot recommendations.