Family studies have established that schizophrenia is more common among genetic relatives of a person with schizophrenia, and that the closer the degreee of genetic relatedness, the greater the risk. For example, Varma et al (1997) looked at the first-degreee relatives (FDRs) of about 1,000 schizophrenics and 1,000 controls. Psychiatric illness was found in 16% of the /fdrs of schizophrenics compared with 7% of the controls.
Twin studies If monozygotic (MZ) twins (who share 100% of their genes) are more concordant (similar) than are dizygotic (DZ) twins (who on average share only 50% of their genes), then this suggests that the greater similarity is due to genetic factors. Joseph (2004) calculated that the pooled data for all schizophrenia twin studies carried out prior to 2001 shows a concordance rate for MZ twins of 40.4% and 7.4% for DZ twins.
Adoption studies Studies of genetic relatives fail to disentangle the effects of shared genes and shared environment since relatives (e.g. siblings) live together. One laternative is to compare adopted children with and without biological parents diagnosed with schizophrenia. For example, Tienari et al (2000) studied 164 adoptees whose biological mothers had been diagnosed with schizophrenia, and found that 11 (6.7%) also received a diagnosis of schizophrenia, compared with just 4 (2%) of the 197 control adoptees (born to non-schizophrenic mothers).
The dopamine hypothesis
The dopamine hypothesis states that messages from neurons that transmit dopamine fire too easily ot too often, leading to the characteristic symptoms of schizophrenia. Schizophrenics are thought to have abnormally high numbers of D2 receptors on receiving neurons, resulting in more dopamine binding and therefore more neurons firing. Dopamine neurons play a key role in guiding attention, so distrubances in this process may weel lead to the problems of attention, perception and thought found in people with schizophrenia (Corner, 2003).
Brain ventricles are the cavities in the brain that contain nutrients. On average, the ventricles of a person with schizophrenia are about 15% bigger than normal (Torrey, 2002). It may be that the enlarged ventricles are the result of poor brain development or tissue damage.
Freud (1924) believed that schizophrenia was the result of two processes, (1) regression to pre-ego stage; and (2) attempts to re-establish ego control. Harsh experiences, such as having uncaring parents, leads to regression as an ego defence. Schizophrenia was thus seen by Freud as an infantile state, with some symptoms (e.g. delusions of grandeur) reflecting this primitive condition and other symptoms (e.g. auditory hallucinations) reflecting the person's attempts to re-establish ego control.
Biological factors cause the initial sensory experiences of schizophrenia, but further features of the disorder appear as individuals attempt ti understand those experiences. When schizophrenics first experience voices and other worrying sensory experiences, they turn to others to confirm the validity of what they are experiencing. Other people fail to confrim the relaity of these experiences, so the schizophrenic comes to believe that the others must be…