There is no known single cause of schizophrenia. Many diseases, such as heart disease, result from an interplay of genetic, behavioral, and other factors; and this may be the case for schizophrenia as well. Scientists do not yet understand all of the factors necessary to produce schizophrenia, but all the tools of modern biomedical research are being used to search for genes, critical moments in brain development, and other factors that may lead to the illness.

Modern techniques have demonstrated that some affected people have changes in the structure of their brains. There is also evidence that some of these individuals may have been affected by infections before they were born.

Is Schizophrenia Inherited?

It has long been known that schizophrenia runs in families. People who have a close relative with schizophrenia are much more likely to develop the disorder than are people who have no relatives with the illness. For example, a monozygotic (identical) twin of a person with schizophrenia has the highest risk at 40 to 50 percent of developing the illness. The fact that identical twins do not always share schizophrenia is suggestive of environmental factors. A child whose parent has schizophrenia has about a 10 percent chance. By comparison, the risk of schizophrenia in the general population is about 1 percent.

Scientists are studying genetic factors in schizophrenia. Multiple genes have been linked to a predisposition to developing the disorder. In addition, factors such as prenatal difficulties like intrauterine starvation or viral infections, perinatal complications, and various non-specific stressors, seem to influence the development of schizophrenia. However, it is poorly understood exactly how these genes contribute to the development of the disorded, and it cannot yet be accurately predicted whether a given person will or will not develop the disorder.

Several regions of the human genome are being investigated to identify genes that may confer susceptibility for schizophrenia. Around 10 genes have been implicated, many of which are generally important in bran development. Identification of the specific genes involved and their contribution to the development of schizophrenia will provide important clues into what goes wrong in the brain to produce and sustain the illness and will guide the development of new and better treatments.

Is Schizophrenia associated with Chemical Defect in the Brain?

Basic knowledge about brain chemistry and its link to schizophrenia is expanding rapidly. Neurotransmitters, substances that allow communication between nerve cells, have long been thought to be involved in the development of schizophrenia. It is likely, although not yet certain, that the disorder is associated with some imbalance of the complex, interacting chemical systems of the brain, probably involving the neurotransmitters dopamine and glutamate, amongst others. Much evidence suggests that dopamine and serotonin are intricately involved in the manifestation of the illness. The individual’s ‘breakdown’ may occur as a result of drug or alcohol misuse, emotional stress or difficulties in life experiences. There is no scientific evidence to support the idea that parenting style can cause schizophrenia in their offspring, and the idea remains extremely controversial.

Is Schizophrenia associated with Physical Abnormality in the Brain?

There have been dramatic advances in neuroimaging technology that permit scientists to study brain structure and function in living individuals. Many studies of people with schizophrenia have found abnormalities in brain structure (for example, enlargement of the fluid-filled cavities, called the ventricles, in the interior of the brain, and decreased size of certain brain regions) or function (for example, decreased metabolic and neurotransmitter activity in certain brain regions). It should be emphasized that these abnormalities are quite subtle and are not characteristic of all people with schizophrenia, nor do they occur only in individuals with this illness. Microscopic studies of brain tissue after death have also shown small changes in distribution or number of brain cells in people with schizophrenia. It appears that many (but probably not all) of these changes are present before an individual becomes ill, and schizophrenia most of what we know about schizophrenia centres on neurodevelopmental abnormalities.

Stress, arising from sudden events like a car accident, bereavement or moving home, often occurs shortly before an episode of schizophrenia, and, though it is not the cause, it almost certainly acts as a ‘trigger’. Long-term stress, such as family tensions, may also make it worse.

At one time, it was fashionable to believe that schizophrenia was created by particularly disturbed families, but there is no evidence to support this idea. Families do not cause schizophrenia. However it does tend to run in families. A child who has an affected parent has a 1 in 10 chance of developing schizophrenia. Viral infections during pregnancy, birth complications, growing up in inner cities and drug misuse also seem to play a part in the development of schizophrenia. The structure and chemistry of the brain may be affected, but there are no simple diagnostic tests for this at present.

Evidence from research suggests that an event such as stressful time or difficult relationship in the family can sometimes trigger an episode of schizophrenia in someone who is already likely to develop it because of genetic and other factors. Anyone can get the symptoms of schizophrenia. People with it may read special meanings into things they see around them. They may feel that everything is wonderful and important, or frightening and strange.

We don’t know exactly what causes these feelings. It is a highly complex disorder resulting from the interactions between multiple environmental and genetic factors. The pervasive nature of the symptoms means that schizophrenia affects the whole person, and possibly the rest of their life, from the outset.

Substance abuse is a common concern of the family and friends of people with schizophrenia. Since some people who abuse drugs may show symptoms similar to those of schizophrenia, people with schizophrenia may be mistaken for people high on drugs. Sometimes families feel that street drugs can bring on schizophrenia yet most researchers do not believe that substance abuse causes schizophrenia. People who have schizophrenia often abuse alcohol and/or drugs, and may have particularly bad reactions to certain drugs. Substance abuse can reduce the effectiveness of treatment for schizophrenia. Stimulants (such as amphetamines or cocaine) may cause major problems for patients with schizophrenia, as may PCP or marijuana. In fact, some people experience a worsening of their schizophrenic symptoms when they are taking such drugs. Substance abuse also reduces the likelihood that patients will follow the treatment plans recommended by their doctors.

Cannabis

An association between cannabis use and schizophrenia was established decades ago (Andreasson, Allebeck et al. 1987) . These findings have been corroborated by further research. Essentially, the conclusions drawn from many of these studies were that cannabis use causes schizophrenia. However, it is unlikely to be so simple. Undoubtedly, these studies are extremely important, although they are far from conclusive.

There may be a number of reasons that could account for the association between schizophrenia and cannabis. For example, it is possible that cannabis use may cause schizophrenia in vulnerable individuals (ie. a risk factor – as smoking cigarettes are to heart disease). On the other hand, it may be that people with schizophrenia are inherently more likely to abuse cannabis, either in an attempt to self medicate or because there is a more general link with substance abuse. Indeed, people with schizophrenia are much more likely to abuse any drug and it is thought that around 50% of people with schizophrenia are substance abusers. Also, mental illness in general is associated with greater rates of substance abuse.

Another interesting study found that mental illness at age 15 was associated with cannabis use at age 18. Conversely, cannabis use at age 18 was associated with mental illness at 21 years. This suggests that in adolescence mental illness causes substance use, but that in adulthood, this may be reversed.

Interestingly, even though rates of cannabis use have significantly increased in recent decades, rates of schizophrenia do not appear to have changed appreciably over this same period.

Does Smoking affect Schizophrenia?

The most common form of substance use disorder in people with schizophrenia is nicotine dependence due to smoking. The prevalence of smokers among those with schizophrenia may be three times higher than the general population. Research has shown that the relationship between smoking and schizophrenia is complex. Although people with schizophrenia may smoke to self medicate their symptoms, smoking has been found to interfere with the response to antipsychotic drugs. Several studies have found that schizophrenia patients who smoke need higher doses of antipsychotic medication. Quitting smoking may be especially difficult for people with schizophrenia, because the symptoms of nicotine withdrawal may cause a temporary worsening of schizophrenia symptoms. However, smoking cessation strategies that include nicotine replacement methods may be effective. Doctors should carefully monitor medication dosage and response when patients with schizophrenia either start or stop smoking.