When we think of a child’s “environment,” we tend to think of their family and friends. In fact, our first “environment” is inside the womb. The nine months during which a baby develops inside the mother lay important groundwork for healthy development after birth. Researchers have found that there are qualities of the prenatal environment that may increase the likelihood that someone will develop schizophrenia. For example, research has shown that patients with schizophrenia are much more likely to be born following a complicated pregnancy or delivery. Additionally, schizophrenia patients are more likely to be born during winter months. There are two ways in which the prenatal environment may affect an infant with a genetic propensity for schizophrenia.
In 1957, there was an influenza epidemic in Helsinki, Finland. Sarnoff Mednick at the University of Southern California wanted to know if mothers who had the flu while they were pregnant were more likely to have children who later developed schizophrenia. Indeed, Mednick found that children who were born to mothers who had the flu in the second trimester were more likely to have schizophrenia as adults. Although researchers are still uncertain as to how exactly the influenza virus affects the unborn child, one hypothesis is that maternal antibodies cross the placental barrier and disrupt brain development.
Children whose mothers are malnourished may also be more likely to develop schizophrenia as adults. The Dutch Hunger Winter was a period of extreme famine in the Netherlands. In 1944, a Nazi blockade prevented many Dutch citizens from getting enough food for their families. Many people became very sick and some died from starvation. Research has shown that the children who were conceived at the height of the famine were twice as likely to develop schizophrenia as children who were conceived at other times. Fetal malnutrition may play a role in the development of schizophrenia.
What Causes Schizophrenia?
Schizophrenia is a complex illness, and no single cause has been found. There are several theories about the causes, which include:
- Heredity. Schizophrenia runs in some families. A person can inherit a tendency to develop the illness, especially if a parent has the disorder. The risk for inheriting schizophrenia is 10 percent in those who have an immediate family member with the illness, and 40 percent if the illness affect both parents or an identical twin. However, about 60 percent of people with schizophrenia have no close relatives with the illness
- Brain chemistry. Many researchers believe that people with schizophrenia are either very sensitive to a brain chemical called dopamine, or produce too much of it. Dopamine is a neurotransmitter, which are substances that allow nerve cells in the brain to send messages to each other. An imbalance of this chemical can affect the way a person’s brain reacts to stimuli.
- An abnormality within the brain. Better imaging technology has allowed researchers to study the brain structure and function in people with schizophrenia. They have concluded that many individuals with the disorder have subtle abnormalities in brain structure. These abnormalities include a slight enlargement of the fluid-filled cavities (ventricles) in the brain, and a slightly smaller size of some areas of the brain. But this is not true in all people with schizophrenia, and such abnormalities also have been identified in people who do not have schizophrenia.
- Complications during pregnancy and birth. Some researchers believe that an infection or malnutrition during pregnancy, or by complications during birth, may increase the chances of that child developing schizophrenia when he or she is older.
Can schizophrenia be inherited?
Scientists have long known that schizophrenia runs in families. It occurs in 1 percent of the general population but is seen in 10 percent of people with a first-degree relative (a parent, brother, or sister) with the disorder. People who have second-degree relatives (aunts, uncles, grandparents, or cousins) with the disease also develop schizophrenia more often than the general population. The identical twin of a person with schizophrenia is most at risk, with a 40 to 65 percent chance of developing the disorder.7
Our genes are located on 23 pairs of chromosomes that are found in each cell. We inherit two copies of each gene, one from each parent. Several of these genes are thought to be associated with an increased risk of schizophrenia, but scientists believe that each gene has a very small effect and is not responsible for causing the disease by itself. It is still not possible to predict who will develop the disease by looking at genetic material.
Although there is a genetic risk for schizophrenia, it is not likely that genes alone are sufficient to cause the disorder. Interactions between genes and the environment are thought to be necessary for schizophrenia to develop. Many environmental factors have been suggested as risk factors, such as exposure to viruses or malnutrition in the womb, problems during birth, and psychosocial factors, like stressful environmental conditions.
Heather Barnett Veague, Ph.D.
Heather Barnett Veague attended the University of California, Los Angeles, and received her Ph.D. in psychology from Harvard University in 2004. She is the author of several journal articles investigating information processing and the self in borderline personality disorder. Currently, she is the Director of Clinical Research for the Laboratory of Adolescent Sciences at Vassar College. Dr. Veague lives in Stockbridge, Massachusetts, with her husband and children.