Biological Explanations for Schizophrenia

• Family studies find individuals who have schizophrenia and determine whether their biological relatives are similarly affected more often than non-biological relatives. There are two types of twins – identical (monozygotic) and fraternal (dizygotic). To form identical twins, one fertilised egg (ovum) splits and develops two babies with exactly the same genetic information.
• Gottesman (1991) found that MZ twins have a 48% risk of getting schizophrenia whereas DZ twins have a 17% risk rate. This is evidence that the higher the degree of genetic relativeness, the higher the risk of getting schizophrenia.
• Benzel et al. (2007) three genes: COMT, DRD4, AKT1 – have all been associated with excess dopamine in specific D2 receptors, leading to acute episodes, positive symptoms which include delusions, hallucinations, strange attitudes.
• Research by Miyakawa et al. (2003) studied DNA from human families affected by schizophrenia and found that those with the disease were more likely to have a defective version of a gene, called PPP3CC which is associated with the production of calcineurin which regulates the immune system. Also, research by Sherrington et al. (1988) has found a gene located on chromosome 5 which has been linked in a small number of extended families where they have the disorder.
• Evidence suggests that the closer the biological relationship, the greater the risk of developing schizophrenia. Kendler (1985) has shown that first-degree relatives of those with schizophrenia are 18 times more at risk than the general population. Gottesman (1991) has found that schizophrenia is more common in the biological relatives of a schizophrenic, and that the closer the degree of genetic relatedness, the greater the risk.