How is Schizophrenia Caused?

by Rethink

(Page 3 of 4)

Most scientists believe that psychiatric disorders are usually the produces of multiple interacting causal factors. Studies of significant causes and processes in the development of mental illness have found physical, mental, enviornmental and emotional causes for mental illness.

genetic causes

Because schizophrenia tends to run in families, researchers have been searching for specific genes, passed down through generations that may increase a person's chance of developing the illness. The evidence that heredity plays a role in the development of some forms of mental illness has been discovered by studying identical twins who were raised seperately and studying adopted children of mothers with different forms of severe mental illness and comparing them to non-identical twins raised separately and the general public.

If an identical twin raised seperately from its twin develops schizophrenia, then the chance that the other twin will also develop it is 50% or 1 chance in 2. In non-identical twins however, who would share on average only half of their genetic makeup, where one twin develops schizophrenia, there is only a 15% or 15 chances in 100 that the other twin will also develop the disorder. While this is higher than for the general population who have about 1 chance in 100 of developing the condition, it suggests that heredity is not the only factor influencing the developent of schizophrenia in these families.

However, what exactly is inherited? The neurotransmitter system - the chemical messenger system of the body - has recieved a great deal of attention as a possible cause of schizophrenia. Researchers have known for decades that there is a link between neurotransmitters and schizophrenia, because drugs which alter these transmitters also relieve schizophrenia. Some studies hypothesize that a low or high level of a specific neurotransmitter such as dopamine and serotonin is the cause. Others indicate that an imbalance of these substances is the problem. Still other studies have found that the a change in the sensitivity of the receptors on nerve cells that receive the neurotransmitter messages is at least part of the cause of schizophrenia.

There is some evidence that genetic factors may influence the membrane structures and metabolism of nerve cells. The structure of the membranes around neurones is dependent upon levels of certain essential fatty acids in the blood. People with schizophrenia have been found to have lower levels of these fatty acids.

abnormal brain development

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 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 may be, in part, a disorder in development of the brain.

Developmental neurobiologists have found that schizophrenia may be a developmental disorder resulting when neurons form inappropriate connections during foetal development. These errors may lie dormant until puberty, when changes in the brain that occur normally during this critical stage of maturation interact adversely with the faulty connections. This research has spurred efforts to identify prenatal factors that may have some bearing on the apparent developmental abnormality.

infection

In recent years, there has been an accumulation of experimental and epidemiological evidence supporting the role of viral infections in the development of schizophrenia. Among those implicated is the poliovirus, the flu virus and a virus called encephalitis lethargica.

birth complications

Complications during pregnancy, abnormal foetal growth and complications during delivery are significant risk factors in the development of schizophrenia. Those that play a significant role in the development of schizophrenia include:

• complications of pregnancy including bleeding, diabetes and pre-eclampsia
• abnormal foetal growth and development including conditions such as low birthweight and reduced head circumference
• complications of delivery including asphyxia (lack of oxygen) and emergency Caesarean section.

However, the effect of such complications is small in comparison with factors such as genetic pre-disposition to schizophrenia.

head injury

Traumatic head injury, such as that sustained in a fall or traffic accident can cause symptoms of psychosis. How head injury plays a role in the development of schizophrenia is unknown. Researchers state that childhood head injury could interact with genetic predisposition leading to the development of schizophrenia.

psychological causes

The main psychological trigger that can lead to the onset of symptoms of schizophrenia is stressful life events. These can range from a death in the family to the loss of a job, from the birth of a child to a move. Stresses and strains may be different for one person to another.

Recent research has suggested that social factors play a key role in the development of schizophrenia amongst the UK's African Caribbean population. The study found that when African-Caribbeans in Trinidad, Barbados and London were compared there was a lower rate of schizophrenia in Trinidad and Barbados than amongst African-Caribbeans living in the UK. This suggests that there is no genertic vulnerability to schizophrenia in African Caribbeans. The study also found that rates of schizophrenia are higher amongst second genreation African-Caribbeans than in those originally migrated to the UK. This suggests that social factors play a part in the develoment of schizophrenia. It has been suggested that possible causing factors include stress caused by institutional and individual racism, low employment levels, poor housing and lack of cultural identity. Research has also shown that the smaller the proportion of an ethnic minority living in an area the greater the risk of developing a mental illness becomes. Social isolation is thought to pay an imporatnat role in such stresses.

drug use

It is a common incorrect belief that drug use causes schizophrenia. Drugs do not directly cause schizophrenia, however, certain drugs (such as cannabis, LSD or amphetamines) may cause a disturbance in the brain that can trigger a first episode.

About the Author

www.rethink.org
Rethink is the largest severe mental illness charity in the UK. We are dedicated to improving the lives of everyone affected by severe mental illness, whether they have a condition themselves, care for others who do, or are professionals or volunteers working in the mental health field.