Causes of schizophrenia

Most scientists believe that psychiatric disorders are usually the result of multiple interacting causal (trigger) factors. Studies of significant causes and processes in the development of mental illness have found physical, psychological and environmental or social causes for mental illness.

Physical causes

Genetics
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 and comparing them to non-identical twins raised separately and the general public.

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

However, what exactly is inherited? The neurotransmitter system - the chemical messenger system of the body - has received a great deal of attention as a possible cause of schizophrenia. Drugs which alter these transmitters relieve schizophrenia, which certainly indicates that they are part of the cause. Studies hypothesize that a low or high level of a specific neurotransmitter such as dopamine or serotonin is the cause, that an imbalance of these substances is the problem, or that the change in the sensitivity of the receptors on nerve cells that receive the neurotransmitter messages may be factors in the cause of schizophrenia.

Genetic factors may also influence the membrane structures and metabolism of nerve cells. The structure of the membranes around neurones is dependent upon the right 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 or in the way it functions. 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.

Studies of brain tissue have also shown small changes in number of brain cells or how they are distributed 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.

Schizophrenia may also be a developmental disorder resulting when neurons in the brain form the wrong connections during foetal development. These errors may be unnoticed until puberty, when changes in the brain that occur normally during this time of important changes are effected by the faulty connections. There is now much research being carried out in this area.

Infection
 In recent years, there has been a build up of evidence supporting the role of viral infections in the development of schizophrenia, including 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:

  • bleeding, diabetes and pre-eclampsia pregnancy complications 
  • abnormal foetal growth and development problems including conditions such as low birth weight 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 from 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 such an injury to the head could interact with genetic make-up, leading to the development of schizophrenia.

It is a commonly held 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, especially in those that may already be pre-disposed to mental health problems like those who have history of mental illness in the family.

Psychological causes

The main psychological trigger that can lead to the onset of symptoms of schizophrenia is ‘stressful life events’. These could be anything such as a death in the family, the loss of a job or even the birth of a baby.

Recent research has suggested that social factors play a key role in the development of schizophrenia amongst the UK's African Caribbean population, even when they have no genetic vulnerability to the illness. This suggests that social factors play a part in the development of schizophrenia, such as 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 important role in such stresses.