Finnish and German studies offer new insights on illness
By Amy Norton MEDICAL TRIBUNE NEWS SERVICE
July 2 - Researchers have uncovered more clues to the complex mix of environmental and genetic factors that lead to schizophrenia. In a report published in the July issue of the American Journal of Psychiatry, researchers from Finland asserted that in some cases schizophrenia may arise from prenatal exposure to the virus that causes polio.
IN THE SAME ISSUE, German researchers report on evidence that schizophrenia has some characteristics of autoimmune diseases. In these conditions, which include rheumatoid arthritis and multiple sclerosis, the immune system mistakenly attacks the body’s own normal cells. Schizophrenia is a mental illness that impairs thinking, perception and emotion. People with the disorder experience hallucinations, delusions, mood swings and a generally altered view of reality.
Although schizophrenia does not usually become apparent until the late teen years or the 20s, most researchers suspect that the disorder is rooted in early brain development. It is well-established that a family history of schizophrenia increases a person’s risk for developing the condition but environmental factors also appear to play a role. Whether prenatal exposure to the poliovirus is one of these factors was the subject of the Finnish study, led by Dr. Jaana Suvisaari of the National Public Health Institute in Helsinki.
Some experts have long suspected such a connection because cases of schizophrenia declined in many countries after the polio vaccine was introduced. Suvisaari’s team sought to find out whether Finnish women who were pregnant while infected with poliovirus in the 1950s and 1960s were more likely to have children who later developed schizophrenia.
They discovered that among more than 13,500 people born in this period, schizophrenia was more common among those exposed to poliovirus five months before birth versus those not exposed to the virus. A weaker association was found between schizophrenia and exposure to poliovirus at any point in the second trimester of pregnancy. “It’s more support for the hypothesis that prenatal exposure to a viral infection is associated with schizophrenia,” said Dr. Alan Brown, an associate professor of psychiatry at Columbia University in New York. The second trimester, he noted, is an important time in fetal brain development.
GERMAN STUDY Still, Brown said he believes the key to uncovering schizophrenia’s roots lies not in epidemiological studies like the Finnish one, but in identifying specific biological markers of the illness. This was the approach taken in the German study. Researchers led by Dr. Markus J. Schwarz of Ludwig-Maximilian University in Munich found that compared with healthy controls, schizophrenics were far more likely to have antibodies to certain heat shock proteins (HSP) that help protect the cells of the central nervous system.
Among 30 patients with schizophrenia, 33 percent had antibodies to two types of HSP, compared with just 3 percent of healthy controls. HSP antibodies, Schwarz’s team noted, have been found in patients with multiple sclerosis. Experts believe this disease of the central nervous system results from immune- system damage to the covering of nerve cells. This suggests that an immune-system attack on these normal proteins may be involved in schizophrenia. Brown, who was part of the research team that in 1991 first described the increased levels of HSP antibodies in schizophrenics, suggested that antibodies released to fight an infection might also “cross-react” with structures in the central nervous system.
The German study, he noted, is the first to reproduce his team’s findings. Prenatal exposure to poliovirus and the higher presence of HSP antibodies in schizophrenics are just two possible factors in the development of the brain disorder. Brown noted that poor prenatal nutrition and pregnancy complications have also been implicated. In addition, Brown and colleagues have found that prenatal exposure to rubella, as well as diabetes in the mother, seem to increase risk of later being diagnosed with schizophrenia.
“I feel that we’ll find [schizophrenia] is determined by genetic predisposition
coupled with various environmental factors,” Brown said. “Some environmental
factors will be very strong. Others will be so weak that you’ll need to
have several of them to increase the risk.”